Disk drive testing method and apparatus

• US 4,725,968 A
• Filed: 05/14/1985
• Issued: 02/16/1988
• Est. Priority Date: 05/14/1985
• Status: Expired due to Fees

• Current Assignee: Nicolet Instrument Corporation (Thermo Fisher Scientific Incorporated)
• Original Assignee: Nicolet Instrument Corporation (Thermo Fisher Scientific Incorporated)
• Inventors: Heist, Barry G., McKinney, Michael J., Baldwin, Dale B.
• Primary Examiner(s): Gruber, Felix D.
• Assistant Examiner(s): Black, Thomas G.
• Application Number:
  US06/734,020
• Time in Patent Office: 1,008 Days
• Field of Search: 364/550, 364/900, 360/77, 360/78, 360/25, 360/31, 371/21
• US Class Current: 702/186
• CPC Class Codes: G06F 11/2221 to test input/output devices or peripheral units
• CPC Class Codes: G06F 11/32 with visual or acoustical indication of the functioning of the machine
• CPC Class Codes: G06F 11/3485 for I/O devices
• CPC Class Codes: G11B 20/1816 Testing
• CPC Class Codes: G11B 5/59633 Servo formatting G11B5/59627, G11B5/59677, G11B5/59683, G11B5/59688 take precedence

Abstract

A disk drive testing apparatus (20) is disclosed which provides substantially automatic cycling through various tests of disk drive units. A graphical display is provided on a screen (25) to the operator to allow the operator to determine whether the disk drive is performing in or out of specifications which may be read into the apparatus from an EEPROM memory module (26). By pressing a single TEST switch (22) on the tester, the operator can cycle through a preselected series of tests on the drive unit. The tester 20 is controlled by a microcomputer central processing unit (42) to cycle through the tests and to provide a display on the screen (25) for selected tests which includes a graphics field defining a performance reference frame including a geometric target specification position, a geometric pass range, and a geometric fail range. A figure is superimposed on the graphics field which is displaced geometrically from the target specification position by a distance which is directly related to a performance variable determined by comparing a signal from the disk drive with a specification reference. The tester also provides an analysis of the probability of disk reading and writing errors and displays a graph (365) illustrating the likelihood that data bit timing from the disk drive will remain within selected window margins over long periods of time.

Claims

1. A method of testing a disk drive unit in cooperation with a test disk in the drive unit to evaluate a selected performance characteristic of the disk drive unit, comprising the steps of:

(a) operating the disk drive unit such that a selected test is performed on the drive unit in cooperation with the test disk and signal indicative of the performance of the drive unit on the test is provided by the drive unit;

(b) comparing the signal from the drive unit to a predetermined specification for the signal to determine a performance variable which is related to the deviation of the signal from the drive unit from the specification for the signal;

(c) displaying to the operator on a display device a graphics field which defines a peformance reference frame including a geometric target position corresponding to the reference specification, a geometric pass range, and a geometric fail range;

(d) displaying to the operator a cursor figure on the display device which is superimposed on the graphics field and which is displaced geometrically from the target specification position by a distance which is directly related to the performance variable, wherein the drive unit has a photodetector which provides an output index pulse once every revolution of the diskette, and wherein the selected test performed on the drive unit is determination of spindle rotation speed in which the output index pulses from the photodetector in the drive unit are counted to determine the spindle rotation speed, and wherein the spindle rotation speed so determined is compared to a predetermined specification speed for the signal to determine a spindle rotation performance variable, and wherein a reference frame is displayed to the operator including a linear scale representing a range of spindle rotational speeds and a pass band of speeds within that range centered about the specification speed, and wherein a cursor figure is superimposed on the graphics field above the linear scale which is displaced from the position on the scale of the specification speed a distance proportional to the spindle rotation performance variable.

