Abstract:
A low height disk drive having an overall height of approximately one inch (1″). The drive includes a head disk assembly, including a base plate, two disks rotatably supported on the base plate, a motor for rotating the disks, at least two heads for reading information from and writing information on respective ones of the disks; an actuator, supported on the base plate and responsive to control signals, for selectively positioning the heads with respect to the disks, and a cover sealably attached to the base plate to enclose the storage device, the head, and the actuator. The disk drive also includes control circuitry for generating control signals, and for providing information signals to and receiving information signals from the heads. The head disk assembly and the control circuitry have a combined height of approximately one inch or less.

Description:
DIVISIONAL APPLICATION INFORMATION 
     This Application is a divisional application of Ser. No. 09/285,936, filed Apr. 2, 1999, entitled LATCH MECHANISM FOR DISK DRIVE USING MAGNETIC FIELD OF ACTUATOR MAGNETS, now U.S. Pat. No. 6,429,999, which is a continuation of application of Ser. No. 08/622,925, filed Mar. 27, 1996, now U.S. Pat. No. 5,956 213, which is a continuation application of Ser. No. 08/400,463, filed Mar. 7, 1995 now abandoned, which is a continuation application of Ser. No. 08/110,539, filed Aug. 23, 1993 now abandoned, which is a divisional application of Ser. No. 07/796,576, filed Nov. 22, 1991 now abandoned, which is a continuation-in-part of application Ser. No. 07/549,283 filed Jul. 6, 1990, which is a continuation-in-part of application Ser. No. 07/147,804, filed Jan. 25, 1988, now U.S. Pat. No. 4,965,684. 
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     1) LOW HEIGHT DISK DRIVE, inventor Frederick M. Stefansky, Ser. No. 147,804, Filed Jan. 25, 1988, now U.S. Pat. No. 4,965,684; 
     2) DISK DRIVE SYSTEM CONTROLLER ARCHITECTURE, inventors John P. Squires, Tom A. Fiers, and Louis J. Shrinkle, Ser. No. 057,289, filed Jun. 2, 1987, now U.S. Pat. No. 4,979,056; 
     3) DISK DRIVE SOFTWARE SYSTEM ARCHITECTURE, inventors John P. Squires, Tom A. Fiers; and Louis J. Shrinkle, Ser. No. 488,386, filed Feb. 23, 1990, now U.S. Pat. No. 6,279,108, which is a continuation of Ser. No. 057,806, filed Jun. 2, 1987, now abandoned; 
     4) DISK DRIVE SYSTEM CONTROL ARCHITECTURE UTILIZING EMBEDDED REAL-TIME DIAGNOSTIC MONITOR, inventor John P. Squires, Ser. No. 423,719, filed Oct. 18, 1989, now U.S. Pat. No. 4,979,055, which is a continuation of Ser. No. 058,289, filed Jun. 2, 1987, now abandoned; 
     5) LOW-POWER HARD DISK DRIVE ARCHITECTURE, inventors John P. Squires and Louis J. Shrinkle, filed Aug. 7, 1990, Ser. No. 564,693, now U.S. Pat. No. 5,402,200, which is a continuation of Ser. No. 152,069, filed Feb. 4, 1988, now abandoned; 
     6) DISK DRIVE SYSTEM USING MULTIPLE EMBEDDED QUADRATURE SERVO FIELDS, inventors Louis J. Shrinkle and John P. Squires, Ser. No. 386,504, filed Jul. 27, 1989, now U.S. Pat. No. 5,381,281; 
     7) MAGNETIC PARKING DEVICE FOR DISK DRIVE, inventor, Frederick Mark Stenfansky, Ser. No. 643,703, filed Jan. 22, 1991, now U.S. Pat. No. 5,170,300, which is a continuation of Ser. No. 269,873, filed Nov. 10, 1988, now abandoned; 
     8) MULTIPLE MICRO CONTROLLER HARD DISK DRIVE CONTROL ARCHITECTURE, inventors John P. Squires, Charles M. Sander, Stanton M. Keeler, and Donald W. Clay, Ser. No. 07/611,141, filed Nov. 9, 1990, now U.S. Pat. No. 5,261,058. 
     Each of these related Applications is assigned to the assignee of the subject Application and hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to disk drives; more particularly to hard (or fixed) disk prompted reductions in the size and increases in memory capacity of disk drives. 
     2. Description of the Related Art 
     Developments in personal computers, portable computers and lap top computers have prompted reductions in the size and increases in memory capacity of disk drives. Attempts to provide further reductions in the size and weight, and increases in durability and memory capacity of existing disk drives have been met with limited success. The size (particularly the height) and weight of fixed or hard disk drives and the inability of existing hard disk drives to withstand physical shocks and/or vibrations have been factors which have prevented the incorporation of fixed disks in lap-top and in some cases even larger portable computers. 
     Existing disk drives incorporate a large number of mechanical parts. Each part in a disk drive also represents an increase in the weight of the drive and the space occupied by the drive. A large number of mechanical components makes manufacturing difficult and expensive and increases the possibility and probability of the mechanical failure of the drive. Importantly, the number of mechanical components is related to the ability of the drive to survive physical shocks and vibrations. 
     Resistance to physical shocks and vibrations is critical to protecting the disk or disks, the head or heads, and the various bearings in a disk drive from damage; in particular, it is necessary to prevent damage to the disks which can cause a loss of data, and damage to the heads or the bearings which can end the life of a drive, resulting in a total loss of data. Prior disk drives, however, have limited resistance to physical shocks. Resistance to physical shocks is of paramount importance in portable computers. 
     In conventional drives mechanical distortion or flexing of the mechanical components of a disk drive which support the heads and disks causes tracking problems by moving the heads, which are mounted at one point on the supporting components, relative to the disk, which is mounted at another point on the supporting components. The heads associated with the top and bottom surface of a disk can move relative to the disk to the point where the different heads are in different cylinders—a cylinder being defined as a vertical segment representing the same track on the top and bottom surface of the disk. This problem is known as mechanical off-track and is compounded by increased track densities. 
     Another problem with prior disk drives is the difficulty in sealing the drives to protect the disks from contaminants. This difficulty arises in part, from the large number of points at which access is provided to the environment in which the disk resides. These access points are utilized to bring to the interior of the disk drive electrical circuits which provide current to the motor which rotates the disk, transmit data signals to and from heads which read and record information on the disks, and in some instances, provide current to a voice coil for positioning the head (or heads) which respect to the disk or disks. 
     Many of these disadvantages of prior disk drivers are attributable to the casing—a three-dimensional casting or so-called “toilet bowl”—in which the disks reside. Such a casing is a large, three dimensional piece of cast metal, usually aluminum, having a round portion where the disks reside—hence the name “toilet bowl.” A top plate covers the entire open top of the casing, forming a seal therewith. 
     The spindle on which the disks rotate is supported by and extends through both the casing and the cover. 
     The protrusion of the spindle through the casing and the cover provides points of entry for contaminates. Further, in disk drives using stepper motors to position the heads with respect to the disk, the stepper motor is located outside of the casing, requiring a seal between the stepper motor and the casing. Acknowledging the existence of points where contaminants can enter the disk drive, manufacturers of conventional disk drives provide a breather filter and design the disk drives so that the rotation of the disks causes the disk drivers to exhaust air through leaks in the seals and to intake air only through the breather filter. However, a fairly course filter must be provided in the breather filter for flow of the air to exist, and thus contaminants enter the disk drive through the filter paper. 
     A cast casing is difficult to manufacture with precision, particularly the location of mounting points for elements of the drive supported by the casing. Mounting holes must be drilled after the casting is cast, and the mounting holes must be aligned with the casing and with each other. More importantly, however, a three-dimensional, cast casing flexes due to thermal stresses causing the above-mentioned mechanical off-track problems. 
     In conventional disk drives which use a voice coil to pivot an actuator arm in order to position the heads with respect to the disk, a flex circuit, having one end attached to the actuator arm and the other end attached to a fixed point in the disk drive, transfers the information signals to and from the heads. The standard orientation of such a flex circuit is a loop extending away from the disk. The distance between the point at which the flex circuit is attached to the actuator and the end of the disk drive is limited, and thus the radius of the arc or curve of the flex circuit is small and the length of the flex circuit itself is limited. Therefore, the entire flex circuit moves when the actuator arm is pivoted and a torque is exerted on the actuator arm by the flex circuit. The torque exerted on the actuator arm must be compensated for, either added to or subtracted from the torque created by the voice coil when performing a seek operation. This compensation is complicated by the fact that the torque exerted on the actuator by the flex circuit varies with the position of the actuator. 
     Various types of locking (or latch) devices have been used to lock the arm of a voice coil in a particular position when the disk drive is not operating. The trend in latch devices is to utilize a high power unit which is separately assembled to provide reliability. However, high power latch devices generate a large amount of heat which is not desirable in a disk drive or any other area in a computer. Further, the operation of conventional latch devices can be position dependent. Thus, the orientation of the dick drive and the computer in which the disk drive is installed could affect the reliability of the latch device. Such a positional dependence of reliability is not satisfactory for portable computers. 
