RL02 Disk Cartridge Problems - why that particular pack is junk

From: Christopher McNabb <cmcnabb_at_4mcnabb.net>
Date: Mon Dec 9 19:12:00 2002

The RL01/RL02 manual that I won on E-Bay last week arrived in the mail
today. It has quite a good write up on the drive formatting, including
the structure of each sector.

The sector format is as follows:

Sector Pulse: 62.5 microseconds, generated by slots on bottom of disk

Header (Described Below)

Data 128 16 bit words, or
     256 8 bit bytes, or
     170 12 bit words

The sector header occurs after the the sector pulse and contains the
sector number, track number, and head number of the sector in the
following format:

Preamble: 47 Zero Bits followed by a 1 bit
Address: 16 bits - Sector: 6 bits
                   Head: 1 bit
                   cylinder:9 bits
Zeroes: 16 bits of zeros
CRC: 16 bits generated by CRC logic when data is written to the sector
Postamble: 16 zero bits

There is also a "guard track" on each side of the data track,whose
purpose is to cause the head to go back to the center of the data track
should it drift.

When a drive is told to seek to a particular sector, it reads the
factory written sector header to determine if it is the correct sector.
If the drive can not find this info quickly enough, it will fault.

Internal drive circuitry prevents the drive from writing to any part of
the header (except the CRC word).

It seems to me that to correctly format one of these disks after a bulk
erasure, you would have to be able to do the following:
1. Correctly position the head - probably the easiest part
2. Write the correct sector header, including addressing
3. Write the guard tracks ( I bet this is the most difficult)
4. Make sure all the header data gets written to the disk in the
required 62.5 milliseconds (one sector requires 625 milliseconds to pass
under the head, the data part of the sector takes 500 milliseconds, the
servo pulse takes 62.5 milliseconds.
5. Create the "Bad Block" file at the end of the disk.

So, looking at the above, I can see where it would very difficult to
format one of these guys using a stock RL01/RL02 drive, even modified.

It may be possible, however, to do it with another manufacturer's 5440
type disk drive, but I'm just guessing.

Christopher L McNabb
Operating Systems Analyst         Email: cmcnabb_at_4mcnabb.net
Virginia Tech                     ICBM:  37.1356N 80.4272N
GMRS: WPSR255                     ARS:   N2UX  Grid Sq: EM97SD
Received on Mon Dec 09 2002 - 19:12:00 GMT

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