2. A method of testing a disk drive unit having a reading head in cooperation with a test disk in the drive unit to evaluate a selected performance characteristic of the disk drive unit, comprising the steps of:

(a) operating the disk drive unit such that a selected test is performed on the drive unit in cooperation with the test disk and a signal indicative of the performance of the drive unit on the test is provided by the drive unit;

(b) comparing the signal from the drive unit to a predetermined specification for the signal to determine a performance variable which is related to the deviation of the signal from the drive unit from the specification for the signal;

(c) displaying to the operator on a display device a graphics field which defines a peformance reference frame including a geometric target position corresponding to the reference specification, a geometric pass range, and a geometric fail range;

(d) displaying to the operator a cursor figure on the display device which is superimposed on the graphics field and which is displaced geometrically from the target specification position by a distance which is directly related to the performance variable, wherein the selected test performed on the drive unit is determination of the track 00 switch position, and wherein the signal provided from the drive unit is the output from the track 00 switch which is sensed as the head is moved past the track 00 sensor switch position, and wherein the position at which the track 00 switch triggers with respect to the tracks on the test diskette is compared with a specification track position at which the track 00 switch should be triggered to determined a performance variable directly related to the difference between the sensed track 00 sensor position and its specification position, and wherein a graphics field is displayed to the operator composed of a linear scale with gradations thereon indicating the relative position of the outer tracks on the diskette including track 00, and a pass band centered about the desired track position of the track 00 switch, and wherein the cursor figure superimposed on the graphics field is a cursor arrow above the linear scale which is displaced along the scale away from the specification track position from the track 00 switch a distance proportional to the performance variable.

3. A method of testing a disk drive unit having a reading head in cooperation with a test disk in the drive unit to evaluate a selected performance characteristic of the disk drive unit, comprising the steps of:

(a) operating the disk drive unit such that a selected test is performed on the drive unit in cooperation with the test disk and a signal indicative of the performance of the drive unit on the test is provided by the drive unit;

(b) comparing the signal from the drive unit to a predetermined specification for the signal to determine a performance variable which is related to the deviation of the signal from the drive unit from the specification for the signal;

(c) displaying to the operator on a display device a graphics field which defines a peformance reference frame including a geometric target position corresponding to the reference specification, a geometric pass range, and a geometric fail range;

(d) displaying to the operator a cursor figure on the display device which is superimposed on the graphics field and which is displaced geometrically from the target specification position by a distance which is directly related to the performance variable, wherein the selected test performed on the drive unit is index pulse sensor position, wherein the diskette contains an opening therein to allow light to pass therethrough to trigger an index pulse photodetector in the drive unit and has data recorded on a track on the disk at a predetermined position with respect to the index hole in the disk, and wherein the time difference between the time that the index pulse signal received from the photodetector and the time of sensing by the reading head of the signal recorded on the disk is compared to a specification time difference for the signal to determine a performance variable directly related to the difference between the specification time delay and the actual time delay, wherein the graphics field displayed to the operator is composed of a linear scale with gradations thereon and a pass band on the linear scale centered about the position of the desired delay time, and wherein the cursor figure displayed to the operator is a figure superimposed above the linear scale which is displaced along the scale from the specification time delay a distance proportional to the performance variable.

4. A method of testing a disk drive unit having a reading head in cooperation with a test disk in the drive unit to evaluate a selected performance characteristic of the disk drive unit, comprising the steps of:

(a) operating the disk drive unit such that a selected test is performed on the drive unit in cooperation with the test disk and a signal indicative of the performance of the drive unit on the test is provided by the drive unit;

(b) comparing the signal from the drive unit to a predetermined specification for the signal to determine a performance variable which is related to the deviation of the signal from the drive unit from the specification for the signal;

(c) displaying to the operator on a display device a graphics field which defines a peformance reference frame including a geometric target position corresponding to the reference specification, a geometric pass range, and a geometric fail range;

(d) displaying to the operator a cursor figure on the display device which is superimposed on the graphics field and which is displayed geometrically from the target specification position by a distance which is directly related to the performance variable, wherein the selected test is the centering of the disk on the disk drive spindle, wherein there is a signal of constant amplitude written on one of the tracks of the test disk, and wherein the signal indicative of the performance of the drive unit is the reading signal from a head on the drive reading the signal track thereon, and wherein the magnitude of the signal from the drive unit is compared to a constant magnitude specification for the signal to determine the maximum deviation of the drive unit signal from the constant magnitude specification and a performance variable is calculated proportional to the magnitude of the maximum deviation of the drive unit signal from the constant magnitude signal, and wherein the graphics reference field displayed to the operator is a circular line corresponding by analogy to the central opening in the diskette, and wherein the cursor figure displayed to the operator is a smaller circle within the outer reference frame circle which is displaced from concentricity with the outer circle by a distance proportional to the performance variable indicative of the magnitude of the deviation from a constant signal and such that the outer reference frame circle defines the boundaries of the specification pass band area.