     With the ever-increasing storage available on individual magnetic disks, and the ever-increasing speed at which microprocessors such as Intel&#39;s 80386 and 80486 chips operate, the data access time of the disk drive is critical to overall system performance. In many cases, the speed at which the disk accesses data and provides it to the microprocessor is the main performance bottleneck in the system. One critical factor in disk access time is the “seek time” of a drive, generally defined as the time the actuator takes to access particular data at a particular track location on the magnetic disk. The total access time is generally a function of the efficiency of the actuator motor in moving the read/write heads along the arcuate path between consecutive tracks of the disk, and the data throughput of the control electronics. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a disk drive having a low height and a low weight. 
     A further object of the present invention is to provide a multiple platter (disk), disk drive having a one-inch height form factor. 
     Another object of the present invention is to provide a disk drive which is resistant to damage from physical shocks. 
     Another object of the present invention is to provide a low height disk drive having an increased data storage capacity. 
     Another object of the present invention is to provide a disk drive in which any mechanical off tracking of the heads is mechanically minimized and electronically corrected. 
     Another object of the present invention is to provide a disk drive assembly in which a single electrical connector transfers all electrical currents and data signals from the environment in which the disks reside to the exterior of the environment, and in which a header which communicates those electrical signals through the base plate is the only communication between the interior and the exterior of the drive. 
     Another object of the invention is to provide an improved voice coil motor design, and specifically a disk drive having an efficient actuator positioning mechanism. 
     These and other objects of the present invention are provided by a disk drive, including: a head-disk assembly, having a base having a top and a bottom, storage means, supported on said top of said base, for storing data, solid storage means comprising two disks, interactive means for reading information from and writing information on said disks, actuator means, supported on said base and responsive to control signals, for selectively positioning said interactive means with respect to said disks means, and a cover sealably attached to said base to enclose said disks, said interactive means, and said actuator means; and control means, mounted on said head-disk assembly so that said control means is adjacent to said bottom of said base, for generating control signals to control said actuator means and for providing information signals to and receiving information signals from said interactive means, said head-disk assembly, said control means having overall maximum height of approximately one inch (1″). 
     A specific advantage of the present invention is that the disk drive has a reduced height with respect to conventional disk drives utilizing disks of approximately the same diameter. In particular, the three and one-half inch (3.5″) single platter and multiple platter drives of the present invention have an overall height of one inch (1″). Furthermore, the disk drive of the present invention is light in weight—the drives of the present invention weigh slightly more than one pound. 
     A further advantage of the present invention is that a single electrical connector (header) a transfers all electrical signals between the exterior and the interior of the casing reducing the possibility of the introduction of contaminants into the controlled environment within the casing. Importantly, the disk drive of the present invention does not require a breather filter. 
     A further advantage of the disk drive of the present invention is that it includes a voice coil actuator assembly including means for mounting a plurality of read/write heads with respect to a storage means; and means for positioning said mounting means at a plurality of positions with respect to said disk, wherein said means for positioning has relatively equal efficiency between the inside diameter and the outside diameter of the disk. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1-7 illustrate a first embodiment of the disk drive of the present invention. In particular: 
     FIG. 1 is an isometric view of the first embodiment of a disk drive according to the present invention; 
     FIG. 2 is an isometric view of the first embodiment of the disk drive of the present invention with the cover removed; 
     FIG. 3 is a cross-sectional view along line  3 - 3 ′ of FIG. 2; 
     FIG. 4 is an exploded view of the first embodiment of the disk drive of the present invention; 
     FIG. 5 is an end view of the first embodiment of the disk drive of the present invention; 
     FIG. 6 illustrates the actuator assembly; and 
     FIG. 7 illustrates the latch mechanism. 
     FIGS. 8-12 illustrates a second embodiment of the disk drive of the present invention. In particular: 
     FIG. 8 is an isometric view of the second embodiment of a disk drive according to the present invention with the cover removed; 
     FIG. 9 is an expanded isometric view of the second embodiment of the disk drive of the present invention; 
     FIG. 10 is an exploded, isometric, bottom view of the printed circuit board and the base of the second embodiment of a disk drive according to the present invention; 
     FIG. 11 is an end view of the second embodiment of a disk drive according to the present invention; 
     FIG. 12 is an exploded, isometric view of a portion of the actuator and the latch mechanism utilized in the second embodiment of the present invention. 
     FIGS. 13-19 illustrate a third embodiment of the disk drive of the present invention. In particular: 
     FIG. 13 is an exploded, isometric view of the third embodiment of the disk drive according to the present invention; 
     FIG. 14 is a plan view of the third embodiment of the disk drive according to the present invention; 
     FIG. 15 is a view along line  15 — 15  in FIG. 14; 
     FIG. 16 is an exploded, partial view of the actuator assembly of the third embodiment of the disk drive of the present invention; 
     FIG. 17 is a partial plan view of the actuator assembly of the third embodiment of the present invention; 
     FIG. 18 is a cross-sectional view along line  18 — 18  in FIG. 17; 
     FIG. 19 is an enlarged, cross-sectional view of the gasket and cover assembly along line  19 — 19  in FIG.  13 . 
     FIG. 20 is a plan view of the actuator assembly of the third embodiment of the present invention with the top plate and top magnet removed, detailing the relationship between the actuator coil and actuator magnet construction used therein. 
     FIG. 21 is a graph representing the relative magnitude of the torque exerted on an actuator arm by the voice coil motor of the first embodiment of the disk drive of the present invention over the full stroke of the actuator movement from the inner diameter to the outer diameter of the disk. 
     FIGS. 22-23 are graphs representing the relative magnitude of the torque exerted on an actuator arm by the voice coil motor of the second embodiment of the disk drive of the present invention over the full stroke of the actuator&#39;s movement. 
     FIG. 24 is a graph representing the relative magnitude of the torque exerted on an actuator arm by the voice coil motor of the third embodiment of the disk drive of the present invention over the full stroke of the actuator&#39;s movement. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Disk drives according to the present invention will be described with reference to FIGS. 1-24. The disk drives described herein include, for example, one or two hard disks with a magnetic coating and utilize Winchester technology; however, the disk drive of the present invention may utilize various numbers of disks and other types of disks, for example, optical disks, and other read/write technologies, for example, lasers. The diameter of the disks utilized in the disk drive of the present invention have a diameter on the order of 3.75 inches, or so-called “3½” disks; the disk drive of the present invention can be implemented with disks of other diameters whether larger or smaller than 3.75 inches. 
     A disk drive in accordance with either the first, second, or third embodiments of the present invention has the following outline dimensions: Height 1.0″ (2.54 cm); Length 5.75″ (14.61 cm); and Width 4.0″ (10.16 cm). The total weight is slightly over one (1) pound; for the first embodiment, 1.3 lbs (0.59 kg) for the second embodiment, and 1.16 lbs for the third embodiment. Thus, the disk drive of the present invention is one-half (½) of the size of a one-half (½) height 5¼″ inch disk drive. Importantly, the disk drive of the present invention weight approximately ⅓ to ½ of the weight of standard 3½″ disk drives of 20 Mb capacity. Even greater proportional reductions are provided when the first embodiment is formatted for 40 Mb capacity, and the second embodiment is formatted for 120 Mb capacity, and the third embodiment is formatted with a storage capacity of approximately 213 Mb, without any change in size or weight. 
     Although not to scale, FIGS. 1,  14 , and  15  illustrate the relationship between the length, width, and height of the disk drive; and thus low profile of the disk drive. In particular, the height “h” of the disk drive of the present invention is one inch (1″) 
     First Embodiment and Common Features 
     One feature of the first embodiment which provides the low height of the drive is the sloped profile of base plate  12  and cover  14 . The sloped profile provides extra vertical space below base plate  12  at the first end  10   a  of the disk drive and provides extra vertical space between base plate  12  and cover  14  at the second end  10   b  of the disk drive  10 . If the sloped profile were not provided, the amount of space allocated above and below base plate  12  would be the maximum amount of space provided at the respective first and second ends  10   a ,  10   b  of the disk drive  10 ; accordingly, the overall height of the disk drive would be increased. The cover  14  is sealably attached to base plate  12  to provide a controlled environment between base plate  12  and cover  14 . A gasket  16  (FIG. 4) between base plate  12  and cover  14  provides the seal. The ability to provide a controlled environment alleviates the need for a breather filter and allows the disk drive of the present invention to use an internal air filtration system. The seal provided by gasket  16  is stable, during operation of the disk drive, at pressures experienced at altitudes from 200 feet below sea level to 10,000 feet above sea level. 
