Calibration timing bands

#A. Field of Invention

#This invention relates to the magnetic recording art and in particular to a novel and improved method for preparing an alignment disc pak.

#Disc paks generally comprise one or more magnetic discs upon which digital information can be recorded and played back by means of a disc drive which includes motive means for rotating the disc, an arm which carries transducers for recording and playing back the information and associated electronics. Information is recorded on the disc in concentric tracks with a typical track density of 100 or 200 tracks per inch dependent upon the disc drive application. The transducer arm is indexable to any one of the recording tracks, there being 202 tracks in one typical disc used in a number of commercial disc drives. Many computer installations include several disc drives to provide additional memory to the internal memory of a central processing unit. It is absolutely essential in such installations that a disc pak recorded on any one of the disc drives be capable of record and/or playback operation on any of the other disc drives without error. This requirement dictates that the transducer arms of all the disc drives be in alignment with one another within certain tolerance limits. Al alignment disc pak is used to accomplish this alignment of the transducer arms of a number of disc drives.

#In the accompanying drawing:

#FIG. 1 is a plan view showing the equipment and the electrical connections employed in the practice of the method embodying this invention; and

#FIG. 2 shows three oscilloscope traces which occur at various stages in the method embodying the invention.

#Referring now to FIG. 1, the method of the present invention employs an alignment disc pak 10, a disc drive 11 and a multi-beam oscilloscope 12. The alignment disc pak 10 is assumed to already have recorded thereon two signals of frequency f1 and f2 (with f1 > f2) in adjacent eccentric bands as described heretofore. The two signals are recorded at a selected track which for the purpose of the present description is assumed to be track no. 73. Typically, the frequency f1 is 2.5197 megahertz; f2 is 2.5 megahertz and the difference or beat frequency (f1 - f2) is 19.7 kilohertz.

#In the first step of the method embodying the invention, one frame of the playback signal for track 73 is displayed on the oscilloscope display surface 13. To accomplish this the playback signal is coupled from the read output of the disc drive to one of the channel inputs of the oscilloscope, herein illustrated as channel A, by way of example. The disc drive index signal is coupled via the disc drive index output to the time base trigger input of the oscilloscope. As is known, the index signal is essentially a pulse marker occurring once per disc revolution to signify a reference or starting point for recording information on the disc. The oscilloscope 12 is then calibrated in the usual manner as per its operating instructions to display a single frame of the playback signal by means of control knobs not shown in FIG. 1.

#In the next step of the method, another beam of the oscilloscope is used to generate on the display surface a time marker. For oscilloscopes having a delayed time base capability, such capability is used to generate the marker. To this end, a delay time base sweep control knob 14 is employd to establish the time base or horizontal width of the marker. It has been found that the time marker width should preferably be on the order of one-half the time width of one period of the beat frequency (f1-f2). For the aforementioned frequency values, the time marker width turns out to be approximately 100 microseconds.