5. A method of testing a disk drive unit having a reading head in cooperation with a test disk in the drive unit to evaluate a selected performance characteristic of the disk drive unit, comprising the steps of:

(a) operating the disk drive unit such that a selected test is performed on the drive unit in cooperation with the test disk and a signal indicative of the performance of the drive unit on the test is provided by the drive unit;

(b) comparing the signal from the drive unit to a predetermined specification for the signal to determine a performance variable which is related to the deviation of the signal from the drive unit from the specification for the signal;

(c) displaying to the operator on a display device a graphics field which defines a peformance reference frame including a geometric target position corresponding to the reference specification, a geometric pass range, and a geometric fail range;

(d) displaying to the operator a cursor figure on the display device which is superimposed on the graphics field and which is displaced geometrically from the target specification position by a distance which is directly related to the performance variable, wherein the selected test performed on the drive is the test of the resolution of the reading heads, wherein the drive unit is operated to write signals on the disk at a lower frequency and a higher frequency on two tracks, and wherein the output signals indicative of the performance of the drive are the signals provided by the head when reading each of the two tracks, and wherein the amplitudes of the signals from the reading head for the two tracks are compared to each other to provide a ratio of amplitudes and wherein the ratio is compared to a predetermined specification for the ratio to determine a performance variable directly related to the magnitude of the deviation of the ratio from the specification ratio, and wherein a graphics reference field is displayed to the operator which is composed of inner and outer concentric circles defining between them a pass band for the ratio of the higher and lower frequency signals, and wherein the cursor figure superimposed on the graphics field is an array of concentric circular images which extend outwardly from a position within the inner circle to a position which is a radial distance outward which is directly proportional to the performance variable and such that the circular images will extend out into a position within the pass band between the two reference frame circles if the ratio is within specification and will be withdrawn within the inner circle or extend beyond the outer circle if the ratio is outside of specification.

6. A method of testing a disk drive unit having a reading head in cooperation with a test disk in the drive unit to evaluate a selected performance characteristic of the disk drive unit, comprising the steps of:

(a) operating the disk drive unit such that a selected test is performed on the drive unit in cooperation with the test disk and a signal indicative of the performance of the drive unit on the test is provided by the drive unit;

(b) comparing the signal from the drive unit to a predetermined specification for the signal to determine a performance variable which is related to the deviation of the signal from the drive unit from the specification for the signal;

(c) displaying to the operator on a display device a graphics field which defines a peformance reference frame including a geometric target position corresponding to the reference specification, a geometric pass range, and a geometric fail range;

(d) displaying to the operator a cursor figure on the display device which is superimposed on the graphics field and which is displaced geometrically from the target specification position by a distance which is directly related to the performance variable, wherein the selected test performed on the drive is the test of radial alignment of the disk drive head, wherein the test disk has a prerecorded tracks with the signal thereon recorded in a non-concentric position on the disk such that the head, when reading the tracks, will provide an output signal having a magnitude varying in time with the displacement of the tracks toward and away from the head as the diskette rotates, and wherein the output of the reading head is the signal indicative of performance of the drive, and wherein the magnitude of the signal from the head over a revolution of the diskette is examined to locate the two maximum peaks of magnitude of the signal from the head which magnitude peaks are then compared to one another to provide a lobe ratio, and wherein the ratio is compared to a specification ratio to determine a performance variable which is directly proportional to the difference between the lobe ratio so determined and the specification ratio, and wherein the graphics field reference frame displayed to the operator is a linear scale with gradations thereon and intersecting portions of circular lines geometrically analogous to separate tracks on the disk, and wherein the cursor figure superimposed on the graphics field is a solid figure geometrically analogous to the head of the disk drive which is displaced along the linear scale away from the intersection of the circular line representing the desired track position a distance which is related to the performance variable.

7. The method of claim 6 in which the area covered by the cursor figure representing the head on the disk drive is chosen such that the radial head alignment of the head will be within specification as long as any part of the cursor figure representing the head intersects the circular line segment representing the track on which the head is to be centered.