     As Shown in FIG. 2 the internal components of the disk drive are separated into three interrelated groups: disk  20  and spin motor  22 , actuator assembly  24  for positioning heads  26  with respect to disk  20 , and header assembly  28  including header  30 , bracket  32 , reverse flex circuit  34  and coil  36  for pivoting latch arm  38 . 
     Actuator assembly  24  includes pivotal actuator arm  40 , heads  26  (FIG. 4) mounted at a first end of actuator arm  40 , an actuator coil  42  mounted at a second end of actuator arm  40  on the opposite side of the pivot point from the first end of the actuator arm, and a magnet structure  44 . Magnet structure  44  supports magnets  46  (FIG. 4) and its components, as described in detail below, are formed of magnetically permeable material to provide returns for the magnetic field generated by magnets  46 . The magnet structure  44  and actuator coil  42  are arranged so that a current in coil  42  passes through the magnetic fields created by magnets  46  to create a force which pivots actuator arm  40 . Currents passing in opposite directions of coil  42  create torques in opposite directions and pivot actuator arm  40  to position heads  26  at all locations between and including inside and outside diameters  48  and  50  of disk  20 . 
     In a conventional disk drive utilizing a voice coil, a flex circuit is provided to the region between header  30  and actuator arm  40 . Reverse flex circuit  34  curves toward the disk, thereby allowing latch coil to be placed between header  30  and actuator arm  40 . 
     A printed circuit assembly (or control means)  52  is attached to the bottom of base plate  12 . Header  30  carries all of the electrical signals from the printed circuit assembly  52  to the controlled environment between base plate  12  and cover  14 . Header  30  has a minimum number of pins due to the fact that a DC motor requiring only three (3) leads is utilized. Such a motor is described in U.S. Pat. No. 4,876,491, entitled METHOD AND APPARATUS FOR BRUSHLESS DC MOTOR SPEED CONTROL, filed Jul. 1, 1986, inventors John P. Squires and Louis J. Shrinkle, assigned to the Assignee of the subject application. 
     The structure of the disk drive  10  of the present invention, which provides the disk drive with a low overall height, will be described with reference to FIG. 3, which is a cross-sectional view along line  3 - 3 ′ in FIG.  4 . As shown in FIG. 5, base plate  12  includes two rails  54   a  and  54   b  at first and second sides  12   a  and  12   b  of base plate  12 . Rails  54   a  are constructed so that the mounting surface  12   e  of the base plate  12  sits at an angle with respect to the plane of the surface on which rails  54   a  and  54   b  rest. This angled relationship of base plate  12  and the support surface provides more room below base plate  12  at the first end  12   a  of the base plate than at the second end  12   b  of the base plate. Only a small amount of space is necessary for printed circuit assembly  52 , including the components mounted thereon; however, it is necessary to provide a connector  56  and a power plug on printed circuit assembly at the first end  12   a  of base plate  12  (FIG.  1 ), both of which require more vertical space than the printed circuit assembly  52 . The slope of base plate  12  provides the necessary vertical space for connector  56  and power plug  58  beneath the first end of the base plate  12   a . Connector  56  provides an interface between the printed circuit assembly  52  and a host computer (not shown) and power plug  58  provides an interface between printed circuit assembly  52  and an external power source (not shown). 
     Conversely, disk  20  is the only component located above the first end of the base plate  12   a , whereas the actuator assembly  24  is located above the second end of the base plate  12   b . Actuator assembly  24  requires more vertical space than disk  20  and the slope of base plate  12  provides more space above the second end of the base plate  12   b  than above the first end of the base plate  12   a  in order to accommodate the actuator assembly  24 . As shown in FIG. 1 the portion of cover  14  which meets with base plate  12  has an angle which corresponds to the angle of the base plate, and thus the top of the cover  14  is parallel with the support surface. Therefore, even though the base plate is sloped, the profile of the disk drive  10  is a rectangle as opposed to a parallelogram. 
     Disk  20  lies in a plane which is parallel to the support surface and which forms an angle with the plane of base plate  12 . All of the support points on the mounting surface  12   e  (FIG. 5) of base plate  12  are designed so that the internal components (e.g., actuator assembly  24 ) lie in plane parallel to the plane of disk  20  and the plane defined by support points  55  of rails  54   a ,  54   b.    
     The structure and operation of actuator assembly  24  will be explained with reference to FIGS. 4-7. The function of the actuator assembly  24  is to position heads  26  with respect to the surfaces of disks  20  by pivoting actuator arm assembly  40 . More specifically, to position the heads  26  over individual tracks on disk  20 . Heads  26  are supported on actuator arm  40  by flexures  60 . A bearing cartridge  62 , which is fixed to the base plate  12 , is inserted in actuator arm  40  to provide a pivot point. Actuator arm  40  is attached to bearing cartridge  62  by a clip ring  63 . Using clip ring  63  instead of epoxy allows the bearing cartridge  62  to be tested prior to assembly and cleaned independently of the actuator arm  40 . Actuator coil  42  is provided on actuator arm  40  on the opposite side of the pivot point from heads  26 . Actuator arm  40 , including all of the components attached thereto, is precisely balanced, i.e., equal amounts of weight are provided on either side of the pivot point so that the positioning of heads  26  is less susceptible to linear shock and vibration. 
     The force utilized to pivot arm assembly  40  is provided by a voice coil assembly. The voice coil assembly includes actuator coil  42  and magnet structure  44 . Magnet structure  44  comprises top and bottom plates  64 ,  66  formed of magnetically permeable material, support posts  68 ,  70  also formed of magnetically permeable material, and first and second magnets  46   a, b  attached to the top plate  64 . Top and bottom plates  64 ,  66  in conjunction with support posts  68 ,  70  function as returns for the magnetic fields provided by first and second magnets  46   a, b . It is important that there are no air gaps between support posts  68 ,  70  and either the top or bottom plate  64 ,  66 ; any air gap would create a discontinuity in the return, greatly reducing the strength of the magnetic field. 
     First and second magnets  46   a, b  have opposite poles attached to top plate  64  (i.e., the south pole of first magnet  46   a  and the north pole of magnet  46   b  are attached to the top plate  64 ) to provide first and second magnetic fields B 1 , B 2  between respective ones of the first and second magnets  46   a, b  and bottom plate  66 . First and second magnetic fields B 1 , B 2  are encompassed in three closed magnetic field loops. The first closed magnetic field loop extends between the first magnet  46   a  and bottom plate  66  and passes through a return provided by bottom plate  66 , first support  68 , and top plate  64 . The second closed magnetic loop passes from first magnet  46   a  to bottom plate  66 , through bottom plate  66  and between bottom plate  66  and second magnet  46   b , and from second magnet  46   b  to first magnet  46   a  via top plate  64 . The third closed magnetic loop extends between bottom plate  66  and second magnet  46   b  and passes through a return provided by top plate  64 , second support  70 , and bottom plate  66 . By containing the magnetic fields B 1 , and B 2 , in returns, the magnetic field intensity of each field is increased in the region between the respective first and second magnets  46   a, b  and bottom plate  66 ; the strength of the magnetic field in this region is directly related to the torque which the voice coil exerts on the actuator arm  40 , and thus the rotational velocity of actuator  40  and the seek times for the drive. 
     Actuator coil  42  is positioned so that it carries a current in opposite directions in first and second magnetic fields B 1 , and B 2 . 
     The force on a current carrying wire in a magnetic field is proportional to the magnetic field intensity, and is expressed by the equation F=id 1 ×B, where F is the force, i is the current,  1  is the length of the wire, and B is the magnetic field. Passing a current in opposite directions in actuator coil  42  provides respective forces F, and F 2  (FIG.  2 ); these forces F, and F 2  pivot actuator arm  40  in opposite directions. 
     Crash stops are provided to limit the pivoting movement of actuator arm  40  so that heads  26  travel only between selected inside and outside diameters  48 ,  50  of disk  20 . An outside diameter crash stop is provided by a sleeve  76  (FIG. 5) fitted on support post  68 . When the pivoting motion of actuator arm  40  places heads  26  at the outside diameter  50  of disk  20  a portion of the actuator arm  40  contacts outside diameter crash stop  76 , thereby preventing further movement of the heads  26 . An inside diameter crash stop is provided by the portion of the latch mechanism (FIG. 7) and is described below. 
     Reverse flex circuit  34  for carrying electrical signals from header  30  to heads  26  and actuator arm assembly  24  will be described with reference to FIGS. 2,  4 ,  6  and  7 . The reverse flex circuit is separated into three portions. A first portion  80  carries current to actuator coil  42 . A second portion  82  is a ground plane which separates the current carrying portion  80  from a third data-carrying portion  84 . The data carrying portion  84  provides signals to heads  26  for recording information on disk  20  and carries signals from the heads  26  to the printed circuit assembly  52 , via header  80 , when reading data from disk  20 . Interference with the relatively week data signals which would otherwise be caused by the larger currents necessary for actuator coil  42  passing through the first portion  80  of the reverse flex circuit  34  is prevented by the provision of ground plane  82 . 
