Abstract:
A magnetic disc drive assembly comprises a disc drive housing having an external three-dimensional configuration matching a standard configuration. A disc drive is supported in the housing and includes a stack of rotatable rigid magnetic recording discs in a unique configuration wherein each disc has a diameter smaller than the diameter of rigid discs ordinarily contained in a disc drive housing having the standard configuration. Optionally, the stack of discs includes a number of discs greater than that normally housed in a disc drive housing having the standard configuration. Various techniques are employed to achieve the unique disc configuration, including a stop mechanism attached to the yoke of an E-block assembly, a conductor assembly electrically connecting transducers on the E-block to a flex circuit and employing fins supported in slots in the E-block, a cable connector mounted to a circuit board supported on the disc drive housing and having a connector housing conforming to a portion of the disc drive housing, and a desiccant housing providing structural support for the disc drive housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from U.S. Provisional Application No. 60/057,955, filed Sep. 5, 1997 for “Ultra High Performance Disc Drive” by Kent J. Forbord and from U.S. Provisional Application No. 60/063,322, filed Oct. 27, 1997 for “Ultra High Performance Disc Drive” by Kent J. Forbord. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to magnetic disc drive assemblies of the class employing a stack of rigid discs in a standard housing profile. 
     Magnetic disc drive assemblies employing rigid, or hard, discs are commonly used in desktop and other computer mainframes as a principal memory for the computer. Currently, rigid disc magnetic disc drive assemblies are available in three different standard footprints, commonly known as 2½ inch, 3½ inch and 5¼ inch drives. These standard drives are available in several configurations, the most common being known as low-profile and half-high drives. The principal difference between a low-profile drive and a half-high drive is that a low-profile drive typically has half the number of rigid discs in the disc stack, and hence half the data storage capacity, as a half-high drive. Computer manufacturers design their computer models to accommodate one of these three standard footprints and one of the two configurations. Consequently, disc drive manufacturers produce disc drives having a form and fit meeting the standard configuration of one of the three footprints and one of the two heights. 
     As used herein, the term “footprint” refers to the two-dimensional plan or layout of an element at a given plane, such as the mounting layout of the element. The “footprint” of a disc drive is, therefore, the two-dimensional plan of the disc drive housing at a given plane, such as its mounting layout within the computer. The term “real estate” as used herein, refers to the three-dimensional space or volume required by an element in its operational mode. “Real estate” also refers to the space or volume required to perform an operation. Therefore, the “real estate” required for an E-block assembly is the volume required for the E-block in its full rotational pattern, as well as any space required for its installation and routine repair. The term “configuration” as used herein, refers to the three-dimensional layout or plan of an element; the “configuration” of a disc drive being the three-dimensional layout or plan of the space taken by the disc drive housing. 
     There is a continuing need for faster computers with greater capacity. This need is met in the disc drive industry by a combination of factors, including increasing density of data recorded on discs, increasing data transfer rates between the disc and the electronics, shortening the seek time of movement of a transducing head to a desired track on a disc, and reducing the latency to reaching a desired location on a track, among others. With increasingly improved discs, it is possible to pack more data into a given area of a disc. With increasingly more precise transducing heads, it is possible to transduce data to and from high density discs. With increasingly improved circuits, it is possible to respond to data at higher data rates. With lighter and shorter actuator arms it is possible to reduce seek times for the transducing heads. With increasingly improved spindle motors, it is possible to spin the discs faster to thereby improve data rates and reduce latency. It will be appreciated, however, that certain trade-offs are required for a given configuration of disc drives. More particularly, shorter actuator arms require smaller discs, meaning there is less disc surface on which to record data. Increased disc speed requires more power, generating more heat which requires dissipation. Given the constraint that the overall profile of the disc drive housing must conform to one of the standards, as may be required by the computer manufacturer into which the drive is to be assembled, additional trade-offs may be required to accommodate the specifications for the computer manufacturer. 
     The present invention is directed to a disc drive having a standard housing configuration containing a stack of rigid recording discs that are rotated at increased speed without increasing the power consumption of the drive. The present invention is also directed to a disc drive having a standard housing configuration containing a stack of rigid recording discs having smaller than standard diameters without reducing the data capacity of the drive. The present invention is also directed to a disc drive having a standard housing configuration containing a stack of rigid recording discs having smaller than standard diameters and a shorter actuator arm for reduced seek times. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect of the invention, a magnetic disc drive assembly includes a disc drive housing having an external three-dimensional configuration matching a standard configuration. A disc drive is supported in the housing. The disc drive assembly includes a stack of rotatable rigid magnetic recording discs each having a diameter smaller than the diameter of rigid discs ordinarily contained in a disc drive housing having the standard configuration. The disc drive assembly also includes a head/actuator assembly for reading data to and writing data from selected ones of the discs. 
     In one embodiment of this aspect of the invention, the disc drive housing has a standard 3½ inch external three-dimensional configuration. The stack of rotatable rigid magnetic recording discs comprises discs having a diameter of 84 mm each. 