8. A method of testing a disk drive unit having a reading head in cooperation with a test disk in the drive unit to evaluate a selected performance characteristic of the disk drive unit, comprising the steps of:

(a) operating the disk drive unit such that a selected test is performed on the drive unit in cooperation with the test disk and a signal indicative of the performance of the drive unit on the test is provided by the drive unit;

(b) comparing the signal from the drive unit to a predetermined specification for the signal to determine a performance variable which is related to the deviation of the signal from the drive unit from the specification for the signal;

(c) displaying to the operator on a display device a graphics field which defines a peformance reference frame including a geometric target position corresponding to the reference specification, a geometric pass range, and a geometric fail range;

(d) displaying to the operator a cursor figure on the display device which is superimposed on the graphics field and which is displaced geometrically from the target specification position by a distance which is directly related to the performance variable, wherein the selected test to be performed on the drive is the azimuth angle of the head with respect to a tangent to the tracks on the disk, and wherein the test disk has plural tracks of signals written on the disk over one revolution thereof at selected different angles with respect to a circle centered on the track to be read by the head such that the magnitude of the signal from the disk read by the head will vary in relationship to the angle of the data written with respect to the head, and wherein the signal indicative of the performance of the drive is the output signal from the reading head, wherein the magnitudes of the bursts of signal read from the head as the head passes over each of the separate tracks of signals written on the disk are compared with one another in a selected sequence to define ratios between the burst magnitudes which are indicative of the orientation of the head with respect to the signals written on the disk, and wherein such ratios are compared to specification ratios to provide a performance variable which is directly related to the angle of deviation of the head with respect to a true circular track on the disk, and wherein the graphics field displayed to the operator includes a linear scale representing by analogy the track center line of a circular track on the disk and shaded sectors of a circular centered on the linear scale and extending over an area corresponding to the pass band of the specification for azimuth angle of the head, and wherein the cursor figure superimposed on the graphics field is a line which rotates about the center of the linear scale at the intersection of the shaded sectors therein and is displaced from the linear scale at an angle directly related to the performance variable indicative of the angle at which the head deviates from a true circular track on the disk.

9. A method of testing a disk drive unit having a reading head in cooperation with a test disk in the drive unit to evaluate a selected performance characteristic of the disk drive unit, comprising the steps of:

(a) operating the disk drive unit such that a selected test is performed on the drive unit in cooperation with the test disk and a signal indicative of the performance of the drive unit on test is provided by the drive unit;

(b) comparing the signal from the drive unit to a predetermined specification for the signal to determine a performance variable which is related to the deviation of the signal from the drive unit from the specification for the signal;

(c) displaying to the operator on a display device a graphics field which defines a peformance reference frame including a geometric target position corresponding to the reference specification, a geometric pass range, and a geometric fail range;

(d) displaying to the operator a cursor figure on the display device which is superimposed on the graphics field and which is displaced geometrically from the target specification position by a distance which is directly related to the performance variable, wherein the selected test performed on the drive unit is a test of the timing between data written on the disk as read by the head, and wherein the signal indicative of the performance of the drive is the output signal from the head composed of digital data, wherein the time between the bits in the data read by the head are determined and compensated to remove systematic large scale variations in timing between adjacent data bits, and wherein the data indicative of the compensated separation between data bits in samples read from the disk are arranged and grouped as a function of deviation from the mean of the compensated separation times to provide a distribution of the deviation of the sampled separation times from the calculated mean time, and wherein a Gaussian distribution is fit to the data so arranged and the Gaussian distribution is compared to specification window margins indicating the maximum deviation of bit timing from the mean which is allowed within specification to determine if the fitted Gaussian distribution intersects the specified window margins at a likelihood greater than a selected threshold value, and wherein a graphics reference field is displayed to the operator composed of a linear scale with gradations indicating the deviation of the bit separation times from the mean separation time and a vertical scale indicating the likelihood that a separation time will be found, and wherein the superimposed cursor figure is a curve of the sample of compensated separation times as a function of the deviation of the sample times from the mean separation time which may be used to predict the probability that a particular separatiion time will be found.

