Magnetic disk apparatus with circuit capable of identifying individual specification

A magnetic disk apparatus is disclosed, in which the product specifications such as the number of heads, the number of disks and the information on the destination of the apparatus can be efficiently, accurately identified by a single circuit. The magnetic disk apparatus comprises an identification circuit that can identify the performance specification information. The identification circuit includes a first resistor circuit arranged on a cable connecting a head actuator and a printed board, a second resistor circuit formed on the printed board and having an end thereof connected to a reference voltage and the other end thereof connected in series to the first resistor circuit, an A/D converter for converting the voltage value at the junction point of the first and second resistor circuits into a digital value of a predetermined number of bits, and a memory for storing in advance the performance specification information and the control information of the magnetic disk apparatus corresponding to a digital value of a predetermined number of bits. The control circuit on the printed board can thus control the magnetic disk apparatus by judging the performance specification information of the magnetic disk apparatus from the output value of the A/D converter and the value stored in the memory.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a magnetic disk apparatus which is a 
memory apparatus or, in particular, to a magnetic disk apparatus 
comprising a performance specification identification circuit capable of 
identifying the individual performance specification of the magnetic disk 
apparatus with a simple configuration. 
2. Description of the Related Art 
In recent years, the performance of a magnetic disk apparatus has come to 
depend to a large measure on the characteristics of the heads or the 
magnetic disks providing a storage medium. For this reason, it is 
necessary to strictly manage the characteristics of the heads and the 
disks, and the magnetic disks must be used under conditions conforming to 
the respective characteristics. 
The characteristics of the heads and magnetic disks have conventionally 
been managed mainly on the assembly line for the disk apparatus. 
Specifically, a worker makes it a practice to visually check the number of 
the magnetic disks and the number of the heads or the type of the control 
IC of the magnetic disk apparatus in the process of assembly, and attaches 
a label or the like conforming to the configuration of the magnetic disk 
apparatus on the reverse side of the housing to thereby identify the type 
of the magnetic disk apparatus. 
The latest trend, however, is toward an increased number of types of heads 
and magnetic disks, of the magnetic disk apparatus, which are supplied 
from a plurality of suppliers. Further, in order to increase the range of 
articles by changing the storage capacity of the magnetic disk 
apparatuses, different numbers of heads or magnetic disks are sometimes 
mounted in the same housing. The characteristics of the heads and the 
magnetic disks may thus vary from one supplier to another. In the case 
where the heads and the magnetic disks are purchased from different 
suppliers, therefore, the characteristics corresponding to the respective 
parts are preferably recognized by the control circuit of each magnetic 
disk apparatus to control the apparatus with a control constant most 
suitable to each part. 
With the increased number of combinations of the number and type of the 
heads and the magnetic disks and the number of the types of the control IC 
for the control circuit delivered from different suppliers, it has become 
increasingly difficult to set up or manage individual magnetic disk 
apparatuses conforming to the respective component elements thereof. 
Another current trend is toward an increased use of a composite head 
including a MR (magnetoresistive) head and an inductive head for the 
magnetic disk apparatus. The resultant problem is a change in the 
characteristics of the magnetic disk at low temperatures (deterioration of 
the overwrite (O/W) characteristic) that adversely affects the data 
read-write characteristics, and a solution to this problem is desired. 
In a magnetic disk apparatus, the signal reproduced by the head is passed 
out of the housing through a flexible circuit board mounted on the side of 
the carriage, and led to a printed circuit board arranged on the reverse 
side of the housing. The head IC and the servo IC for demodulating the 
read signal supplied by the head are often mounted on the flexible circuit 
board (hereinafter referred to as the flexible cable). 
In the magnetic disk apparatus, the number of the magnetic disks 
accommodated in the same housing are sometimes changed by a modification 
to the specification by the supplier of the magnetic disk apparatus. In 
the case where the head IC for processing the signals from the head or 
circuit components such as the capacitors and resistors forming the 
peripheral circuit are mounted on the flexible cable, a separate circuit 
for identifying the specification information of the magnetic disk 
apparatus is mounted on each of the flexible cable and the printed circuit 
board. 
The identification circuit for the specification information of the 
magnetic disk apparatus generally includes a pull-down circuit having a 
resistor mounted on the flexible cable and a MCU (microcomputer unit) as a 
control IC for the magnetic disk apparatus mounted on the printed circuit 
board 79. 