     In another embodiment of this aspect of the present invention, the number discs within the housing is greater than the number of discs ordinarily contained in the disc drive housing having the standard configuration. 
     In another embodiment of this aspect of the present invention, the magnetic disc drive assembly includes means for stacking and rotating the stack of rigid magnetic recording discs within the housing. Each disc has opposite recording surfaces. The head/actuator assembly includes a plurality of transducers, each associated with a recording surface of one of the discs, and actuator means supporting the plurality of transducers for positioning each transducer adjacent a respective surface of a disc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a standard magnetic disc drive, with the top cover removed, as in the prior art. 
         FIG. 2  is a partial section view of the disc stack and spindle assembly of the disc drive illustrated in  FIG. 1 , taken at line  2 — 2  in FIG.  1 . 
         FIG. 3  is a top plan view of a magnetic disc drive, with the top cover removed, in accordance with the present invention. 
         FIG. 4  is a partial section view of the disc stack and spindle assembly of the disc drive illustrated in  FIG. 3 , taken at line  4 — 4  in FIG.  3 . 
         FIG. 5  is a frontal and top perspective view of the disc drive illustrated in  FIGS. 3 and 4 , with the top cover removed. 
         FIG. 6  is an exploded perspective view, as in  FIG. 5 , of the disc drive illustrated in  FIGS. 3 and 4  and its top cover. 
         FIG. 7  is a perspective bottom view of the disc drive housing illustrated in  FIGS. 3 and 4  illustrating the assembly of the bottom seal to the housing. 
         FIG. 8  is a section view of the disc drive housing taken at line  8 — 8  in FIG.  3 . 
         FIGS. 9 and 10  are perspective views of opposite sides of a connector employed in the disc drive illustrated in  FIGS. 3 and 4 . 
         FIG. 11  is a plan view of a latch mechanism employed in the disc drive illustrated in  FIGS. 3 and 4 . 
         FIG. 12  is a perspective view of a portion of an actuator assembly of the disc drive illustrated in  FIGS. 3 and 4 . 
         FIG. 13  is an exploded perspective view illustrating connection of conductors between a flex circuit and transducing heads supported on load arm/gimbal assemblies of the actuator assembly illustrated in FIG.  12 . 
         FIG. 14  is a top view of the actuator assembly illustrated in  FIG. 12  with the conductors in place. 
         FIG. 15  is a perspective view of the complete actuator assembly of the disc drive illustrated in FIGS.  3  and  4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a top view, and  FIG. 2  is a section view taken at line  2 — 2  in  FIG. 1 , of a standard 3½ inch half-high disc drive as in the prior art. The disc drive includes a housing  10  having a standard footprint that is 101.6 millimeters (4.0 inches) wide and 146 mm (5.75 inches) long. A stack of discs  12  are mounted to a disc spindle  14  centered on an axis  16  that is located 50.8 mm (2.0 inches) from one short side  18  and both long sides  20  and  22  of housing  10 . Discs  12  have a diameter of 95 millimeters (3.74 inches) and are stacked on spindle  14  within a cylindrical receiver portion of housing  10  defined by inner cylindrical surface  24 . Surface  24  has a radius of approximately 48.3 mm (1.9 inches), centered on axis  16 . It will be appreciated that the thickness of the walls of housing  10  at the points where surface  24  is closest to the external sides  18 ,  20  and  22 , is about 2.5 mm (0.1 inches). 
     As shown particularly in  FIG. 2 , the stack of discs comprises ten concentric discs  12  mounted to an aluminum hub  26  by clamp ring  28 . Balance shims  30  positioned on the clamp ring and the lower portion of hub  26  provide balance to the stack of discs to prevent wobble as the discs spin. Each disc has a thickness of approximately 0.8 mm (0.0315 inch) and spacers  33  space the discs from each other by approximately 1.84 mm (0.0725 inch). As shown, spacers  33  extend radially from spindle axis  16  by a design width greater than the radial width of clamp ring  28 . The radial extent of spacers  33  define the position of the innermost track on discs  12 . The radius of the clamp ring is smaller than the radius of the spacers. The stack height of a full stack of ten discs (between the top surface of the top disc and the bottom surface of the bottom disc) is approximately 24.6 mm (0.9675 inch). Motor  32  is mounted to spindle  14  to rotate discs  12  at a design speed of 7200 revolutions per minutes (rpm). The disc drive illustrated in  FIGS. 1 and 2  has a track density of 8250 tracks per radial inch (325 tracks per radial millimeter) of each disc. With ten discs as described, the disc drive of the prior art has a data capacity of about 18 gigabytes. 
     Input/output cable connector  34  is a female connector that mates with a corresponding standard male connector (not shown) connected to external circuitry (not shown). Connector  34  is connected to circuit board  35  that nests beneath the disc drive at an underportion of housing  10 . Due to its configuration, connector  34  requires more space adjacent side  18  of the housing than board  35  requires more centrally. Connector  34  and circuit board  35  provide power and control inputs for motor  32  as well as signal and power inputs and outputs for other portions of the disc drive to be described. Circuit board  35  may also include data processing circuits used in reading and writing data from and to the recording surfaces on the discs. Typically, additional printed circuits (not shown) are formed in housing  10  on a bottom surface for distribution of signals to voice coil motor  36  ( FIG. 1 ) for E-block  38 , as well as to bulkhead connector  40 . Bulkhead connector  40  is connected to flex circuit  42 , which in turn spans the space and is connected to conductors on E-block  38 . The conductors on the E-block extend to magnetic transducing heads on sliders  44 , one slider being mounted to each load arm  46  at the end of the actuator arms of E-block  38 . Load arms  46  support gimbal suspensions that support head/slider devices. Slider  44  “flies” over the respective disc surface on an air bearing created by rotation of the disc. 
