31 Oct
2016
31 Oct
'16
6:55 a.m.
From: Don North
Track 0 is not used by standard DEC software
I wonder why DEC did't use track 0. The thing is small enough (256KB in the
original single-density) that even 1% is a good chunk to throw away. Does
anyone know? (I had a look online, but couldn't turn anything up.)
If I had to _guess_, one possibility would be that track 0 is the innermost
track, where the media is moving the slowest, and as a result it's more
error-prone. Another is that IBM used track 0 for something special, and DEC
tried to conform with that. But those are pure guesses, I would love to know
for sure.
Noel
31 Oct
31 Oct
7:19 a.m.
On Oct 31, 2016, at 9:55 AM, Noel Chiappa <jnc at
mercury.lcs.mit.edu> wrote:
I don't know either. But for what it's worth, this odd addressing carries over to
the RX50. Not exactly, though. Logical block 0 is the first sector on track 1, sectors
are 2:1 interleaved, and there's a 3 sector skew from track to track. The difference
here is that track 0 does get used: it holds the last 10 sectors of the logical address
space. In other words, physical track 0 follows physical track 79.
paul
From: Don North
Track 0 is not used by standard DEC software
I wonder why DEC did't use track 0. The thing is small enough (256KB in the
original single-density) that even 1% is a good chunk to throw away. Does
anyone know? (I had a look online, but couldn't turn anything up.)
If I had to _guess_, one possibility would be that track 0 is the innermost
track, where the media is moving the slowest, and as a result it's more
error-prone. Another is that IBM used track 0 for something special, and DEC
tried to conform with that. But those are pure guesses, I would love to know
for sure. 
8 a.m.
On 31/10/2016 13:55, Noel Chiappa wrote:
I wonder why DEC did't use track 0. The thing is
small enough (256KB in the
original single-density) that even 1% is a good chunk to throw away. Does
anyone know? (I had a look online, but couldn't turn anything up.)
If I had to _guess_, one possibility would be that track 0 is the innermost
track, where the media is moving the slowest, and as a result it's more
error-prone.
Except that track 0 is the outermost track, where the media is moving
fastest, and therefore perhaps the least error-prone. Except that for
many drives, it's where the heads end up after a reset or recalibration,
and on drives where the heads are (almost) always loaded, the one that
will wear most. I've seen floppies with a transparent ring near the
outer edge, and I'm sure many other listmembers have too.
--
Pete
Pete Turnbull
3:08 p.m.
From: Don
North
Track 0 is not used by standard DEC software
I wonder why DEC did't use track 0. The thing is small enough (256KB in the
original single-density) that even 1% is a good chunk to throw away. Does
anyone know? (I had a look online, but couldn't turn anything up.) 
1 Nov
1 Nov
2:53 a.m.
On 10/31/2016 07:45 PM, Al Kossow wrote:
On 10/31/16 3:08 PM, Vincent Slyngstad wrote:
> Isn't there some weird crap in track 0 on DECmate RX01s
It also has the slushware code, aka front panel space code to do
stuff on the IM6100 chip and peripherals. the 6100/6120
have two spaces front panel code space and normal PDP-8 memory.
Allison
It is IBM 3740 table of contents information.
GA21-9182-5_Diskette_General_Information_Manual_Jul80.pdf for the details
2 Nov
2 Nov
1:50 p.m.
On Tue, Nov 1, 2016 at 3:53 AM, allison <ajp166 at verizon.net> wrote:
On 10/31/2016 07:45 PM, Al Kossow wrote:
Isn't the slushware on the last two tracks of the disk, rather than on
track 0?
On 10/31/16 3:08 PM, Vincent Slyngstad wrote:
> Isn't there some weird crap in track 0 on DECmate RX01s
It also has the slushware code, aka front panel space code to do
stuff on the IM6100 chip and peripherals. the 6100/6120
have two spaces front panel code space and normal PDP-8 memory.
2972
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6 comments
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participants (7)
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aek＠bitsavers.org -
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jnc＠mercury.lcs.mit.edu -
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