10. A disk drive testing apparatus for testing a disk drive unit having a reading head in cooperation with a test disk in the drive unit to evaluate selected performance characteristics of the disk drive unit, comprising:

(a) means connected to the disk drive unit for controlling the operation of the drive unit in cooperation with the test disk such that the drive unit provides a signal indicative of the performance of the drive unit on a selected test;

(b) a visual display means having a screen on which graphic information may be displayed which is responsive to control signals for displaying graphic patterns on the screen;

(c) control means receiving the signal indicative of performance from the drive unit and a predetermined specification for the signal for comparing the signal from the drive unit and the predetermined specification for the signal to determine a performance variable which is related to the deviation of the signal from the drive unit from the specification for the signal and for providing control signals to the display means to control the same to draw a graphics field which defines a performance reference frame including a geometric target position corresponding to the reference specification, a geometric pass range, and a geometric fail range, and to further draw a cursor figure on the display screen which is superimposed on the graphics field and which is displaced geometrically from the target specification position by a distance which is directly related to the performance variable.

11. The apparatus of claim 10 wherein the control means includes a programmable microcomputer central processing unit, a random access memory for data, a read only memory which contains the program for operating the central processing unit, and a display random access memory which receives display data from the central processing unit into selected positions in the memory which correspond to pixel positions on the display screen and wherein the central processing unit changes the position of the cursor figure on the display screen as the performance variable changes by changing the content of the display memory at the pixel positions of the cursor in correspondence with the changes in the performance variable.

12. The apparatus of claim 11 further including a memory module which contains the performance specifications for the drive unit and which is connected to the central processing unit such that the central processing unit can access the desired performance specifications from the memory module for the selected test being performed on the disk drive unit.

13. The apparatus of claim 12 wherein the memory module is an electronically erasable programmable read only memory and wherein the memory module is detachable from the apparatus to allow another memory module containing different performance specifications for another disk drive unit to be inserted therein and connected to the central processing unit in the apparatus.

14. The apparatus of claim 10 wherein the means for controlling operation of the disk drive does so to test a performance characteristic which is the relative displacement of a physical part of the disk drive unit from its nominal position, and wherein the control means controls the display means to provide a graphics field reference frame to the operator which is a simplified schematic representation of a reference on the test disk with respect to which the physical part is displaced and further controls the display means such that the cursor figure superimposed on the grahics field is a simplified geometric representation of the physical part which is so displaced, whereby the displacement on the display screen of the cursor figure with respect to the reference frame is a geometric analogy to the actual displacement of the physical part.

15. The apparatus of claim 10 wherein the means for controlling operation of the disk drive controls the disk drive to determine the spindle rotation speed and in which the signal indicative of performance of the drive unit is the output index pulses from a photodetector in the drive unit which provides an output pulse once every revolution of the disk, and wherein the control means counts the output index pulses from the photodetector to determine the spindle rotation speed and compares the spindle rotation speed so determined to a predetermined specification speed to determine a spindle rotation performance variable, and provides control signals to the display means to display a reference frame to the operator which includes a linear scale representing a range of spindle rotation speeds and a pass band of speeds within that range centered about a specification speed, and to display a cursor figure superimposed on the graphics field above the linear scale which is displaced from the position on the scale of the specification speed a distance proportional to the spindle rotation performance variable.

16. The apparatus of claim 10 wherein the means for controlling operation of the disk drive operates it to rotate the test disk to allow a test of track 00 switch position and wherein the signal provided from the drive unit to the apparatus is the output from the track 00 switch which is sensed as the head is moved past the track 00 sensor switch position in the drive unit, and wherein the control means compares the signal from the drive unit indicative of the position at which the track 00 switch triggers with respect to the tracks on the test disk to a specification track position at which the track 00 switch should be triggered to determine a performance variable directly related to the difference between the sensed track 00 sensor position and its specification position, and provides control signals to the display means to display a graphics field composed of a linear scale with gradations thereon indicating the relative position of the outer tracks on the disk including track 00, a pass band centered about the desired track position of the track 00 switch, and to display the cursor figure superimposed on the graphics field as a cursor arrow positioned above the linear scale which is displaced along the scale away from the specification track position for the track 00 switch a distance proportional to the performance variable.