     The reverse flex circuit  34  is electrically connected to pins  31   a  of header  30 ; however, pins  31   a  also serve to position the reverse flex circuit  34 . In particular, bracket  52  supports reverse flex circuit  34  and latch coil  36 . Bracket  32  is attached to base plate  12  by a single attachment point  86  and is rotationally positioned by the engagement of reverse flex circuit  34  and pins  31   a —the positioning of latch coil  36  being important to the operation of the latch mechanism as described below. A stiffener  88  is attached to reverse flex circuit  34  in the area where it engages pins  31   a  and is attached to bracket  32  to provide the rigidity necessary to rotationally position bracket  32 , and to facilitate engagement of reverse flex circuit  34  and pins  31   a . Reverse flex circuit  34  is parallel to the plane of base plane  12  in the region of header  31  but passes through a bend of approximately 90 degrees so that it forms the loop which extends towards disk  20  and connects header  30  to actuator assembly  24 . 
     First portion  80  of reverse flex circuit  34  terminates at the point where reverse flex circuit  34  joins actuator arm  40 ; however, the second and third portions  82  and  84  wrap around a shoulder  90  of actuator arm  40  which surrounds bearing cartridge  62 . Wrapping the second and the third portions  82  and  84  of reverse flex circuit  34  around shoulder  90  provides access to current-carrying wires are provided on the side of the flex circuit which faces the base plate in the region where reverse flex circuit  34  engages pins  31   a  of header  30 , and thus on the inside of the curved portion of reverse flex circuit  34  extending from bracket  32  to actuator arm  40 . As the first and second portions  82  and  84  wrap around shoulder  90 , the side of reverse flex circuit  34  on which the current-carrying wires are provided is exposed at the end of reverse flex circuit  34 , facilitating the attachment of wires  91  which connect heads  26  to reverse flex circuit  34 . If wires  91  were to be connected to reverse flex circuit  34  at the point where reverse flex circuit  34  first contacts actuator arm  40 , it would be necessary to wrap wires  90  around reverse flex circuit  34  or to provide connections through the reverse flex circuit  34 —both being more complex and less desirable manners of providing electrical connections between wires  91  and reverse flex circuit  34 . Any torque exerted on actuator arm  40  by any means other than the voice coil assembly affects the function of actuator assembly  24  in positioning heads  26  with respect to disk  20 , particularly the track following any seek functions described in the above referenced patents entitled DISK DRIVE SOFTWARE SYSTEM ARCHITECTURE and DISK DRIVE SOFTWARE SYSTEM ARCHITECTURE UTILITIES IMBEDDED REAL TIME DIAGNOSTIC MONITOR. The force provided by the voice coil assembly must be controlled to compensate for the force exerted by the reverse flex circuit  34 . Accordingly, the radius R (FIG. 7) of the curve in reverse flex circuit is made as large as possible to minimize the torque exerted on actuator arm  40  by reverse flex circuit  34 . Indeed, the radius of the curve in reverse flex circuit  34  is approximately twice as large as the radius in the curve of a conventional flex circuit. In addition, the reverse flex circuit  34  moves in an essentially linear manner when actuator arm  40  rotates, whereas a conventional reverse flex circuit must bend throughout its curve. Accordingly, the torque exerted on actuator arm  40  by reverse flex circuit is greatly reduced with respect to the torque exerted by a conventional flex circuit. 
     Another advantage provided by reverse flex circuit  34  is the ability to place latch coil  36  in a position where a conventional flex circuit would be located, and thus to integrate latch coil  36  with reverse flex circuit  34  and bracket  32 . Separate wires from header  30  to latch coil  36  are not necessary. Further, installing integrated group of components requires fewer steps than installing individual components. In addition, the critical positioning of latch coil  36  is provided by reverse flex circuit  34  and stiffener  88  controlling the pivotal position of bracket  32 , as described above. 
     All connections between the sealed environment between base plate  12  and cover  14  and printed circuit assembly  52  are provided by header  30 . Pins  31   a , which engage reverse flex circuit  34 , also engage motor wire connector  92 . Pins  31   b  extend below base plate  12  and engage a rear entry connector (not shown) on printed circuit assembly  52 . A rear entry connector is utilized because the integrated and discrete circuit components and the surface wirings are on the side of printed circuit assembly  52  facing away from base plate  12 . 
     A latch mechanism for locking the actuator arm  40  in an orientation where heads  26  are positioned at the inside diameter  48  of disk  20 , will be described with reference to FIGS. 4,  5  and  7 . During power-down of the disk drive  10  control means  52  causes actuator assembly  24  to pivot the actuator arm  40  to the position where the heads  26  are at the inside diameter of the disk over a non-data area of disk  20  before the rotational speed of the disk is decreased to the point where the heads  26  land on the disk  20 . Thus, the heads  26  land only on the non-data area at the inside diameter of the disk  20 . 
     The electromagnetic latch includes latch coil  36 , a latch arm  38  which pivots on pivot  94  and has a finger  96  for engaging latch notch  98  in actuator arm  40 , and a spring  100  for biasing the latch arm  38  to the locked position. 
     An electromagnet, including latch coil  36  and swivel plate  104 , is used to pivot latch arm  38  to the unlocked position against the force of spring  100 . Latch coil  36  includes a capture plate  106  having an outer wall  108  and a center pole  110 . The outer wall  108  and center pole  110  form opposite poles of an electromagnet, and when a current is passed through a coil (not shown) the magnetic field of capture plate  106  attracts swivel plate  104 ; swivel plate  104  is mounted on the latch arm  38  so that it can swivel in all directions and be flush with the outer wall  108  when the swivel plate  104  is captured by the electromagnet. Contact between the entire outer wall  108  and swivel plate  104  is necessary to provide reliability in the capture and retention of the swivel plate  104 . Center pole  110  of capture plate  106  is stepped so that only a small contact area exists between center pole  110  and swivel plate  104 ; this small contact area causes the latch coil  36  to release the swivel plate  104  when the current in the coil (not shown) is discontinued. A high DC voltage is applied to the latch coil  36  for a short time to capture the swivel plate  104 . Then, the applied voltage is reduced to a small capture maintenance level. Thus, this structure is low in power consumption and heat dissipation. Further, despite the low power consumption of the latch coil  36  it is highly reliable in its capture, holding, and release of swivel plate  104 . 
     Spring  100  is a linear spring engaging finger  96 . To reduce spring travel, thereby providing a constant and larger spring force, spring  100  is terminated outside the pivot point of pivot  94 . 
     Finger  96  also serves as the inside diameter crash stop. Finger  96  is well suited for the inside diameter crash stop because it is positioned to engage notch  98  which is at one edge of opening  102  in actuator arm  40 . The abutment of finger  96  and the same edge of opening  102  when the latch is unlatched provides the inside diameter crash stop. However, the pivoting movement of latch arm  27  in moving to the latched position reduced the distance between pivot  94  and the edge of opening  102 . Therefore, the actuator arm  40  pivots slightly to move the heads beyond the inside diameter  48  to a non-data area. 
     The above-described structure of the disk drive of the present invention provides excellent protection from shock and vibration. In particular, the disk drive will withstand nonoperating shocks of 200 g&#39;s and operating shocks, without nonrecoverable errors, of 5 g&#39;s. Nonoperating vibration of 2 g&#39;s in the range of 5-500 Hz is the specified tolerable limit. Operating vibration, without nonrecoverable data, is specified at 0.5 g&#39;s for the range of 5-500 Hz. 
     The disk  20  has 752 tracks per surface due to the ability of the actuator assembly  24  to operate with a track density of 1150 tracks per inch. Thus, utilizing 26 blocks per track and 512 bytes per block, the disk drive of the first embodiment has a formatted capacity of 20 MBytes. The actuator assembly  24  provides an average seek time of 28 ms and a track-to-track seek time of 7 ms. The average seek time is determined by dividing the total time required to seek between all possible ordered pairs of track addresses by the total number of ordered pairs addressed. 
     The assembly of the disk drive  10  of the present invention requires less steps than assembly of conventional disk drives. The spin motor  22  and disk  20  are attached to base plate  12 . Then, an integrated actuator group, including actuator arm  40 , bracket  32 , reverse flex circuit  34 , and latch coil  36 , all previously assembled, is installed. Magnet structure  44  is then placed on one of its attachment points and pivoted into position so that the portion of actuator arm  40  holding actuator coil  42  extends between the top and bottom plates  64 ,  66  of the magnet structure  44 . Latch arm  36  is then placed on its pivot point. The disk  20  is then pack written, and thereafter cover  14  is attached. Finally, printed circuit assembly  52  is attached outside of the clean room. 
     Second Embodiment 
     A disk drive  200  in accordance with the second embodiment of the present invention will be described with reference to FIGS. 8-12. 
     As shown in FIGS. 8-10, the construction of disk drive  200  includes a base  212  and a cover  214 . Gasket  216  provides a sealed, controlled environment between base  212  and cover  214 . First and second disks  220 ,  221  are supported on base  212  and rotated by spin motor  222 . Motor  222  is mounted in a well  223  in base  212 , thereby allowing lower disk  221  to be as close as possible to the top surface of base  212 . 
     An actuator assembly  224  positions heads  226   a-d  with respect to disks  220  and  221 ; heads  226   a  and  226   b  read information from and write information to respective, opposed surfaces of disk  220 , and heads  226   c  and  226   d  read information from and write information to respective, opposed surfaces of disk  221 . Tables 1 and 2 below specify certain characteristics of disks  220  and  221  and heads  226   a-d . 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 Number of Disks 
                 2 
                   