This specification information identification circuit for the magnetic disk 
apparatus can represent two states according to the presence or absence of 
the resistor in the pull-down circuit. In the case where a magnetic disk 
apparatus having the same housing specification has two specifications for 
the magnetic disk, one involving a single magnetic disk, and the other 
involving two magnetic disks, for example, the two states are 
distinguished by changing the resistance value of the resistor. 
In this method, however, only two states can be represented by each 
pull-down circuit. If the type and the number of the heads is to be 
identified in addition to the number of magnetic disks, therefore, an 
increased number of the pull-down circuits are required, thereby posing 
the problem of an increased number of connectors, MCU pins and resistors 
leading to an increased overall cost. 
Further, for the specification information to be obtained on the number of 
each type of magnetic disks and the type and the number of the heads of 
each magnetic disk in the process of fabrication of a magnetic disk 
apparatus, such information must be read from the label attached to the 
individual magnetic disk apparatuses. In the conventional method, the bar 
code printed on the label is read by a tester, so that a program code and 
read/write parameters suited to each housing of the magnetic disk 
apparatus are downloaded. 
With regard to the deterioration of the overwrite characteristic at low 
temperatures which has recently posed a problem, on the other hand, it is 
known that the read/write characteristic can be improved by increasing the 
write current. An excessively increased write current, however, is liable 
to destroy the data in adjacent tracks by write expansion. 
A means for solving these problems is disclosed in JP-A-64-79904, 
JP-A-1-137409 and JP-A-1-166361, in which a resistor is mounted on both 
the flexible cable in the magnetic disk apparatus and on the printed 
circuit board (hereinafter referred to simply as the printed board) 
outside the magnetic disk apparatus. The two resistors are connected in 
series, so that a reference voltage is applied to them and the partial 
voltage appearing at the junction point is identified by a voltage 
comparator. 
The method described in the above-mentioned patent publications, however, 
requires a series-connected resistor and a comparator for detecting a 
partial voltage at the junction point thereof for each identification item 
of the magnetic disk apparatus. For identifying a multiplicity of items, 
therefore, a correspondingly increased number of voltage comparators are 
required, giving rise to a new problem of an increased size and hence an 
increased cost. 
Another problem of the method described in the above-mentioned patent 
publications is that the internal temperature of the housing of the 
magnetic disk apparatus cannot be detected and therefore the deterioration 
in the overwrite characteristic at low temperatures cannot be prevented. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a magnetic 
disk apparatus in which the type and the number of heads and magnetic 
disks and many states such as customized information can be efficiently 
and positively identified by a single circuit. 
Another object of the invention is to provide a magnetic disk apparatus in 
which the read/write characteristic at low temperatures can be improved 
using the above-mentioned circuits while avoiding write expansion to 
adjacent magnetic tracks. 
According to one aspect of the invention, there is provided a magnetic disk 
apparatus comprising resistor circuits on both a printed board and a 
circuit from the cable to the head actuator, which resistor circuits are 
connected in series and supplied with a reference voltage. A partial 
voltage appearing at the junction point of the resistor circuits is A/D 
converted, and the magnetic disk information is identified, by a control 
circuit, from the digital value thus obtained. 
If the magnetic disk information identified by the control circuit can be 
recognized by a tester in the process of fabrication, an appropriate 
program code and a read/write parameter can be written without reading the 
label on the one hand, and detailed data can supplied for quality control 
of the magnetic disk apparatus at the same time. 
According to a second aspect of the invention, there is provided a magnetic 
disk apparatus in which the internal temperature of the housing of the 
magnetic disk apparatus is detected, and the write current to the head is 
controlled by the control circuit on the basis of the detected 
temperature. Specifically, while avoiding write expansion, the read/write 
characteristic at low temperatures is improved by increasing the write 
current to the head when the internal temperature of the housing is low, 
and by decreasing the write current when the internal temperature is high.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Before describing the preferred embodiments, an explanation will be given 
of the conventional magnetic disk drive shown in FIGS. 1 to 4. 