     As is well known in the art, there is a separate load arm  46  and gimbal/slider/head  44  for each of the twenty disc surfaces of the ten discs  12 . The twenty load arms  46  are mounted to eleven actuator arms of the E-block for rotation about axis  48  under the influence of voice coil motor  36 . A latch pin  50  is mounted to arm  52  of E-block  38  to react against stop surfaces (not shown) rigidly mounted to the lower wall or deck of housing  10  to limit the rotational travel of the E-block to thereby define the inner and outer tracks on discs  12 . The engagement of latch pin  50  to a stop surface limits the rotational travel of E-block  38  about the axis  48  of the actuator arm, thereby defining stop positions for the stop arm that in turn define the inner and outer tracks of the discs. In the prior art 3½ inch disc drive, the inner data track radius is 20.4 mm (0.804 inches) and the data outer track radius is 45.7 mm (1.8 inches) from spindle axis  16  of discs  12 . 
     Conveniently, a latch mechanism  56  is mounted to housing  10  to engage E-block  38  when the actuator assembly is in a rest or shipping position at an inner track of discs  12 . Latch mechanism  56  is mounted to the bottom wall of housing  10  in the space adjacent flex cable  42 . It will be appreciated that flex cable  42  requires a volume of space (real estate) to fold or bend within the housing as E-block  38  rotates to position the heads at selected radial positions relative to the discs. Desiccant package  68  is positioned between bulkhead connector  40  and side wall  22  of housing  10 . 
     A stainless steel cover  70  ( FIG. 2 ) is fastened to the top surface of housing  10  with a gasket  72  to thereby seal the contents of the housing and protect the disc drive from contaminants that might otherwise enter the drive. Conveniently, a desiccant packet  68  is inserted into the disc drive prior to final assembly of flex cable  42  and cover  70  to housing  10  to maintain the humidity within the disc drive to a design level. With the cover in place, the overall height of the disc drive is 41.15 mm (1.62 inches). 
     It will be appreciated that the space within housing  10  of the disc drive illustrated in  FIGS. 1 and 2  is occupied with the various parts of the disc drive. Real estate is at a premium, restricting optimal layout of additional electronics or mechanical features to improve the disc drive performance. 
     It will also be appreciated that the outer edges of the discs are moving at a linear rate of approximately 1,615 inches per second (ips) (63.58 mm/s). The relative movement of the disc to the transducer slider creates an air bearing on which the slider flies. However, the rotating disc also pumps air into and out of the space between the discs, creating a turbulent air flow pattern in that space. This turbulence creates varying air velocities and pressures within the disc drive which excite the disc assembly into resonance. Resonance within the disc assembly creates mechanical movements, resulting in transducer or head positioning errors which can adversely affect the performance of the disc drive or adversely limit track density. Baffles  60 ,  62 , and  64  are often employed about the outer periphery of the discs to channel air movement and reduce air turbulence within the disc drive, thereby reducing drag on the discs and the power required to rotate the discs. Conveniently, filter  66  may be employed to filter contaminants from the air. 
     A “low-profile” version of the disc drive illustrated in  FIGS. 1 and 2  comprises a disc drive with five discs (instead of ten in a half-high drive) so that the stack height is 11.37 mm (0.4475 inches), instead of 24.6 mm in a half-high drive, and the overall or profile height with the cover in place is 25.4 mm (1.00 inches), instead of 41.15 mm in a half-high drive. Also, since there are only five discs, ten load arms mounted to six actuator arms of the E-block are employed, instead of twenty and eleven in the case of the half-high drive. Otherwise, the construction is the same. The low-profile and half-high drives enjoy the same footprint, and the same size and style of recording discs, and essentially the same seek time. However, because there are half as many discs in a low-profile drive, the total data capacity is also half that of a half-high drive. Hence, the low-profile drive has a capacity of about 9 gigabytes, compared to 18 gigabytes of the half-high drive. 
     There are several problems with the disc drive illustrated in  FIGS. 1 and 2 . Due to the volume requirements of the various components of the drive, there is no real estate available for future electronic or mechanical features to improve the disc drive. Moreover, the drive is limited in access time and speed of recovery. More particularly, the actuator assembly illustrated in  FIG. 1  has a length of 52 mm (2.05 inches) from axis of  48  to the transducing gap of head  44 . The actuator arm illustrated in  FIG. 1  typically requires an inertia of 116 gram-cm 2  (18 gram-inch 2 ). Track seeks, which is the movement of the head from a current track to a desired destination track, requires an average of 7.7 milliseconds (msec). Moreover, once reaching the destination track, there is a latency associated with the disc drive because the disc must rotate to a position where the head may read a header or other informational portion of the track before the head is readied for transducing with the track. During the seek movement and latency, it is not possible to read data from, or write data to, the disc tracks. 
     The present invention is directed to an improved disc drive requiring less inertia for the actuator arm and a shorter average seek time without sacrificing drive capacity or the form factor of the disc housing, or significantly increasing power requirements of the spindle motor. The disc drive of the present invention requires less power to rotate a disc at a given speed. One form of the disc drive of the present invention achieves higher disc rotational velocities without significantly increasing power requirements of the spindle motor. Hence, the operating temperature of the drive is not increased. Since higher operating temperatures of a disc drive accelerates disc drive failure, the present invention achieves improved performance without increasing failure due to temperature. 
