Re: D9060 Hard drive

On Fri, Mar 29, 2013 at 11:43 AM, Michał Pleban <lists@michau.name> wrote:
> Hello!
>
> Teddy wrote:
>
>> I don't understand. It's not a SCSI drive, its a Western Digital MFM drive.
>
> MFM is the technology used to store data on the physical disk. Typical
> are MFM (like PC diskettes) or GCR (like Commodore diskettes).

Yes, but in geek jargon shorthand, MFM also is used to refer to the
ST506/ST412 interface of a 34-pin digital cable (with select and
step/direction signals) and a 20-pin analog cable (with differential
analog head read/write signals).

> SCSI is the interface which the disk uses to communicate with outside
> world. Typical are SCSI or IDE.

Now, yes.  Back in the 1970s and 80s, drives didn't use command-packet
type interfaces.

The physical drive in a D9060/D9090 is a TM602S or TM603S with
a 34/20 pin ST506/ST412 interface.  The main board in the drive
is called the "DOS Board" and has the IEEE interface, CBM DOS,
and a 50-pin SASI interface.  It's the predecessor to SCSI and is
largely pre-SCSI-2 compatible.  The other part in the drive is a
3rd-party board that has a SASI interface on one end and an ST506
interface on the other end.  That one takes the SASI commands
and handles things like stepping the heads, selecting the heads
and converting packetized commands into serialized head data.
It does the actual work of formatting the drive, but under direction
of the DOS Board.

Since real TM602S and TM603S drives are quite hard to find, most
of us have worked with using much more common ST225 and ST251
drives and ignoring 75% of the capacity.  CBM DOS could handle
a filesystem up to 16MB with 8 bits of track and 8 bits of sector
pointers, but AFAIK, nobody is really trying to push the capacities
past the original 5/7.5MB.  For one thing, there are no partitions
or subdirectories, so all your files are in one place.  I don't think
it would be fun to have hundreds and hundreds of files with no
organization.

-ethan

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