FIG. 1A shows an example of a structure of a conventional magnetic disk 
apparatus 70. In FIG. 1A, reference numeral 71 designates a base, numeral 
72 a plurality of magnetic disks, numeral 73 a spindle motor for rotating 
the disks 72, numeral 74 an actuator including a carriage 75 having heads 
76 at the forward end thereof and a voice coil motor 77, numeral 79 a 
printed board for mounting a control circuit of the magnetic disk 
apparatus 70, and numeral 80 a cover. 
With this magnetic disk apparatus 70, the signals reproduced by the heads 
76 are passed out of the base 71 on a flexible circuit board, not shown, 
mounted on the side of the carriage 75, and introduced onto the printed 
board 79 arranged on the reverse side of the base 71. A head IC and a 
servo IC for demodulating the read signals supplied by the heads 76 are 
mounted in many cases on the flexible circuit board (hereinafter referred 
to as the flexible cable). 
FIG. 1B shows a configuration of the magnetic disk apparatus 70 of FIG. 1A 
in which the number of the magnetic disks 72 is reduced by one. In FIG. 
1B, the same component members as in FIG. 1A are designated by the same 
reference numerals, respectively. In this way, the number of the magnetic 
disks 72 in the same base 72 is sometimes changed depending on the 
specification of the supplier of the magnetic disk apparatus 70. 
FIG. 2 shows another example configuration of a conventional magnetic disk 
apparatus 90. The same component members in this magnetic disk apparatus 
as those included in the magnetic disk apparatuses shown in FIGS. 1A, 1B 
are designated by the same reference numerals, respectively. Thus, numeral 
71 designates a base, numeral 72 a plurality of magnetic disks, numeral 73 
a spindle motor, numeral 74 an actuator including a carriage 75 with a 
head 76 at the forward end thereof and a voice coil motor 77, numeral 78 a 
flexible cable, and numeral 79 a printed board arranged on the reverse 
side of the base 71. 
The flexible cable 78 used with this magnetic disk apparatus 90, as shown 
in FIG. 3, includes a movable portion (carriage-mount) 78A mounted on the 
side of the carriage 75, a curved portion 78B connected to the movable 
portion 78A, a fixed portion (base portion) 78C connected at right angles 
to the end of the curved portion 78B, and a connector 78D formed at the 
tip of an extended forward end of the fixed portion 78C. The area of the 
fixed portion 78C is so large that a head IC 91 for processing the signals 
from the heads and circuit components 92 such as capacitors and resistors 
constituting the peripheral circuit of the head IC 91 are mounted on the 
fixed area 78C. A small signal from each head is applied through a circuit 
pattern formed of the movable portion 78A, the curved portion 78B and the 
fixed portion 78C and amplified by the head IC 91 mounted on the fixed 
part 78C. 
The flexible cable 78, configured in this way, as shown in FIG. 2, has the 
fixed portion 78A thereof mounted on the side of the carriage 75, the 
curved portion 78B thereof is folded back and led out of the carriage 75, 
and the fixed portion 78C thereof is fixed on the base 71 by being bent by 
90.degree. with respect to the curved portion 78B. At the same time, the 
connector 78D is protruded out of the base 71, and the protrusion is bent 
toward the reverse side of the base 71 and connected to a connector not 
shown mounted on the printed board 79 through a recess 71A formed in the 
base 71. 
As described above, a head IC for handling the signals from the heads 76 is 
arranged on the flexible cable 78 of the conventional magnetic disk 
apparatuses 70, 90. The circuit for identifying the specification 
information of the magnetic disk apparatuses 70, 90 is arranged in two 
parts, one on the flexible cable 78 and the other on the printed board 79. 
FIG. 4 shows a configuration of a specification information identification 
circuit of a conventional magnetic disk apparatus. In the conventional 
magnetic disk apparatuses 70, 90, as shown in FIG. 4, a pull-down circuit 
60 including a resistor 61 is arranged on the flexible cable 78. This 
pull-down circuit 60 is connected to a MCU (microcomputer unit) 85 
constituting a control IC of the magnetic disk apparatus through a 
connector 82 arranged on the flexible cable 78 and the printed board 79. 
The resistor 61 connected to the ground of the pull-down circuit 60 has an 
end thereof connected to the ground in the printed board 79, and the other 
end of the resistor 61 is connected to a power supply Vcc through a 
pull-up resistor 86 in the MCU 85. 