       FIGS. 3 and 4  illustrate a top view and section view of a disc drive  100  in accordance with one embodiment of the present invention.  FIG. 5  is a perspective view of disc drive  100 ,  FIG. 6  is an exploded top perspective view of disc drive  100 ,  FIG. 7  is an exploded bottom perspective view of the disc drive housing for disc drive  100 , and  FIG. 8  is a section view of the disc drive housing taken at line  8 — 8  in FIG.  3 . For sake of comparison, the disc drive illustrated in  FIGS. 3 ,  4  and  5 - 8  will be described in comparison to the 3½ inch half-high standard disc drive illustrated in  FIGS. 1 and 2 , but it is understood that the principles of the present invention are applicable to other standard disc drive forms, including 2½ inch and 5¼ inch drive forms and other heights, including low-profile. 
     Disc drive  100  includes a housing  102  having a standard footprint that is 101.6 mm (4.0 inches wide) and 146 mm (5.75 inches) long and identical to the footprint of the disc drive illustrated in  FIGS. 1 and 2 . A stack of twelve discs  104  are mounted to a disc spindle  106  centered on an axis  108  that is located 50.8 mm (2.0 inches) from one short side  110  and both long sides  112  and  114  of housing  102 . Discs  104  have a diameter of 84 millimeters (about 3.3 inches) and are stacked on spindle  106  within a cylindrical receiver portion of housing  102  defined by inner cylindrical surface  116 . Surface  116  has a radius of approximately 43.2 mm (1.7 inches), centered on axis  108 . It will be appreciated that walls  110 ,  112  and  114  form a lip  115  at the top of housing  102 , and that the thinnest portion of lip  115  (where surface  116  is closest to the external sides  110 ,  112  and  114 ), is about 7.6 mm (0.3 inches), as compared to 2.5 mm in the drive illustrated in  FIGS. 1 and 2 . Moreover, wall  110  includes heat fins  190  (FIG.  5 ), and the bottom edge of wall  110  includes a curved outline following the curve of the discs. 
     As shown particularly in  FIG. 4 , the stack of discs comprises twelve concentric discs  104  mounted to an aluminum hub  120  by clamp ring  122 . Balance shims  124  positioned on clamp ring  122  and the lower portion of hub  120  provide balance to the stack of discs to prevent wobble as the discs spin. Each disc  104  has a thickness of approximately 0.8 mm (0.0315 inch) and spacers  123  between the discs space the discs from each other by approximately 1.75 mm (0.069 inch). Consequently, the stack height of a full stack of twelve discs is approximately 28.88 mm (1.137 inch). Motor  126  is mounted to spindle  106  to rotate discs  104  at a design speed of 10,000 rpm. 
     Input/output connector  130  connects external circuitry (not shown) to circuit board  131  mounted under the underportion of housing  102 . Connector  130  is illustrated in greater detail in  FIGS. 5 ,  9  and  10 . Like connector  34  shown in  FIG. 2 , connector  130  requires more space at the edges of the housing than board  131  requires centrally. Connector  130  includes a housing  300  having an opening  302  for receiving an industry standard male plug connector (not shown) from a cable (not shown) connected to circuitry (not shown) external to the disc drive. Contacts  304  within opening  302  are arranged to mate with contacts (not shown) on the plug connector. Opening  306  receives an edge of circuit board  131  ( FIG. 4 ) and includes contacts  308  arranged to engage corresponding contacts on board  131 . The upper surface  310  of housing  300  includes an arcuate recess  312  having the same configuration as the curved bottom edge  111  ( FIG. 7 ) of wall  110  of housing  102 . Connector  130  does not interfere with the space required for discs  104  due to the smaller radius of discs  104  as compared to that of discs  12  of the prior art and recess  312  receiving the bottom edge of wall  110  of housing  102 . Consequently, the lowermost disc  104  closest to the lower wall of housing  102  is closer to the lower wall of the housing than is the lowermost disc of the stack of discs  12  shown in FIG.  2 . As in the prior art, connector  130  provides power and control inputs for motor  126  as well as signal and power inputs and outputs for other portions of the disc drive to be described. 
     As shown particularly in  FIG. 4 , the thickness of the bottom wall  125  of housing  102  is thinner than that of prior art housing  10 . More particularly, the thickness of the bottom wall  125  is about 3.25 mm (0.124 inches), compared to about 3.81 mm (0.150 inches) at bottom wall  31  in housing  10 . Surface  116  forms a reduced receiver portion within housing  102  to receive the smaller discs. This reduced receiver portion offsets any reduction in axial stiffness of housing  102  due to the reduced thickness of wall  125 . Additionally, the thicker walls  110 ,  112  and  114  as described above, and the structural support provided by desiccant housing  186  described below, provide additional structural support for housing  102 . 
     Also as shown in  FIG. 4 , clamp ring  122  is axially thinner, but radially wider, than clamp ring  28  shown in FIG.  4 . More particularly, the radial width of clamp ring  122  is approximately equal to the radial width of spacers  123  to compensate for the smaller axial thickness of the clamp ring to thereby control hoop stress in the clamp ring. The radial extent of spacers  123  define the position of the innermost track on discs  104 . The reduced thickness of wall  125  (compared to wall  31 ), thinner clamp ring  122  (compared to clamp ring  28 ), thinner spacers  123  (compared to spacers  33 ) and closer positioning of the disc stack to the lower wall of the housing permit the twelve discs of disc drive  100  to fit into the same vertical dimension as the ten discs of the disc drive according to the prior art. Hence, the disc drive shown in  FIG. 4  has a height of 41.15 mm (1.62 inches), the same as the disc drive shown in FIG.  2 . The structural integrity of clamp ring  122  is not affected because its extended radial width offsets its thinner axial thickness. Moreover, the position of the innermost radial track on the recording disc is not affected by the wider clamp ring because the clamp ring extends no further from spindle axis  108  than do spacer rings  123 . 
     Printed circuits (not shown) are formed in housing  102  on a bottom surface to provide connection to voice coil motor  140  ( FIG. 3 ) for E-block  142 , as well as data paths to bulkhead connector  170  mounted to the bottom wall of housing  102 . Flex circuit  172  is connected to connector  170  and to conductors  214  ( FIG. 13 ) on E-block  142  to provide signals to heads  144  mounted to each load arm  146  at the end of the actuator arms of E-block  142 . Flex circuit  172  also carries voice coil signals for motor  140 . 