17. The apparatus of claim 10 wherein the means for controlling the operation of the disk drive causes it to perform index pulse timing of the index sensor of the drive unit, wherein the disk in the drive unit contains an opening therein to allow light to pass therethrough to trigger an index pulse photodetector in the drive unit and has data recorded on a track on the disk at a predetermined position with respect to the index hole of the disk, and wherein the signals indicative of performance are the index pulse signal and the head reading signal which provides reading of the data recorded on the track on the disk, and wherein the control means determines the time difference between the time that the index pulse signal is received from the photodetector in the drive unit and the time of sensing by the head of the signal recorded on the disk and compares the time difference to a specification time difference for the signal to determine a performance variable directly related to the difference between the specification time difference and the actual time difference, and wherein the control means provides control signals to the display means to provide a display field which is composed of a linear scale with gradations thereon and a pass band on the linear scale centered about the position of the desired time delay, and wherein the cursor displayed to the operator is a figure superimposed above the linear scale which is displaced along the scale from the specification time delay a distance proportional to the performance variable.

18. The apparatus of claim 10 wherein the means for controlling the operation of the disk drive unit does so to test the drive unit for centering of the disk on the disk drive spindle, wherein there is a signal of constant amplitude written on one of the tracks of the test disk, and wherein the signal indicative of the performance of the drive unit received by the apparatus is the reading signal from a head on the drive reading the signal track thereon, and wherein the control means compares the magnitude of the signal from the drive unit to a constant magnitude specification for the signal to determine the maximum deviation of the drive unit signal from the constant magnitude specification and to determine a performance variable proportional to the magnitude of the maximum deviation of the drive unit signal from the constant magnitude signal, and for providing control signals to the display means to display a graphics reference field to the operator composed of a circular line corresponding by analogy to the central opening in the diskette and a cursor figure composed of a smaller circle within the outer reference frame circle which is displaced from concentricity with the outer circle by a distance proportional to the performance variable indicative of the magnitude of the deviation from a constant signal and such that the outer reference frame circle defines the boundaries of the specification pass band area.

19. The apparatus of claim 10 wherein the means for controlling operation of the drive unit does so to test the resolution of the reading head, wherein the test disk has two tracks of signals written thereon at a lower frequency and a higher frequency, and wherein the output signals from the drive unit provided to the apparatus which are indicative of the performance of the drive are the signals provided by the head when reading each of the two tracks and wherein the drive unit is controlled to move the head to read one of the tracks and then the other, and wherein the control means compares the amplitudes of the signals from the reading head for the two tracks to each other to provide a ratio of amplitudes and wherein the ratio is compared to a predetermined specification for the ratio to determine a performance variable directly related to the magnitude of the deviation of the ratio from the specification ratio, and wherein the control means provides control signals to the display means to display a graphics field which is composed of inner and outer concentric circles defining between them a pass band for the ratio of the higher and lower frequency signals and a cursor figure superimposed on the graphic field which is an array of concentric circular images which extend outwardly from a position within the inner circle to a position which is a radial distance outward directly proportional to the performance variable and such that the circular images will extend out into a position within the pass band between the two reference frame circles if the ratio is within specification and will be withdrawn within the inner circle or extend beyond the outer circle if the ratio is outside of specification.

20. The apparatus of claim 10 wherein the means for controlling operation of the drive unit does so to provide a test thereon of radial alignment of the disk drive head, wherein the test disk has a prerecorded track with the signal thereon recorded in a non-concentric path on the disk such that the head, when reading the track, will provide an output signal to the apparatus having a magnitude varying in time with the displacement of the track toward and away from the head as the disk rotates, and wherein the control means examines the magnitude of the signal from the head over a revolution of the disk to locate the two maximum peaks of magnitude therein and to compare the peaks to one another to provide a lobe ratio of the magnitude of the peaks, and wherein the lobe ratio is compared to a specification ratio to determine a performance variable which is directly proportional to the difference between the lobe ratio so determined and the specification ratio, and wherein the control means provides control signals to the display means to provide a graphics reference frame which is composed of a linear scale with gradations thereon and intersecting portions of circular lines geometrically analogous to separate tracks on the disk, and for superimposing a cursor figure on the graphics field which is a solid figure geometrically analogous to the head of the disk drive and which is displaced along the linear scale away from the intersection of the circular line representing the desired track position a distance which is related to the performance variable.

21. The apparatus of claim 20 in which the area covered by the cursor figure representing the head on the disk drive is chosen such that the radial head alignment of the head will be within specification as long as any part of the cursor figure representing the head intersects the circular line segment representing the track on which the head, is to be centered.