The specification information identification circuit of the magnetic disk 
apparatus configured as described above can represent two states according 
the presence or absence of the resistor 61 in the pull-down circuit 60. 
Assume, for example, that the magnetic disk apparatus having the same 
housing specification has two specifications, one magnetic disk and two 
magnetic disks. In the case where only one magnetic disk is included in 
the specification, a resistor (whose resistance is approximately 0.OMEGA.) 
is installed, while if the specification covers two magnetic disks, no 
resistor is installed. The voltage at the port terminal 87 of the MCU 85, 
therefore, is 0V when one magnetic disk is involved, and 5V when there are 
two magnetic disks. It can thus be determined that when the logic level is 
L (low level), one magnetic disk is used, while when the logic level is H 
(high level), two magnetic disks are used. 
This method can represent only two states for each pull-down circuit 60. If 
the type or the number of the heads is to be identified in addition to the 
number of magnetic disks, however, the number of the pull-down circuits 
must be increased accordingly, thereby leading to the problem of the 
requirement for an increased number of the connectors 82, the pins of the 
MCU 85 and the resistors 61 and a higher cost. 
Further, if the specification information such as the number of magnetic 
disks and the type and number of heads for each magnetic disk is to be 
obtained for each magnetic disk in the fabrication process of the magnetic 
disk apparatus, such information must be read from the label attached. In 
the prior art, the bar code printed on the label is read by a tester, so 
that a program code and a read/write parameter suitable for each housing 
of the magnetic disk apparatus is downloaded. 
With regard to the deterioration of the overwrite characteristic at low 
temperatures which has recently posed a problem, on the other hand, the 
read/write characteristics are known to be improved by increasing the 
write current. If the write current is increased excessively, however, the 
data in adjacent tracks may be destroyed by write expansion. 
A means for solving these problems is proposed, for example, in 
JP-A-64-79904, JP-A-1-137409 and JP-A-1-166361, in which a resistor is 
arranged on both the flexible cable in the magnetic disk apparatus and a 
printed circuit board (hereinafter referred to simply as the printed 
board) outside the magnetic disk apparatus, and these resistors are 
connected in series and supplied with a reference voltage thereby to 
identify the partial voltage appearing at the junction point by a voltage 
comparator. 
In the method described in the above-mentioned patent publications, 
however, series-connected resistors and a comparator for detecting the 
partial voltage at the junction point thereof are required for each item 
of identification of the magnetic disk apparatus. For identifying many 
items, therefore, an increased number of voltage comparators is required, 
resulting in the new problem of an increased circuit size and cost. 
Also, the method described in the above-mentioned patent publications 
cannot detect the internal temperature of the housing of the magnetic disk 
apparatus, and therefore another problem is that the deterioration of the 
overwrite characteristics at low temperatures cannot be prevented. 
Preferred embodiments of the present invention will be specifically 
described below with reference to the accompanying drawings. 
FIG. 5 shows a basic configuration of a magnetic disk apparatus according 
to the present invention. As shown in FIG. 5, according to the present 
invention, there is provided a magnetic disk apparatus comprising a 
housing, at least a magnetic disk 1, at least a head 2, an actuator 3 for 
moving the head 2, and a printed board 5 having mounted thereon a control 
circuit 4 arranged in the housing for processing the write signal to the 
head 2 or the read signal from the head, wherein the actuator 3 and the 
control circuit 4 are connected by a cable 6, the apparatus further 
comprising an identification circuit 10 capable of identifying the 
specification information of the magnetic disk apparatus. The 
specification information identification circuit 10 includes a first 
resistor circuit 11 of a predetermined resistance value mounted on the 
cable 6 or on the actuator 3 and having an end thereof grounded, a second 
resistor circuit 12 of a predetermined resistance value arranged on the 
printed board 5 with one end thereof connected to the reference voltage of 
the printed board and the other end thereof connected to the other end of 
the first resistor circuit through the cable, an A/D converter 14 for 
converting the voltage value appearing at the junction point 13 between 
the first resistor circuit 11 and the second resistor circuit 13 into a 
digital value having a predetermined number of bits corresponding to the 
magnitude of the voltage value and outputting the digital value, and a 
memory 15 having stored therein the specification information of the 
magnetic disk apparatus corresponding to the digital value having a 
predetermined number of bits output from the A/D converter 14 and the 
control information corresponding to the particular specification 
information, wherein the control circuit 4 connected to the A/D converter 
14 and the memory 15 judges the specification information of the magnetic 
disk apparatus from the output value of the A/D converter 14 and the value 
stored in the memory 15, so that the magnetic disk apparatus is controlled 
by the control information corresponding to the specification information 
stored in the memory 15. 