     As is well known in the art, there is a separate load arm  146  and gimbal/slider/head  144  for each of the twenty-four disc surfaces of the twelve discs  104 . The twenty-four load arms  146  are mounted to thirteen actuator arms of the E-block for rotation about axis  148  under the influence of voice coil motor  140 . A pair of stop arms  150  and  152  are formed from the yoke of motor  140  to react against stop pins  154  and  156  mounted to housing  102  to define the limit of rotational travel of E-block  142 , thereby defining the inner and outer tracks on discs  104 . The engagement of stop arm  150  to stop pin  154  defines an inner stop position that limits the inner rotational travel of E-block  142  about the axis  148 , thereby defining the inner track of the discs. The engagement of stop arm  152  to stop pin  156  defines an outer stop position that limits the outer rotational travel of E-block  142  about the axis  148 , thereby defining the outer track of the discs. 
     As in the prior art 3½ inch disc drive, the inner track radius of the disc drive shown in  FIGS. 3 and 4  is 20.4 mm, but the outer track radius is 40.2 mm (1.583 inches) from spindle axis  108  of discs  104 , rather than 45.7 mm as in the prior art. Conveniently, a latch mechanism  160  is mounted to housing  102  to engage stop pin  362  on arm  152  when the actuator assembly is in a rest or shipping position at an inner track of discs  104 . Latch mechanism  160  is illustrated particularly in FIG.  3  and in detail in  FIG. 11 , and includes a housing  350  formed of rigid plastic mounted to a pin or bearing  352  mounted to the disc drive housing and arranged to pivot about the axis of pin  352  in the direction of arrows  354 . Housing  350  includes a first arm  356  having a detent  358  and lip  360  arranged to engage pin  362  on stop arm  152 . Housing also includes a second arm  364  having a small permanent magnet  366  having north and south poles  367 ′ and  367 ″. Pins  368  and  370  are constructed of magnetic metal, such as magnetic stainless steel, and are rigidly mounted to the disc drive housing to define a limit to the rotation of housing  350  about the axis of pin  352  and to hold housing  350  at one of its limit positions by magnetic force of magnet  366 . When voice coil  140  operates to move E-block  142  to an innermost track position, pin  362  engages lip  360  to rotate latch housing to the position illustrated in  FIGS. 3 and 11  to retain pin  362  mounted to stop arm  152  in detent  358 . Magnet  366  engages pin  368  to prevent rotation of housing  350  due to physical shock. Hence, during transportation of the disc drive, magnet  366  and pin  368  retain the position of housing  350  to prevent rotation of E-block  142 . To disengage pin  362  from detent  358 , current applied to voice coil motor  140  provides sufficient force so that pin  362  reacts against detent  358  to rotate housing  350  about its axis, so that magnet  366  is attracted to pin  370  to move housing  350  to its unlatch position, opposite that shown in  FIGS. 3 and 11 . 
     The latch mechanism  56  of the prior 3½ inch disc drive shown in  FIG. 1  was placed beside the actuator arm, near the space occupied by flex cable  42  for bending as the actuator arm rotated between its limit positions. The smaller disc diameter of the present invention, coupled with the shorter length of the actuator arm, permits the axis  148  of E-block  142  to be placed closer to axis  108  of the disc spindle than in prior disc drives. As a result, latch mechanism  160  may be placed behind voice coil  140  from E-block  142  ( FIG. 4 ) without sacrificing the active length of the voice coil, thereby gaining improved access to the actuator assembly for connection of flex cable  172  to the actuator. Moreover, space within the drive is available to add future improvements in the actuator assembly thereby improving the disc drive. 
     The disc drive illustrated in  FIGS. 3 and 4  has a track density of 9000 tracks per radial inch (354.3 tracks per radial mm) of each disc. With twelve discs as described, the disc drive illustrated in  FIGS. 3 and 4  has a data capacity of about 18 gigabytes. 
     Baffles  176  and  178  are employed about the outer periphery of the discs to channel air movement and reduce drag on the discs. An aperture  380  ( FIGS. 7 and 8 ) is provided in a wall of housing  102  to permit the clock write head to access the servo track of the disc drive, and bottom aperture  382  ( FIGS. 7 and 8 ) provides a seat for disc spindle  106  and its associated bearings; aperture  382  being sealed by a gasket and insertion of the disc spindle to the housing. 
     A stainless steel cover  182  ( FIGS. 4 and 6 ) is fastened to the top surface of housing  102  with a gasket  184  to seal the chamber of the housing and protect the disc drive from contaminants that might otherwise enter the drive. The top cover is fastened to housing  102  by threaded fasteners (not shown). A bottom cover  192  ( FIG. 7 ) is fastened to the bottom wall of housing  102  to close a desiccant chamber. Bottom cover  192  comprises a metal plate assembled into the opening  194  in the bottom wall and held in place and sealed by adhesive tape  198 . With the covers in place, the overall height of the disc drive is 41.15 mm (1.62 inches). 
     In the prior art, the desiccant member  68  ( FIG. 1 ) was positioned in housing  10  between bulkhead connector  40  and the inside surface of side wall  22 . It was necessary to insert the desiccant package  68  prior to sealing the drive. The desiccant package was then exposed to the relatively humid ambient conditions for a considerable amount of time during servo track writing and other testing before ling the drive. The present invention employs a desiccant housing  186  that permits placement of desiccant  188  into the housing immediately before closing and sealing the disc drive, so the desiccant is exposed to humid air outside the drive for a minimal period of time. 