               
               
                   
                 Number of Data Surfaces 
                 4 
                   
               
               
                   
                 Number of Data Cylinders 
                 1522 
                 cylinders 
               
               
                   
                 (Tracks per surface) 
               
               
                   
                 Sectors per Track 
                 40 
                 physical 
               
               
                   
                   
                 39 
                 accessible 
               
               
                   
                 Bytes per Sector 
                 662 
               
               
                   
                 Data Bytes per Sector 
                 512 
                 bytes 
               
               
                   
                 Data Capacity per Data 
                 30 
                 Mbytes 
               
               
                   
                 Surface (formatted) 
               
               
                   
                 Total Data Capacity (formatted) 
                 120 
                 Mbytes 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
             
               
                   
                 Disk Diameter 
                 95 
                 millimeters 
               
               
                   
                   
                 3.74 
                 inches 
               
               
                   
                 Data Track Band Width 
                 20.32 
                 millimeters 
               
               
                   
                   
                 0.8 
                 inches 
               
               
                   
                 Track Density 
                 1850 
                 tracks/inch 
               
               
                   
                 Bit Density (max) 
                 23,800 
                 fci 
               
               
                   
                   
               
             
          
         
       
     
     Controller  227 , including printed circuit board  28  and circuitry  229  mounted on circuit board  228 , provides control signals to spin motor  222  and actuator assembly  224 , and provides data signals to and receives data signals from heads  226   a-d . Header  230  provides all electrical connections between controller  227  and the environment between base  212  and cover  214 . Header  230  comprises conductive pins  231  embedded in a plastic header  232  which is then potted in base  212 . A reverse entry connector  237  mounted on the front side  228   a  of printed circuit board  228  receives pins  231 ; pins  231  pass through printed circuit board  228  to enter connector  236 . Bracket  232  supports a flex circuit  233 , including a reverse flex circuit loop  234 , and connector  236  which provides electrical interconnections between flex circuit  233  and pins  231 . 
     With reference to FIG. 12, actuator assembly  224  includes pivotable actuator arm  240  and an actuator motor. The actuator motor is a so-called voice coil motor comprising coil  242  (provided on actuator arm  240 ), first and second magnets  246   a ,  246   b , top plate  264 , bottom plate  266 , first support post  268 , and second support post  270 . Top and bottom plates  264  and  266 , in conjunction with first and second support posts  268 ,  270  create returns for the magnetic fields provided by first and second magnets  246   a  and  246   b . The operation of the voice coil motor is described above with respect to the first embodiment. 
     The structure which enables disk drives  200  of the second embodiment of the present invention to include 2 disks,  220  and  221 , lying in parallel planes within a one inch height form factor disk drive will be described with reference to FIGS. 8-10. In the first embodiment of the present invention the sloped profile of base  12  allowed the use of a fully shrouded power connector  58 . In particular, power connector  58  was provided at the first end  10   a  of disk drive  10  where the sloped profile provided more room underneath base  12  and less room between base  12  and the top of cover  14 . In the second embodiment, base  212  has first and second side rails  213   a  and  213   b , and the mounting surface of base  212  is parallel to the plane defined by support points  215   a-g . The space below base  212  is the same at both ends of drive  200 ; in the second embodiment a sloped profile is not utilized. In comparison with the first embodiment, the uniform height of rails  213   a  and  213   b  is the same as the height to rails  54   a  and  54   b  at the second end  10   b  of drive  10 . Accordingly, the space between base  212  and cover  214  is increased at the end of drive  200  where disks  220  and  221  reside. This increased space between base  212  and cover  214 , combined with the placement of motor  222  in well  223 , allows two disks  220  and  221  to be provided in substantially parallel planes. 
     Printed circuit board  228  is mounted to base  212  by screws  254   a-c , and an insulating sheet  255  is provided between printed circuit board  117  and base  212  to prevent short circuiting of the solder points appearing on the back side  228   b  of printed circuit board  228  which faces base  212 . Printed circuit board  228  has an opening  253 , and well  223  protrudes through opening  253 . 
     The reduced height of rails  213   a  and  213   b  at the end of drive  200  where interface connector  256  and power connector  258  reside required for the removal of part of the shrouding from power connector  258 . Thus, pins  259  of electrical connector  258  are not protected by shroud  260  in the region between pins  259  and base  212 . However, because the connector which attaches to pins  259  is itself insulated, there is no danger of shorting pins  259  to base  212 . A third connector  257 , used for test purposes, is provided at the opposite end of drive  200  from connectors  256  and  258  as shown in FIG.  11 . 
     A latch mechanism for locking actuator arm  240  will be described with reference to FIGS. 11 and 12. The latch mechanism includes a magnet assembly  280  provided on second support post  270  and latch arm  282 , including latch finger  283 , mounted on actuator arm  240 . Magnet assembly  280  has a slot  284  and contains the magnetic field provided by a magnet (not shown) so that the magnetic field affects latch finger  283  only when latch finger  283  enters slot  284 . 
     A resilient element  285  provided in slot  284  of magnet assembly  288  functions as the inside diameter crash stop. A sleeve  288  provided on first support posts  268 , combined with tab  290  on actuator arm  240  function as the outside diameter crash stop. 
     Table 3 specifies certain performance characteristics of disk drive  200 . 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
             
             
               
                   
                 Seek Times 
                   
                   
               
               
                   
                 Track to Track 
                 8 
                 msec 
               
               
                   
                 Average 
                 sub-19 
                 msec 
               
               
                   
                 Maximum 
                 35 
                 msec 
               
               
                   
                 Average Latency 
                 8.8 
                 msec 
               
               
                   
                 Rotation Speed (±.1%) 
                 3399 
                 RPM 
               
               
                   
                 Controller Overhead 
                 1 
                 msec 
               
               
                   
                 Data Transfer rate 
               
               
                   
                 To/From Media 
                 1/5 
                 MByte/sec 
               
               
                   
                 Data Transfer Rate 
               
               
                   
                 To/From Buffer 
                 4.0 
                 MByte/sec 
               
               
                   
                 Interleave 
                 1-to-1 
                   
               
               
                   
                 Buffer size 
                 64K 
                 byte 
               
               
                   
                   
               
             
          
         
       
     
     All seek times are determined for nominal d.c. input voltages. Average seek times are determined by dividing the total time required to seek between all possible ordered pair of track addresses by the total number of ordered pairs. 
     Table 4 specifies certain environmental characteristics of disk drive  200 . 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
             
             
               
                   
                 Temperature 
                   
               
               
                   
                 Operating 
                 5° to 55° 
               
               
                   
                 Non-operating 
                 −40° C. to 60° C. 
               