In this configuration, according to the first aspect of the invention, the 
voltage value at the junction point corresponding to all the specification 
information of the magnetic disk apparatus, a combination of the first 
resistor circuit 11 and the second resistor circuit 12 for producing the 
particular voltage value are predetermined, and the first resistor circuit 
11 and the second resistor circuit 12 are mounted at the time of 
fabricating the magnetic disk apparatus according to the specification of 
the magnetic disk apparatus. 
The first resistor circuit 11 and the second resistor circuit 12 can each 
be configured of a single resistor or a combination of a plurality of 
resistors. Further, the resistance value of one of the resistor circuits 
can be fixed while the resistance value of the other resistor circuit can 
be made variable thereby to determine the voltage value at the junction 
point. 
The apparatus is also so configured that in the case where the disk and 
head characteristics are stored in a memory for each disk and head, the 
control unit is configured to disregard the bit information for storing 
the characteristics of an absent disk or head. 
Furthermore, the specification information of the magnetic disk apparatus 
constitutes at least one of the pieces of information including the number 
of the magnetic disks 1, the number of the heads 2, the type of the disk, 
the head characteristics, information on the head control circuit and 
information on the user of the apparatus. The number of bits corresponding 
to the number of the pieces of the specification information thus 
identified is contained in the digital signal output from the A/D 
converter 14. 
In addition, the apparatus according to the second aspect of the invention 
having the above-mentioned configuration comprises a temperature sensor 16 
having a high internal impedance connected in parallel to the first 
resistor circuit 11, a change-over switch 17 inserted between the junction 
point of the first and second resistor circuits 11, 12 and the second 
resistor circuit 12, and a memory 15 having stored therein the temperature 
information corresponding to the digital value of a predetermined number 
of bits output from the A/D converter 14, wherein when the change-over 
switch 17 is closed, the control circuit 4 judges the specification 
information of the magnetic disk apparatus from the output value of the 
A/D converter 14 and the value stored in the memory 15, while when the 
change-over switch 17 is open, on the other hand, the output of the A/D 
converter 14 is monitored to detect the internal temperature of the 
housing at regular intervals of time. In this second aspect of the 
invention, the write current to the magnetic disk 1 is set from time to 
time by the control circuit 4 based on the internal temperature of the 
housing detected. 
FIG. 6 is a block diagram showing a circuit configuration of an 
identification circuit of a magnetic disk apparatus according to an 
embodiment of the present invention. 
In FIG. 6, numeral 6 designates a flexible cable for connecting the 
actuator 3 and the printed board 5 described with reference to FIG. 5. The 
flexible cable 6 has arranged thereon, as in the conventional magnetic 
disk apparatus 90 described with reference to FIGS. 2 and 3, a head IC 20 
for processing the signals produced from each head unit 2 including a 
plurality of heads 2A to 2N and circuit components (not shown) including 
capacitors and resistors making up the peripheral circuit of the head IC 
20. The head IC 20 contains therein a read/write circuit 21 and a 
switching circuit 22 for setting one of the heads 2A to 2N in a connected 
state. Although only the inductive head is shown in FIG. 6, the heads 2A 
to 2N each constitute a write-only head in the case of a composite head 
combined with the MR head. 
According to the present invention, the first resistor circuit 11 is 
arranged on the flexible cable 6. The first resistor circuit 11 includes a 
resistor Rd and a temperature sensor 16 in this embodiment. An end of the 
resistor Rd is grounded, and the other end thereof is connected to a print 
circuit 5 described later by the flexible cable 6. This temperature sensor 
16 is connected in parallel with the resistor Rd on the one hand and is 
connected to a power supply Vcc on the other hand. The temperature sensor 
16 has so high an internal impedance that when it is connected in parallel 
with the resistor Rd at room temperature, the value of the combined 
resistance of the temperature sensor 16 and the resistor Rd is 
substantially equal to the resistance value of the resistor Rd. 
The flexible cable 6 configured as described above is connected to the 
printed board 5 through a connector 7. 