       FIG. 7  is an exploded bottom view of the disc drive housing  102  and bottom cover  192 , and  FIG. 8  is a section view of the housing  102  (without covers) taken at line  8 — 8  in FIG.  3 . As shown in  FIG. 7 , a desiccant housing  186  is integral with the bottom wall of housing  102 . Desiccant housing  186  has side walls that define a length and width to a desiccant chamber containing desiccant pack  188 . One of the width side walls of desiccant housing  186  is common to one of the width side walls of disc drive housing  102  so that the desiccant housing is oriented lengthwise within the disc drive housing with the walls defining the length of the desiccant housing being substantially parallel to the walls defining the length of housing  102 . Desiccant housing  186 , being integral with the bottom wall of housing  102 , forms a structural beam for the bottom wall of housing  102  to provide additional structural strength for the housing. Desiccant housing  186  forms an opening  194  in the bottom wall of housing  102  and is closed and sealed by bottom cover  192 , assembled into opening  194  and held in place and sealed with flexible adhesive tape. Desiccant pack  188  is inserted into the housing  186  immediately prior to fastening the bottom cover  192  to the housing to maintain the humidity within the disc drive to a design level. As shown in  FIG. 8 , the top edge  196  of desiccant housing  186  is in a plane that is sloped from the common wall with housing  102  and downwardly toward the bottom wall or deck of housing  102  to form a sloped opening between the desiccant chamber within housing  186  and the disc drive components in the chamber enclosed within housing  102  and the top and bottom covers. The sloped opening permits good air circulation between the disc drive chamber and the desiccant in housing  186  to maintain the humidity within the disc drive chamber at a design level. Conveniently, the angle of the plane of sloped opening  196  is between about 20° and 25° from the plane of the bottom surface. 
     During assembly, the components of the disc drive are assembled by access into the disc drive chamber through the top opening of housing  102 . Upon completion of the assembly, the top cover is attached and sealed to disc drive housing  102 . Desiccant pack  188  is then placed within housing  186  which is then closed and sealed with bottom cover  192  and flexible tape, as described above. Since the desiccant is exposed to the atmosphere for a minimal period of time during final assembly, damage to the desiccant due to atmospheric conditions is minimized. As a result, the desiccant is able to immediately adjust the enclosed atmosphere of the disc drive chamber to the design humidity. 
     As described above, the bottom wall of housing is thinner than in the prior art drive. The thinner housing walls are adequate because of the smaller opening required for the discs. Moreover, the orientation of desiccant housing  186  along the long dimension of housing  102  more centrally from the side walls permits the desiccant housing to form a strengthening member for the housing. The orientation of desiccant housing  186  longitudinally within the disc drive housing provides structural support for the disc drive housing and overcomes any structural loss due to the thinner housing walls. The 20° and 25° angle to the slope of the top of desiccant housing  186  does not detract from the strengthening effect to housing  102  provided by the desiccant housing. 
     Lip  115  provides a minimum of 7.6 mm on which to seat gasket  184  to seal the disc drive with cover  182 . The prior art drive provided a seat dimension of 2.5 mm at the minimum location, which often resulted in the gasket mis-seating against the housing and cover so that the drive was not properly sealed and contaminants could enter the drive. 
     The footprint of the drive is 101.6 mm by 146 mm, as in the prior art. However, only about 91.4 mm (3.6 inches) of the width of the drive is required for the drive components. As shown in  FIGS. 5 and 6 , the 10.2 mm (0.4 inches) savings permits the addition of heat fins  190 , extending as much as 5.1 mm (0.2 inches) into the space surrounding the disc cavity to increase the surface area of housing  102  to further dissipate heat from the drive. 
     A “low-profile” version of the disc drive illustrated in  FIGS. 3 and 4  comprises a disc drive with six discs (instead of twelve in a half-high drive) so that the stack height is 13.56 mm (0.534 inches), instead of 11.37 mm stick height of low-profile drives of the prior art and 28.88 mm stack height of half-high drives according to the present invention. The overall or profile height of the low-profile disc drive of the present invention, with the cover in place, is 25.4 mm (1.00 inches), instead of 41.15 mm in a half-high drive, and is the same as in the prior art low-profile drive of  FIGS. 1 and 2 . As in the prior art, the low-profile and half-high versions of the drives according to the present invention enjoy the same foot print, size and style of recording discs and essentially the same actuator arm seek times. However, because there are half as many discs in a low-profile drive, the total data capacity is also half that of a half-high drive. Hence, the low-profile drive has a capacity of about 9 gigabytes, compared to 18 gigabytes of the half-high drive. 
     The actuator assembly comprising E-block  142 , load arm  146 , head/slider  144 , voice coil  140  and stop arms  150  and  152  are smaller than the corresponding actuator assembly of the prior art. More particularly, the actuator assembly shown in  FIG. 3  has a length of 45.7 mm (1.8 inches) from axis of  148  to the transducing gap of head  144  and has a shorter overall stroke between the inner and outer tracks. Consequently, the average stroke of the actuator assembly is smaller than in the prior drive. As a result, the actuator arm requires a smaller inertia of 67.7 gram-cm 2  (10.5 gram-inch 2 ), and track seeks of the drive illustrated in  FIGS. 3 and 4  require an average of 5.7 msec, 2 msec faster than the prior art drive illustrated in  FIGS. 1 and 2 . 
     Non-repeatable runout is the condition of unpredictable movement between the head and the disc causing tracking errors. The movement may be caused by a variety of factors, including bearing vibration, actuator vibration and wind turbulence. It is known, for example, that windage between the discs causes turbulence and air pressure variations from the inner radius to the outer radius. Pressure variations between the discs causes the discs to “flutter”, adversely affecting track positioning and adversely affecting non-repeatable runout. By reducing the diameter of the discs over the standard discs previously employed, and by reducing the spacing between the discs over the disc spacing previously employed, windage and pressure variations are reduced, resulting in thereby improving the non-repeatable runout characteristics of the disc drive of the present invention over those of the prior art. Table I illustrates the improved non-repeatable runout achieved by a 3½ inch disc drive (84 mm disc) of the present invention over 3½ inch disc drives (95 mm disc) of the prior art, both operating at the same rotational velocity. 
     