22. The apparatus of claim 10 wherein the means for controlling operation of the drive unit does so to provide a selected test of the azimuth angle of the head with respect to a tangent to the tracks on the disk, and wherein the test disk has plural tracks of signals written on the disk over one revolution thereof at selected different angles with respect to a circle centered on the track to be read by the head such that the magnitude of the signal from the disk read by the head will vary in relationship to the angle of the data written with respect to the head, and wherein the output signal from the reading head indicative of the performance of the drive is supplied to the apparatus, wherein the control means compares the magnitudes of the bursts of signal read from the head as the head passes over each of the separate tracks of signals written on the disk with one another in a selected sequence to define ratios between the burst magnitudes which are indicative of the orientation of the head with respect to the signals written on the disk, and wherein such ratios are compared to specification ratios to provide a performance variable which is directly related to the angle of deviation of the head with respect to a true circular track on the disk, and wherein the control means provides control signals to the display means to provide a graphics field including a linear scale representing by analogy the track center line of a circular track on the diskette and shaded sectors of a circle centered on the linear scale and extending over an area corresponding to the pass band of the specification for azimuth angle of the head, and for providing a cursor figure superimposed on the graphics field which is a line which rotates about the center of the linear scale at the intersection of the shaded sectors therein and is displaced from the linear scale at an angle directly related to the performance variable indicative of the angle at which the head deviates from a true circular track on the disk.

23. The apparatus of claim 10 wherein the means for controlling operation of the drive unit does so to provide a selected test of the timing between data written on the disk as read by the head, and wherein the signal indicative of the performance of the drive unit is the output signal from the head composed of digital data, and wherein the control means determines the separation between the bits in the data read by the head and compensates the time difference separations to remove systematic large scale variations in timing between adjacent data bits, and arranges the data indicative of the compensated separation between data bits in samples read from the disk and groups the compensated separation times as a function of deviation from the mean of the compensated separation times to provide a distribution of the deviation of the sampled separation times from the calculated mean time, and werein a Gaussian distribution is fitted to the data so arranged and the Gaussian distribution is compared to specification window margins indicating the maximum deviation of bit timing from the mean which is allowed within specification to determine if the fitted Gaussian distribution intersects the specified window margins at a likelihood greater than a selected threshold value, and wherein the control means provides control signals to the display means to provide a graphics field composed of a linear scale with gradations indicating the deviation of the bit separation times from the mean separation time and a vertical scale indicating the likelihood that a separation time will be found, and providing a superimposed cursor figure composed of a curve on the graphics field which is the compensated separation time from the sample as a function of the deviation of the bit separation time from the mean separation time which may be used to predict the probability that a particular separation time will be found.

24. A method of estimating the likelihood of reading and writing errors of a disk drive unit having a reading head comprising the steps of:

(a) operating the disk drive unit to write a selected data pattern on a track on a disk;

(b) operating the disk drive unit to read the data pattern from the track on the disk on the disk and provide an output signal of digital data read by the head of the disk drive;

(c) counting the separation time between adjacent bits in the signal from the head reading the pattern on the disk and storing the separation times in a memory;

(d) determining a mean separation time of the separation times stored in memory;

(e) determining arrival times within mean window periods centered on the mean separation times;

(f) forming a histogram array composed of multiple cells dividing up the range of arrival times;

(g) assigning to each cell the total number of arrival times which are within the boundaries of the cell; and

(f) displaying the histogram curve of total counts versus arrival time on a display device to an operator.

25. The method of claim 24 wherein steps (a) to (c) are repeated and the number of arrival times in the new sample which fall into the particular cells of the histogram array are added to the previous number in the histogram array to provide a new total for each cell in the array and then clearing the previous histogram array curve from the display device and plotting the new histogram array on the display device showing the total number of separation times in each cell as a function of separation time.

26. The method of claim 24 including the steps of:

calculating the sample mean and sample variance of the count in the histogram array as a function of arrival time from the mean and fitting a Gaussian distribution function to the mean and sample variance so calculated, and comparing the value of the Gaussian distribution at selected window margin times with a selected threshold likelihood, and providing a display to the operator of whether or not the Gaussian distribution so calculated is greater or less than the threshold at the selected window margins.

27. The method of claim 24 including before the step of forming the histogram array, the step of compensating the arrival times for systematic changes over time in the mean separation time and mean window.