Formatting Guidelines The disk drive unit is a soft sectored device that allows the user to define the sector format. When establishing the track format certain rules should be observed to accommodate the physical timing relationships within the drive. Figure 5-5 shows the basic setup of a sector, Table 5-21 shows the disk data format of the WD1010 chip, while Table 5-22 provides byte offset conversion information. The Hard Disk port address offset is 320 (HEX). Gap 1 If head switching occurs at index time, Gap 1 must be set to allow the read ampl if ier to stabil ize. The minimum 1 ength of Gap 1 is 12 bytes. Sync A sync field precedes each addressable record (ID or record).
This field should be wide enough to accommoddate the "lock up" characteristics of the phase-lock-loop within the data separator portion of the controller. Gap 2 Following each sector a gap should be placed to accommodate spindle speed variations between write operations on the same track to prevent overwriting. To accommodate the ±0.5% speed tolerance of the disk drive, Gap 2 should be a minimum of 1 byte for each 32 bytes of data within the sector. Additonally, the user should increase the gap to accommoddate the spin speed- asynchronous frequency variation of the controller generated MFM WRITE DATA signal s.
Gap 3 Th i s gap i s a s pe edt ole ran c e bu f fer for th e en t ire t rae k t 0 ensure that the last sector does not overflow beyond the index. Gap 3 precedes index and should be wide enough to accommodate the spin speed variations of the disk drive (±0.5%) and the frequency variations of the controller generated MFM WRITE DATA signals. Refer to chapter 2, Specifications for more operating data of the hard disk drive unit. 5-39