       
         
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                   
                 Runout at 
                 Runout at 
                 Runout at 
               
               
                 Disc (dia) 
                 20.4 mm 
                 40.2 mm 
                 45.7 mm 
               
               
                   
               
             
             
               
                 95 mm (3-Σ) 
                 0.245 microns 
                 0.309 microns 
                 0.335 microns 
               
               
                 84 mm (3-Σ) 
                 0.193 microns 
                 0.206 microns 
               
               
                 95 mm (w/c) 
                 0.361 microns 
                 0.502 microns 
                 0.554 microns 
               
               
                 84 mm (w/c) 
                 0.283 microns 
                 0.335 microns 
               
               
                   
               
             
          
         
       
     
     Table I compares the runout of  3½ inch disc drives having standard  95 mm discs to 3½ inch disc drives according to the present invention having an 84 mm disc. Illustrated are the measured runout at the inner data track (20.4 mm), at 40.2 mm inch radius (which is the outer data track for the 84 mm discs) and at 45.7 mm radius (which is the outer data track for the 95 mm discs). One set of data is runout data for the disc drives in accordance with the 3-sigma (3-Σ) standard deviation, and the other set of data reflects the worst case (w/c) runout for the disc drives. It will be appreciated that the disc drive according to the present invention exhibits non-repeatable runout that is between 0.052 and 0.078 microns improvement over the prior art drives at the inner data track and between 0.103 and 0.167 microns improvement at the 40.2 mm inch radial position (which is the outer data track of the 84 mm discs, but somewhat inboard of the outer data track on the 95 mm discs). This represents non-repeatable runout performance improvements of between 21% and 33%. 
     As shown in  FIG. 3 , stop arms  150  and  152  engage a stop pin  154  or  156  to define the stop positions that limit of rotational travel of E-block  142 . As shown particularly in  FIGS. 12 and 14 , stop arms  150  and  152  have flat surfaces  151  and  153 , respectively to engage stop pins  154  or  156 . One feature of the invention resides in the ability to accurately locate and position the inner and outer tracks of discs  104 . More particularly, E-block  142  is placed in a shuttle (not shown). The gimbal/slider head assembly  146 ,  144  is swagged to the E-block and the position of the transducing gap or element of head  144  is located with respect to the shuttle and to axis  148  of the actuator assembly. The distance between axis  148  and transducer is represented by distance  250 . The distance between the innermost and outermost data tracks being known (e.g., 19.8 mm in the present invention), the total angular displacement of the E-block can be geometrically identified. Likewise, the distance  252  between axis  148  and the arc  254  of movement of stop surfaces  151  and  153  is also known from the geometry of the E-block. Consequently, the positions of surfaces  151  and  153  may be milled or otherwise adjusted to accurately position the angular travel of head  144  in the full extent of movement of the E-block. The milling of surfaces  151  and  153  is performed in planes that project through axis  148  so that surfaces  151  and  153  are normal to the arc of travel of the yoke arm as the E-block rotates about the axis. Therefore, upon completion of the assembly of the E-block into the disc drive, the position of the inner and outer tracks is accurately determined. 
     One feature of the stop assembly resides in the fact that the stop surfaces are on the yoke arms of the motor assembly for the E-block, distal from the spindle axis and arranged to engage a stop pin  154 ,  156  mounted to the disc drive housing. In the prior art drive, stop pin on the E-block was mounted to an extension arm adjacent the flex circuit and near the spindle axis to engage a surface of the housing. Because of the proximity of the stop arrangement to the E-block, any error in positioning the stop surfaces was magnified along the greater distance (for example,  250 ) of the actuator arm to the head. More particularly, the distance between the spindle axis and transducer was typically three times the distance between the spindle axis and the stop surface, so any error in positioning the stop surface was magnified up to three times to the head. By positioning the stop surface at the distal end of the yoke as in the present invention, coupled with the shorter actuator arm of the E-block due to the smaller recording discs, the distance between the head  144  and the spindle axis  148  is nearly the same as the distance between axis  148  and stop surfaces  151  and  153 . As a result, any error in the positioning of stop surfaces  151  and  153  is not magnified to the head as in the prior art. 
     One feature of the disc drive of the present invention resides in the access to flex circuit  172  and E-block  142  to permit connection of the flex circuit to conductors supported by the E-block for the heads. This feature is particularly illustrated in  FIGS. 12-15 . 
       FIG. 12  illustrates a portion of the actuator assembly of the present invention. The actuator assembly includes E-block  142  having a plurality of actuator arms  204 ′ . . .  204 ″″. For the twelve discs of the disc drive illustrated in  FIGS. 3 and 4 , there are thirteen actuator arms  204  of E-block  142 . Actuator arms  204 ′ and  204 ″″ carry a single load arm  146  and head  144  (FIG.  3 ), whereas actuator arms  204 ″ . . .  204 ′″ each carry two load arms  146  and heads  144 . Each disc spins between two actuator arms, load arms and gimbal/slider/head arrangements so that a single head confronts each disc surface. As shown in  FIG. 12 , actuator E-block  142  includes a plurality of thirteen slots  210  extending between an axial slot  212  and actuator arms  204 . 