               
                   
                 Thermal Gradient 
                 20° C. per hour maximum 
               
               
                   
                 Humidity 
               
               
                   
                 Operating 
                 8% to 80% non-condensing 
               
               
                   
                 Non-operating 
                 8% to 80% non-condensing 
               
               
                   
                 Maximum Wet Bulb 
                 26° C. 
               
               
                   
                 Altitude (relative to sea level) 
               
               
                   
                 Operating 
                 −200 to 10,000 feet 
               
               
                   
                 Non-operating (max.) 
                 40,000 feet 
               
               
                   
                   
               
             
          
         
       
     
     Table 5 specifies shock and vibration tolerances for disk drive  200 . Shock is measured utilizing a ½ sine pulse, having a 11 msec duration, and vibration is measured utilizing a swept sine wave varying at 1 octave per minute. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
             
             
               
                   
                 Non-operating shock 
                 75 G&#39;s 
               
               
                   
                 Non-operating vibration 
               
               
                   
                  5-52 Hz 
                 0.020″ (double amplitude) 
               
               
                   
                 63-500 Hz 
                 4 G&#39;s (peak) 
               
               
                   
                 Operating shock 
                 5 G&#39;s (without non-recoverable 
               
               
                   
                   
                 errors) 
               
               
                   
                 Operating vibration 
               
               
                   
                  5-27 Hz 
                 .025″ (double amplitude) 
               
               
                   
                 28-500 Hz 
                 .5 G&#39;s (peak) 
               
               
                   
                   
                 (without non-recoverable errors) 
               
               
                   
                   
               
             
          
         
       
     
     Third Embodiment 
     A disk drive  300  in accordance with the third embodiment of the present invention will be described with reference to FIGS. 13-24. 
     As shown in FIGS. 13-20, the construction of disk drive  300  includes a base  312  and a cover  314 , both generally formed of aluminum. Gasket  316  provides a sealed, controlled environment substantially isolated from ambient atmospheric pressures between base  312  and cover  314 . As will be discussed in further detail below, a unique, elastomeric and metal gasket provides improved sealing of the disk drive in accordance with the third embodiment. First and second disks  320 ,  321  are supported on base  312  and rotated by spin motor  322 . Motor  322  is mounted in a well  323  in base  312 , thereby allowing lower disk  321  to be as close as possible to the top surface of base  312 . 
     Basket  316  is formed to have a unique elastomeric and metal structure which provides improved sealing characteristics for disk drive  300  and ease of assembly. Generally, hermetically sealed disk drives utilize gaskets formed entirely of an elastomeric material. As shown in FIGS. 13 and 19, gasket  38  includes a metal layer  317  sandwiched between two elastomeric layers  318   1  and  318   2 . In one embodiment, layer  317  is formed of stainless steel and layers  318   1  and  318   2  are formed of burtyl rubber. The structure of gasket  316  provides easier assembly in the manufacture of drive  300  since the stiffness provided by the metal layer allows easier seating of the gasket structure on the base plate than drives using a purely elastomeric gasket. Gasket  316  further provides a seal for the hermetically sealed, controlled environment between cover  314  and base  312 . In this regard, gasket  316  has a lateral strength superior to that of purely elastomeric gaskets. The additional stiffness, yielded through the use of a high modulus material, such as burtyl rubber, in conjunction with the stainless steel sandwiched layer, improves the drive&#39;s resistance to a phenomenon known as “blow out”, which can cause a conventional elastomeric gasket of a hermetically sealed drive to deform with changes in external pressure relative to the pressure within hermetically sealed environment. 
     An actuator assembly  324  positions heads  326   a-d  with respect to disks  320  and  321 ; heads  326   a  and  326   b  read information from and write information to respective, opposed surfaces of disk  320 , and heads  326   c  and  326   d  read information from and write information to respective, opposed surfaces of disk  321 . Disks  320 ,  321  may comprise plated magnetic disks with an intensity of 1400 Oe. Table 6 below specifies certain characteristics of disks  320  and  321  and heads  326   a-d . Heads  326   a - 326   d  may comprise thin film, air bearing heads capable of operating at a minimum flying height of 4.3 micro-inch, with a gap width of approximately 7.5 micron, a gap length of approximately 0.4 micron, with a head gram load of approximately 5 grams. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
             
             
               
                   
                 Number of Disks 
                 2 
                   
               
               
                   
                 Number of Data Surfaces 
                 4 
                   
               
               
                   
                 Number of Data Cylinders 
                 2124 
                 cylinders 
               
               
                   
                 (Tracks per surface) 
               
               
                   
                 Sectors per Track 
                 50 
                 physical 
               
               
                   
                   
                 49 
                 accessible 
               
               
                   
                 Bytes per Sector 
                 668 
                 bytes 
               
               
                   
                 Data Bytes per Sector 
                 512 
                 bytes 
               
               
                   
                 Data Capacity per Data 
                 53.3 
                 Mbytes 
               
               
                   
                 Surface (formatted) 
               
               
                   
                 Total Data Capacity (formatted) 
                 213.2 
                 Mbytes 
               
               
                   
                 Disk Diameter 
                 95 
                 millimeters 
               
               
                   
                   
                 3.74 
                 inches 
               
               
                   
                 Data Track Band Width 
                 0.84 
                 inches 
               
               
                   
                 Track Density 
                 2496 
                 tracks/inch 
               
               
                   
                 Bit Density (max.) 
                 30,452 
                 fci 
               
               
                   
                   
               
             
          
         
       