The printed board 5 comprises therein a second resistor circuit 12 
connected to the first resistor circuit 11 on the flexible cable 6, an A/D 
converter 14 for A/D converting the voltage of the junction point 13 of 
the second resistor circuit 12 and the first resistor circuit 11, a 
control circuit (a microcomputer unit (hereinafter referred to as the MCU) 
in this case) 4 impressed with the digital signal output from the A/D 
converter 14, a read-only memory (hereinafter referred to as the ROM) 15 
for storing the specification information of the magnetic disk apparatus 
corresponding to the digital output of the A/D converter 14, a hard disk 
controller (HDC) 18 and a filter circuit 19. 
The second resistor circuit 12 includes a resistor Ru and a change-over 
switch 17 according to this embodiment. The resistor Ru has an end thereof 
connected to a reference power supply Vref, and the other end thereof 
connected to a junction point 13 with the resistor Rd on the flexible 
cable 6 through the change-over switch 17. The change-over switch 17 can 
be composed of a semiconductor switch such as a FET. As a result, a 
partial voltage value Vd of the reference voltage Vref obtained by voltage 
division based on the ratio between the resistance value of the first 
resistor circuit 11 and the resistance value of the second resistor 
circuit 12 appears at the junction point 13. A filter circuit 19 including 
a resistor and a capacitor is inserted between the junction point 13 and 
the ground. 
The A/D converter 14 is interposed between the reference voltage Vref and 
the ground, and has an input terminal thereof supplied with the voltage 
value at the junction point 13. The A/D converter 14 converts the analog 
voltage at the junction point 13 to a digital signal of a predetermined 
number of bits. The number of bits of the digital value output from the 
A/D converter 14 is determined in accordance with the number of 
specifications of the magnetic disk apparatus identified by the 
identification circuit 10. If the number of specifications of the magnetic 
disk apparatus is 16 (16 types), for example, the number of bits is 
determined as 4 (2.sup.4 =16) or more. 
The MCU 14 judges the specification of the magnetic disk apparatus in 
accordance with the digital signal applied thereto from the A/D converter 
14. This judgement is carried out by reference to the ROM 15 storing the 
specification according to the combinations of "0" and "1" of the digital 
signal. In accordance with the specification of this magnetic disk 
apparatus, the head IC 20 is controlled by the MCU 4. Also, the on/off 
operation of the change-over switch 17 is also controlled by the MCU 4. 
The output of the MCU 14 is produced through a HDC 18 and, according to 
this embodiment, is applied to a down-loader or a tester 30. 
In the above-mentioned embodiment, the resistance values of the first 
resistor circuit 11 and the second resistor circuit 12 were determined by 
a single resistor Rd, Ru, respectively. The number of resistors 
constituting the first resistor circuit 11 and the second resistor circuit 
12, however, is not limited to unity. Instead, a plurality of resistors 
can be connected in parallel or in series to determine a resistance value. 
FIG. 7A shows an embodiment in which the resistance value of the first 
resistor circuit 11 is determined as a combined resistance of resistors 
Rd1 and Rd2 connected in parallel, and the resistance of the second 
resistor circuit 12 determined by a combined resistance of resistors Ru1, 
Ru2. On the other hand, FIG. 7B shows an embodiment in which the 
resistance value of the first resistor circuit 11 is determined by a 
combined resistance of the resistors Rd1, Rd2 connected in series, and the 
resistance value of the second resistor circuit 12 is determined by a 
combined resistance of the resistors Ru1, Ru2 connected in series. 
According to the embodiments shown in FIGS. 7A, 7B, the first resistor 
circuit 11 includes no temperature sensor 17, and hence no change-over 
switch 17. 
FIG. 8 shows a table showing the partial voltage values at the junction 
point 13 of the first resistor circuit 11 and the second resistor circuit 
12, example combinations of the resistance values of the resistors Rd, Ru 
of the first resistor circuit 11 and the second resistor circuit 12 for 
realizing the partial voltage values, and example digital outputs of the 
A/D converter 14 corresponding to each partial voltage value in the 
magnetic disk apparatus according to the present invention described with 
reference to FIG. 2. In this example, the digital output signal of the A/D 
converter 14 is 5 bits. The identification circuit having the A/D 
converter 14 according to this embodiment, therefore, can identify 32 
different specifications of the magnetic disk apparatus. According to this 
embodiment, in order to identify 32 specifications of the magnetic disk 
apparatus, each partial voltage value assumes an integer multiple of 1/32 
of the reference voltage Vref. The partial voltage assumes a maximum value 
as a reference voltage Vref with the resistor Ru shorted. 