       FIG. 13  illustrates a plurality of load arms  146  terminating at heads  144  on sliders. A ribbon of conductors  214  extends from heads  144  and terminates at tabs  216 . The ribbon  214  comprises a suitable insulator material, such as Kapton encapsulating printed copper traces that provide electrical connection between tabs  216  and heads  144 . For flexibility, ribbon  214  is preferably about 2 to 3 mils thick. Tabs  216  on each ribbon form conductive terminations for the copper traces on the ribbon. Tabs  216  project outwardly from ribbon  214  opposite a fin  218 . Each fin  218  is constructed of Kapton and copper traces, and has a thickness that may be equal to the thickness of ribbon  214 . Ribbons  214  further include terminations  228  that distribute electrical connections from the ribbon portion to heads  144 . Each termination  228  is adhesively attached to one side of a respective load arm  146  on a side of the load arm opposite head/slider  144 . With load arms  146  mounted to actuator arms  204  and terminations  228  attached to the load arms, ribbons  214  extend along the length of the actuator arms along one side thereof. Ribbons  214  and fins  218  are located in slots  210  in E-block  142  (FIG.  12 ). In the case of actuator arms  204 ′ and  204 ″″, slot  210  is wide enough to accommodate a single ribbon and fin assembly, whereas the slots for actuator arms  204 ″- 204 ′″ are wide enough to accommodate two ribbon and fin assemblies for the two head supported by the arm. 
     Substrate  220  ( FIG. 13 ) is mounted to E-block  142  and includes a plurality of extensions  222  forming slots  224  therebetween, matching slots  210  on E-block  142  at the position of tabs  216 , except there is no slot  224  corresponding to a the uppermost and lowermost slots  210  on the E-block. Each extension  222  includes a plurality of conductive pads  226  extending to and facing an individual slot  224 . Each pad  226  corresponds to an individual one of tabs  216  of ribbons  214 . With the ribbons  214  in place and fins  218  assembled into slots  210 , the individual tabs  216  protrude through slots  224  in substrate  220  adjacent each pad  226 . Tabs  216  are thereupon bent into contact with an individual pad  226  and soldered in place, such as by reflow soldering. 
     As shown particularly in  FIGS. 14 and 15 , flexible circuit  172  provides a flexible connection to substrate  220  and is mounted thereto and sandwiched against E-block  142  by fasteners  232 . As shown particularly in  FIG. 15 , stiffener plate  234  sandwiches the assembly together to rigidly connect flex circuit  172  to substrate  220  and to the E-block. Stiffener plate  234  provides a rigid mount of substrate  220  to the E-block and substrate  220  fixedly positions ribbons  214  and their respective fins in the respective slots in the E-block. Because fins  218  extend into the E-block and are held in their respective slots  210  by the rigid fastening of tabs  216  to substrate  220  which is rigidly positioned by stiffener plate  234 , fins  218  cannot accidently separate from slots  210 . Consequently, fins  218  may be loosely received in the slots, and held in place by stiffener plate  234 . 
     The connector assembly of the present invention may be largely assembled outside the disc drive. More particularly, heads and suspensions are assembled to load arms  146  which are swagged to the actuator arms of the E-block. Ribbons  214  are connected to the heads and assembled into the slots  210  in load arms  146  and the E-block. Substrate  220  is assembled to the E-block. Due to the nesting of fins  218  to respective slots  210 , ribbons  214  are properly aligned so that the protruding tabs  216  are in alignment with pads  226  on substrate  220 . With the alignment completed, tabs  216  are soldered to pads  226  to complete the assembly of the ribbons to the E-block. Flex circuit  172  is then connected to substrate  220  and stiffener plate  234  is mounted to the E-block. Final assembly is accomplished by assembling actuator assembly into the drive housing and connecting flex circuit  172  to bulkhead connector  170  (FIG.  1 ). 
     During assembly, ribbons  214  are held in place in slots  210  in the E-block by virtue of fins  218  extending more deeply into the slots  210  in the E-block directly opposite the connection of tabs  216  to the substrate. With the opposite ends of ribbons  214  being connected to the load arms by the adhesive attachment of terminations  228 , a small tension is imposed on ribbons  214  to hold them in place in the slots for alignment of tabs  216  to pads  226  during soldering. This arrangement ensures that fins  218  remain in slots  210 , thereby ensuring that ribbons  214  remain in place during assembly, even though the ribbons and fins are loosely coupled to the slots  210 . The solder connection of tabs  216  to pads  226  assures rigid mounting of ribbons  214  to substrate  220  (which in turn is rigidly mounted to the E-block). Moreover, although slots  224  in substrate  220  provide convenient access of the tabs to the exposed surface of the substrate, slots  224  are not necessary for the placement of fins  218  in slots  210 , and the fins remain in their respective slots  210  even if slot  224  is not present. Most particularly, as shown in  FIG. 3 , the tabs  216  of the uppermost and lowermost ribbons do not extend through slots  224  in substrate  220 . Instead, these ribbons, like the other ribbons of the assembly, are held in place by fins  218  in slots respective  210 . 
     The present invention thus provides an improved disc drive utilizing a smaller-than-standard disc diameter in a standard disc drive housing configuration without sacrificing overall data capacity. The smaller discs require less power for a given rotational velocity, resulting in the ability to achieve higher spindle speeds and reduce latency without increasing spindle power consumption over that of prior larger, slower drives. Additionally the disc drive exhibits a significant reduction in seek time without increasing data densities. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.