RE: Track/Sectors for older Drives, eg D9090

From: Ethan Dicks (
Date: 2003-08-27 16:52:30

> Hi All, thansk for the information so far... certainly helps!
> >Model			D9090		D9060
> >heads per drive		6		4
> >formatted storage
> >capacity per unit		7,47Mb		4,98Mb
> >cylinders(tracks)		153		153
> >sectors/cylinder		128		192
> >sectors per track		32		32
> >blocks per sector		256		256
> I'd seen this info, and hence my confusion.. the work "cylinders" in
> two lines.

It's as we were saying - "cylinders" refers to the number of discrete
steps the head-positioner can make, regardless of the number of
heads.  "sectors/cylinder" tells you how many sectors are available
without moving the heads (since in drive electronics of this era,
the controller first moves the positioner, then, after some settling
time, selects a head and waits for a particular sector to pass by
the heads).

I would like to point out that "blocks per sector" above should read
"bytes per sector"

> By "logical" I was refering to what the programmer would use when
> they sent a U1 or U2 command.

Commodore drive speak comes from a floppy mentality.  All of the
programs and documentation are oriented around single-sided
disks.  When addressing a 2040/4040/2031/1540/1541, it's fairly
straightforward - "Track" means where the head is, and "sector"
means where on the track the data is.  Strictly speaking, even
a 1541 floppy has cylinders - there's just one track per cylinder,
and the number of sectors per track equals the number of sectors
per cylinder (but it's variable depending on the track number, much
the same with modern hard drives).

It's been years since I did any low-level data work with my D9060 or
D9090 (mostly, I've been trying to understand the firmware), but
AFAIK, the number you want to use for "track" is going to be the
cylinder number (i.e. - 0-153 for either drive), and "sector" is
going to range between 1-128 or 1-192, depending on if it's a D9060
or a D9090.  The suggests a limit of 65280 total sectors if you
were re-writing the firmware to support larger drives (16.7 million
bytes or 15.9 honest megabytes).  This would be with an 8-head drive,
using 256 tracks of it.

I'm sorry if "cylinders" is confusing, but in this case, it _is_
the way you have to think of the drive to figure out where stuff

> Come to think of it... do these drives
> support U1, U2 or do they need B-R and B-W???

AFAIK, yes.  It's DOS 3.0, a direct descendent of the DOS used in
the floppy drives.  The main difference is being able to handle
a BAM that grows and doesn't live on a particular, single cylinder

> I was thinking this era in Commodore's history... for example the
> CBM 8250 etc rather than specific mechanisms.

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