A voltage value to be converted into a given digital signal value in the 
A/D converter 14 is given some margin taking the error of the resistors 
Rd, Ru into consideration. Specifically, an arrangement is made to produce 
an output of the same digital signal value within a predetermined voltage 
range centered at the partial voltage value of FIG. 8. In the case where 
the partial voltage assume values in the order of 3V, 4V, 5V and so on, 
for example, the digital signal corresponding to the partial voltage value 
of 4V is adapted to be produced in the range of 3.5V to 4.5V not 
inclusive. 
FIG. 9 is a table showing an example of the identification information of 
the characteristics of the magnetic disk apparatus stored in the ROM 15 of 
FIG. 6 when the partial voltage values at the junction point 13 of the 
first resistor circuit 11 and the second resistor circuit 12 of the 
identification circuit 10 in FIG. 6 assumes the states shown in FIG. 8, 
respectively. This information is written beforehand in the ROM 15. In 
this example, the characteristics of the magnetic disk apparatus are 
judged using the first bit, the number of the magnetic disks are 
determined using the second bit, the characteristic of the head is judged 
using the third bit, and the number of heads is determined using the 
fourth and fifth bits of the digital signal output from the A/D converter 
14. 
Specifically, the R or S characteristic of the magnetic disk is judged 
depending on whether the first bit is 0 or 1, respectively; the number of 
the disks is determined to be 1 or 2 depending on whether the second bit 
is 0 or 1, respectively; the P or Q characteristic of the head is 
determined depending on whether the third bit is 0 or 1, respectively; and 
the number of heads is determined to be one of 1 to 4 depending on the 
combinations of 0 and 1 of the fourth and fifth bits. 
In the identification circuit 19 configured as described above, the 
change-over switch 17 is operated by the control signal produced from the 
MCU 4. When the change-over switch 17 is in closed state, the internal 
impedance of the output stage of the temperature sensor 16 is high and 
therefore a voltage corresponding to the ratio of resistance between the 
resistors Rd and Ru is generated at the junction point 13 of the first 
resistor circuit 11 and the second resistor circuit 12. The A/D converter 
14 converts the voltage value at the junction point 13 into a digital 
value. The MCU 4 refers to the data input thereto from the A/D converter 
14 and identifies the specification information of individual magnetic 
disks from the value of each bit in accordance with the information 
described with reference to FIG. 9. 
The individual specification information of the magnetic disks, once 
identified by the MCU 14, is transferred from the MCU 4 to the HDC 18. In 
this embodiment, the printed board 5 can be connected with the down-loader 
or tester 30. In the case where the down-loader 30 is connected, the 
information of the HDC 18 is read by the down-loader 30 through an 
interface, so that a proper program code or a read/write parameter is 
written on the magnetic disk. In the case where the tester 30 is 
connected, on the other hand, the information, after being read by the 
tester 30, can be collectively managed and used for production control 
such as for calculating the ratio of conforming articles. 
As described above, in the magnetic disk apparatus shown in the embodiment 
of FIG. 6, the identification information of the specification of the 
magnetic disk is determined by the ratio of the resistance values between 
the resistor Ru of the first resistor circuit 11 and the resistor Rd of 
the second resistor circuit 12. Detailed magnetic disk information can 
thus be given by packaging proper resistors Ru, Rd in the fabrication 
process of the magnetic disks. 
In the embodiments described above, as explained with reference to FIG. 8, 
combinations of the resistance value Rd of the first resistor circuit 11 
and the resistance value Ru of the second resistor value 12 are changed in 
order to produce 32 different partial voltage values. Another possible 
method of producing the different 32 partial voltage values is to fix the 
resistance value of one of the resistor circuits and to change only the 
resistance value of the other resistor circuit. 