     
     Controller  327 , including printed circuit board  328  and the circuitry mounted thereon provides control signals to spin motor  322  and actuator assembly  324 , and provides data signals to and receives data signals from heads  326   a-d , actuator assembly  324  and spindle motor  322 . Header  330  provides all electrical connections between controller  327  and the environment between base  312  and cover  314 . Header  330  comprises conductive pins  331  embedded in a plastic header  335  which is then potted in base  212 . Bracket  332  supports a flex circuit  333 , including a reverse flex circuit loop  334 , and connector  336  which provides electrical interconnections between flex circuit  333  and pins  331 . 
     Controller  327  may incorporate the system described in the above co-pending application entitled MULTIPLE MICRO CONTROLLER HARD DISK ARCHITECTURE. The third embodiment of the present invention provides a substantial increase in storage capacity within the same physical form factor as the drives of the first and second embodiments by incorporating several different factors. Specifically, the read/write heads used in the present invention, while being of the conventional air-bearing design, utilize a so-called 70% slider, wherein the dimensions of the head and slider have been reduced by approximately 30% from the sliders utilized in the first and second embodiments of the disk drive. In addition, the head gap width has been reduced to approximately 7.5 micron, with a gap length of 0.4 micron. In addition, with an increase in the intensity of the storage media to a 1400 Oe plated disk, and an increase in track density to 2496 tracks per inch, the aforementioned controller architecture allows for an increase in the storage capacity of the disk drive to up to about 213 MBytes, using 49 user sectors and providing a data rate of 20 MBytes/second. 
     Printed circuit board  328  is mounted to base  312  by mounting screws (not shown), and an insulating sheet (not shown, similar to sheet  255 ) may be provided between printed circuit board  328  and base  312  to prevent short circuiting of the solder points appearing on the back side  328   b  of printed circuit board  328  which faces base  312 . Printed circuit board  328  has and opening  353 , and well  323  protrudes through opening  353 . 
     The disk drive of the third embodiment has a structure, which is similar to disk drive  200  of the second embodiment  60 , that enables two (2) disks,  320  and  321 , to lie in parallel planes within a one inch height, three and one-half inch form factor disk drive. In the first embodiment of the present invention the sloped profile of base  12  allowed the use of a fully shrouded power connector  58 . In the third embodiment, as in the first embodiment, base  312  have first and second side rails  313   a  and  313   b , and the mounting surface of base  312  is parallel to the plane defined by support points  315   a-g . The space below base  312  is the same at both ends of drive  300 ; thus, in the third embodiment a sloped profile is not utilized. As with the second embodiment of the disk drive of the present invention, the placement of motor  322  in well  323  allows two disks  320  and  321  to be provided in substantially parallel planes. 
     Printed circuit board  328  may include an interface connector, power connector, and test connector similar to that utilized in the second embodiment of the drive of the present invention. 
     The specific structure, operation, and features of actuator assembly  324  will be explained with reference to FIGS. 14-18 and  20 . The function of the actuator assembly  324  is to position heads  326  with respect to the surfaces of disks  320 ,  321  by pivoting actuator arm assembly  340 , and more specifically, to position the heads  326  over individual tracks on disks  320 ,  321 . Heads  326  are supported on actuator arm  340  by load beams  360 . A bearing cartridge  362 , which is fixed to the base plate  312  at mounting region  312   a , is inserted in actuator arm  340  to allow arm  340  to rotate about pivot point “A” (FIG.  20 ). Actuator arm  340  is attached to bearing cartridge  362  by a clip ring  363 . As noted above, using clip ring  363  instead of epoxy allows the bearing cartridge  362  to be tested prior to assembly and cleaned independently of the actuator arm  340 . Heads  326  may thus be positioned along an arcuate path at any individual data track between innermost data track  295  and outermost data track  296  by the voice coil motor as described below. 
     The force utilized to pivot arm assembly  340  is provided by a so-called voice coil motor comprising coil  342  (provided on actuator arms  340 - 1 ,  340 - 2 ), first and second magnets  346   a ,  346   b , top plate  364 , bottom plate  366 , support post  368 , and latch body  370 . Actuator assembly  324  provides a unique coil and magnet design which improves the efficiency of the actuator by providing a relatively constant amount of torque on arm  340  throughout its rotational movement. Top and Bottom plates  364  and  366 , in conjunction with first support post  368  and latch body  370  create returns for the magnetic fields provided by first and second magnets  346   a  and  346   b . (The general operation of the voice coil motor is described above with respect to the first and second embodiments.) It is important that there are no air gaps between support posts  368 , latch body  370  and either the top or bottom plate  364 ,  366 ; any air cap would create a discontinuity in the return, greatly reducing the strength of the magnetic field. 
     First and second magnets  346   a ,  346   b  are bipolar, each having a first and second region  346   1 ,  346   2  with opposite poles attached to top plate  364  (e.g., the south pole of first magnet  346   a  and the north pole of second magnet  346   b  are attached to top plate  364 ) to provide first and second magnetic fields B 1 , B 2 , between respective ones of the first and second magnets  346   a ,  346   b  and bottom plate  366 . First and second magnetic fields {right arrow over (B)} 1 , {right arrow over (B)} 2  are encompassed in a closed magnetic field loops provided by top plate  364 , bottom plate  366 , support post  368 , and latch body  370 . 
     Actuator coil  342  is positioned so that it carries a current in opposite directions in first and second magnetic fields {right arrow over (B)} 1 , {right arrow over (B)} 2 . The strength of the magnetic field in this region between magnets  346   a ,  346   b  is directly related to the torque which the voice coil exerts on the actuator arm  340 , and thus the rotational velocity of actuator  340  and the seek times for the drive. 
     The force on a current carrying wire in a magnetic field is proportional to the magnetic field intensity, and is expressed by the equation {right arrow over (F)}={right arrow over (i)}dl×{right arrow over (B)}, where F is the force, i is the current, l is the length of the wire, and B is the magnetic field. Passing a current in opposite directions in actuator coil  342  provides respective forces {right arrow over (F)} 1 , and {right arrow over (F)} 2  (FIG.  17 ); these forces {right arrow over (F)} 1 , and {right arrow over (F)} 2  pivot actuator arm  340  in opposite directions about and axis passing through the center of bearing assembly  362 . 
     Actuator arm  340  may be fabricated of magnesium, including all of the components attached thereto, is precisely balanced, i.e., equal amounts of weight are provided on either side of the pivot point so that the positioning of heads  326  is less susceptible to linear shock and vibration. 
     Testing of the voice coil motors of conventional disk drives has shown that the magnetic field strength at the peripheral portions of actuator magnets is less than the magnetic field strength at the central portion of actuator magnet. Presumably, this is because the direction of magnetic flux between plates  364 ,  366  near the central portion of magnets  346   a ,  346   b  is essentially vertical, as shown in FIG. 16 by magnetic field {right arrow over (B)} 1 , and {right arrow over (B)} 2 . As one moves outward from the line of division between regions  346   1  and  346   2  toward the periphery of the magnet (sides  347 - 1  and  347 - 2 ), the direction of the magnetic flux tends to become non-perpendicular with respect to the surface of magnets  346   a ,  346   b . This has the effect of reducing the torque exerted by the voice coil motor on the actuator arm  340  when the arm is moving toward the innermost track  295  or outermost track  296 . FIGS. 21,  22 , and  23  show that the torque generated by the voice coil motor in the first (FIG. 21) and second (FIGS. 22-23) embodiments of the present invention decreases as actuator arm  340  positions heads  326  at inside diameter track  295  and outside diameter track  296 . FIG. 21 is a graph of the torque applied to actuator arm  40  of the disk drive of the first embodiment of the present invention upon acceleration of arm  40  in response to a seek command from controller  28 . As shown in FIG. 21, the loss recorded at the inside and outside diameter position of heads  26  is approximately 6% for the drive tested. Experimental results on a number of similar drives a typical loss at the inside and outside diameters of approximately 10%. 
     FIGS. 22 and 23 are graphs showing the relationship between the torque applied on acceleration of the actuator arm  240  of the disk drive of the second embodiment of the present invention in relation to the position of heads  226  at the inside and outside diameter tracks of disk  220 . As shown therein, the two drives tested show losses at the inside and outside diameters of the disk of approximately 12% and 10% respectively. 
     To provide a greater efficiency for the actuator of the third embodiment of the present invention, coil  324  and magnets  346   a ,  346   b  have been designed to provide both a greater effective area of coil  324  in the presence of magnetic field {right arrow over (B)} 1  and {right arrow over (B)} 2 , and a greater magnetic field intensity at the peripheral edges of the magnets. 
     FIG. 20 details the relationship between coil  324  and actuator magnet  346   b  as such, top plate  364  has been removed. It should be generally understood that the following principles, described in conjunction with magnet  346   b , apply equally to magnet  346   a  provided on top plate  364 . In order to compensate for torque losses at the inner diameter and out diameter, the surface area of magnet  346   b  is appreciably increased with respect to the actuator magnets shown in the first and second embodiments of the present invention. Specifically, magnet  346   b  includes a greater surface area at the respective ends  347 - 1  and  347 - 2  of the magnet, over which coil portions  324   1  and  324   2  are positioned when heads  326  are at inside diameter  295  or outside diameter  296  of disk  320 . The curvature of magnet edge  348 , positioned closest the axis of rotation of actuator body  340 . The arcuate shape of magnet edge  348  is such that it has a near tangential relationship with respect to edges  324   3  and  324   4  of coil  324 , and is defined to have constant radius “X” with respect to “B”, adjacent magnet  346   b . In one configuration, radius “X” is approximately 0.387 inch. Magnet  346   b  also includes an outer edge  345 , comprising first and second edges  345 , and  345   2 , meeting, at an angle, at the division of regions  346   1  and  346   2  of magnet  346   b . As will be noted from an examination of FIG. 12, only the linear, uncurved portions of coil  242  overlie magnets  346   a  and  246   b  in the second embodiment. In the third embodiment of the present invention, coil  324  has been modified so that more coil area is provided over the major surface of magnet  346 . Specifically, in the disk drive of the second embodiment of the present invention, approximately 35% of the coil area is utilized; in the third embodiment, coil area utilization is increased to approximately 43%. Thus, a greater amount of coil area is provided in magnetic fields B 1  and B 2 , therefore providing greater efficiency in the voice coil motor of the third embodiment of the present invention and greater torque on actuator arm  340 . Specifically, it is estimated that, due to both the improvement in the shape of magnets  346   a ,  346   b  and the shape of coil  342 , having a small curved area close to actuator pivot point “A”, the usable area of the coil is increased in this embodiment to approximately 43%. Further, because of the increased field strength provided by the greater surface area of magnet  346   b  near magnet ends  347 - 1  and  347 - 2 , the drop off associated with the acceleration torque in the first and second embodiments of the present invention is reduced. As shown in FIG. 24, the acceleration torque has a greater “linearity” than the acceleration torque shown in FIGS. 21-23. That is, the torque profile of the voice coil motor of the third embodiment is nearly linear between the inner diameter and the outer diameter, exhibiting less of an arcuate shape than the profiles depicted in FIGS. 21-23. Magnetic flux and torque loss associated with the positioning of the heads at the inner or outer diameters is markedly reduced, resulting in a total loss of torque of about 3% for the drive tested with respect to FIG.  24 . 
     The actuator design of the third embodiment of the present invention results in an improvement of approximately 4.7% in access time. 
     Generally, the seek time specification for hard disk drives is determined in relation to the drive&#39;s minimal expected efficiency. That is, in conventional drives, the lowest actuator torque constant (K t ) for a given drive between the innermost track and the outermost track of the disk is used to generate the expected seek profiles for the drive. Losses occurring primarily at the peripheral edges of actuator magnets create longer seek times. The benefits of the higher torque magnitudes, generated over the central areas of the magnet, is lost. 
     Actuator disk access is generally divided into three segments controlled by the control means: a full acceleration of the actuator toward the track; a controlled deceleration of the actuator to a point within a specified area near the track (typically ¼ track width); and a positioning loop, for accurately locating the head over the desired track, also known as “settling. The raw average access time is defined as comprising the acceleration and deceleration of the actuator. The effective improvement in average access time can be shown mathematically as follows. The raw average access time for a drive, such as that shown in FIGS. 13-20, is given by:        T   =       [     1   +     Va   Vd       ]              2      θ                 s     Kt            JR   Va                              
     where 
     θ s =the distance, in radians, of travel from start to finish for the actuator (typically ⅓ of a full stroke, 0.07 rad); 
     J=the polar inertia of a moving actuator (23.0×10 −6  in-lbs 2 ); 
     R=the resistance, in ohms, of the coil (25Ω); 
     K t =the motor torque constant (typically 0.7 in-lb/amp); 
     V a =the voltage applied to accelerate the actuator (9.5 v); and 
     V d =the voltage applied to decelerate the actuator (5 v). For purposes of clarity, the above equation neglects the effects of coil inductance, back EMF and assumes a controlled deceleration. 
     Given the above values, the total computed access time is 10.09 ms. By improving the torque constant, e.g., the “linearity” of the magnetic field over the fall stroke of the actuator arm, and improvement in access time for the drive will follow, as shown in the following analysis. 
     By holding all variables except K t  constant, the torque equation is simplified to:        T   =       K   1              K   2       K   t                                  
     where          K   1     =     1   +     Va   Vd             and             K   2     =       2      θ                 JR     Va       ,                          
     we find              T   =       K   1              K   2       K   t                       =       K   1            K   2            (     1       K   t         )                                    
     If K=K 1 {square root over (K 2 )}, then,        T   =     K        (     1       K   t         )                              
     If then, the torque constant K t  is increased by a factor of 10% so that              T   =     K        (     1       1.1                   K   t           )                   =     K   (     1       1.1          K   t             )                 =     .953                   K        (     1       K   t         )                                      
     Thus, for every 10% improvement in the torque constant, a 4.7% improvement in access time, T can be seen. 
     Hence, by increasing the total minimum torque constant by increasing surface area of the voice coil magnet and the area of the coil in the field generated by the voice coil magnets, the average seek times for the drive can likewise be decreased. 
     Crash stops are provided to limit the pivoting movement of the actuator arm  340  so that heads  326  travel only between selected inside and outside diameters  295 ,  296  of disk  320 . An outside diameter crash stop is provided by a sleeve  376  (FIGS. 16,  17 , and  20 ) fitted on support post  368 . When the pivoting motion of actuator arm  340  places heads  326  at the outside diameter  296  of disk  320  portion  242  of actuator arm  340 - 2  contacts outside diameter crash stop  376 , thereby preventing further movement of the heads  326 . An inside diameter crash stop is provided by the portion of the latch mechanism and is described below. 
     A latch mechanism for locking actuator arm  340  will be described with reference to FIGS. 14-20. 
     The latch mechanism of the third embodiment of the disk drive of the present invention utilizes the force of the voice coil actuator magnets  346   a  and  346   b  to provide the magnetic retentive force for the latching actuator  340 . 
     As can be seen in FIGS. 14-20, a capture pin  130  formed of magnetically permeable material is provided in latch arm  340 - 1 . Latch support structure  270  is designed so that the magnetic circuit formed by actuator magnets  346   a  and  346   b  provides a flux path through structure  270 . Voids  398 - 1  through  398 - 4  are formed in structure  270  to channel the magnetic flux from magnets  346   a  and  346   b  to air gap  399 . Specifically, air gap  399  has a width W of approximately 0.012 inches. Capture pin  130  is generally “T”-shaped, including portion  131  extending through a bore in actuator latch arm  340 - 1  and secured thereto by a snap ring (not shown). The magnetic flux provided by magnets  346   a  and  346   b  and channeled through support structure  270  exhibits a fringing effect when the flux encounters gap  399 . When actuator  340  is directed to position heads  326  over the landing zone at inner diameter  295 , capture pin  130  is drawn into abutment with tabs  398   a  and  398   b  of structure  270 . As pin  130  engages tabs  398   a ,  398   b , the magnetic flux provided by magnets  346   a  and  346   b  passes through pin  130 , making pin  270  part of the magnetic circuit formed by structure  270  and magnets  346   a ,  346   b.    
     The latching force provided by the latching mechanism is 50-60 inchgrams. The amount of latching force may be adjusted by providing a shunt  375  (FIG. 16) across gap  399  to provide a flux path in parallel with the flux fringing about gap  399 . Generally, there is no need for an additional latch magnet to provide the requisite magnetic latching and releasing forces for the actuator. Actuator assembly  324  can generate sufficient force to release actuator arm  340  from the latched position. The strength of the latching force is sufficient to retain the actuator in a captured position under non-operating shocks of up to 75 G&#39;s. 
     Table 8 specifies certain performance characteristics of disk drive  300 . 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 8 
               
               
                   
                   
               
             
             
               
                   
                 Seek Times 
                   
                   
               
               
                   
                 Track to Track 
                 3 
                 msec 
               
               
                   
                 Average 
                 12 
                 msec 
               
               
                   
                 Maximum 
                 25 
                 msec 
               
               
                   
                 Rotation Speed (±.1%) 
                 4491 
                 RPM 
               
               
                   
                 Data Transfer Rate 
               
               
                   
                 To/From Media 
                 20 
                 MByte/sec 
               
               
                   
                 Interleave 
                 1-to-1 
                   
               
               
                   
                   
               
             
          
         
       
     
     Table 9 specifies certain environmental characteristics of disk drive  300 . 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 9 
               
               
                   
                   
               
             
             
               
                   
                 Temperature 
                   
               
               
                   
                 Operating 
                 5° C. to 55° C. 
               
               
                   
                 Non-operating 
                 −40° C. to 60° C. 
               
               
                   
                 Thermal Gradient 
                 20° C. per hour maximum 
               
               
                   
                 Humidity 
               
               
                   
                 Operating 
                 8% to 80% non-condensing 
               
               
                   
                 Non-operating 
                 8% to 80% non-condensing 
               
               
                   
                 Maximum Wet Bulb 
                 26° C. 
               
               
                   
                 Altitude (relative to sea level) 
               
               
                   
                 Operating 
                 −200 to 10,000 feet 
               
               
                   
                 Non-operating (max.) 
                 40,000 feet 
               
               
                   
                   
               
             
          
         
       
     
     Table 10 specifies shock and vibration tolerances for disk drive  200 . Shock is measured utilizing a ½ sine pulse, having a 11 msec duration, and vibration is measured utilizing a swept sine wave varying at 1 octave per minute. 
     
       
         
               
               
               
             
           
               
                 TABLE 10 
               
               
                   
               
             
             
               
                 Non-operating shock 
                 75 G&#39;s 
                   
               
               
                 Non-operating vibration 
               
               
                 63-500 Hz 
                 4 G&#39;s 
                 (peak) 
               
               
                 Operating shock 
                 5 G&#39;s 
                 (without non-recoverable 
               
               
                   
                   
                 errors) 
               
               
                 Operating vibration 
                 .5 G&#39;s 
                 (peak) 
               
               
                   
                   
                 (without non-recoverable errors) 
               
               
                   
               
             
          
         
       
     
     The many features and advantages of the disk drive of the present invention will be apparent to those skilled in the art from the Description of the Preferred Embodiments. For example, those skilled in the art will appreciate that the structure of the disk drive of the present invention as described herein can be scaled for use with disk drives having disks with smaller and larger than 3½ inches. Thus, the following claims are intended to cover all modifications and equivalents falling within the scope of the invention.