For example, FIG. 10 is a table showing the partial voltage values at the 
junction point 13 of the first resistor circuit 11 and the second resistor 
circuit 12, examples of the resistance value Rd of the first resistor 
circuit 11 for realizing the partial voltage values, and examples of 
digital outputs of the A/D converter 14 corresponding to the partial 
voltage values, respectively, in the case where the resistance value of 
the resistor Ru of the second resistor circuit 12 is fixed in the magnetic 
disk apparatus according to the invention. In this example also, the 
digital output signal of the A/D converter 14 is 5 bits. According to this 
embodiment, each partial voltage value assumes one of the values equal to 
one to 32 times 1/33 of the reference voltage Vref and assumes a maximum 
value lower than the reference voltage Vref. FIG. 11 is a table showing 
still another example of the identification of the characteristics of the 
magnetic disk apparatus stored in the ROM 15 of FIG. 6. In this example, 
the number of bits of the digital signal output from the A/D converter 14 
is 11. According to this embodiment, therefore, a total of 2048 
(=2.sup.11) combinations of head IC suppliers, the number of the heads, 
the head characteristics, the number of the magnetic disks, the magnetic 
disk characteristics and the customized information can be identified. 
Now, an explanation is given of the operation of the MCU 4 when the 
change-over switch 17 is open. In the configuration of FIG. 6, once the 
change-over switch 17 opens, a voltage proportional to the internal 
temperature of the housing of the magnetic disk apparatus is generated at 
the junction point 13 as an output of the temperature sensor 16. The MCU 4 
is adapted to open the change-over switch 17 and thereby check the 
internal temperature of the housing by monitoring the output of the A/D 
converter 14 at regular intervals of time. 
The partial voltage of the output voltage of the temperature sensor 16 
corresponding to the internal temperature of the housing and the values of 
the digital signal output from the A/D converter 14, as described with 
reference to FIG. 8 or 10, is also set at a value corresponding to the 
temperature at the junction point 13. FIG. 12 is a table showing an 
example of the relation between the digital values stored in the ROM of 
FIG. 6 and the temperature characteristic of the magnetic disk apparatus. 
In this example, the internal temperature of the housing is classified 
into five stages and the output voltage of the temperatures sensor is also 
classified into corresponding five stages. According to this embodiment, 
the five temperature stages are represented by the three bits including 
the ninth to seventh bits of the digital signal output of the A/D 
converter 14. If the output voltage of the temperature sensor 16 is 
further divided, the internal temperature of the housing can be detected 
more finely. 
In this case, the MCU 4 can determine the internal temperature of the 
housing with reference to the ROM 15 based on the digital signal output 
from the A/D converter 14. The write current to the head IC 20 is 
determined by the MCU 4 from the temperature data thus obtained, and a 
control signal is sent to the read/write circuit 21 of FIG. 6 for setting 
the write current value. As a result, the optimum write current can always 
be selected even under different environments after shipment as well as in 
the manufacturing process of the magnetic disk apparatus. 
The A/D converter 14 can be built into the MCU 4. In that case, the input 
terminals of the MCU 4 need only two including a terminal for connecting 
the reference voltage Vref and a terminal connected to the junction point 
13. 
In the above-mentioned embodiment, the output of the A/D converter 14 can 
have an arbitrary number of bits. Also, in spite of the fact that the 
identification information shown in FIG. 11 defines the characteristics of 
the first to fourth heads with 0 and 1 using the seventh to fourth bits, a 
program can be produced ignoring the third and fourth heads, for example, 
in the case where only two heads, the first and second heads, are present. 
As described above, in the magnetic disk apparatus according to the first 
aspect of the invention, both the printed board and the circuit from head 
to actuator include resistor circuits connected in series, and the partial 
voltage appearing at the junction point of the two resistor circuits is 
A/D converted, so that the resulting digital value is recognized to 
identify the various specification information of the magnetic disk. 
The magnetic disk information identified by the control circuit is 
recognized by a tester in the manufacturing process. In this way, a proper 
program code or a read/write parameter can be written without reading a 
label. Also, detailed data can be supplied for quality control, etc. of 
the magnetic disk apparatus. 
Further, in the magnetic disk apparatus according to the second aspect of 
the invention, the internal temperature of the housing of the magnetic 
disk apparatus is detected, and the write current to the heads can be 
optimally controlled by the control circuit based on the detected 
temperature. The read/write characteristic can be improved and the write 
characteristic to the magnetic disk can be stabilized without causing any 
write expansion.