3.5" Altair CP/M

[Fred Cisin]

> > > Its an MDL-1011D with an FD1771-B01.
> > > What's the deal with this chip?  Is it formatting the the disk as 360k?
> >Nothing special.  It is a SINGLE DENSITY (FM) ONLY chip.
> >Although it might give a final capacity of 360K or thereabouts,
> >It's parameters are most certainly NOT the same as the IBM "360K" format.
> >It is most likely formatting it as 10 256 byte sectors per track,
APPARENTLY not, that would give about 100K

> >or as 18 128 byte sectors.
> >Tools for looking at MFM disks would be looking for MFM. NOT FM, and would
> >prob'ly default to expecting 512 bytes per sector.

On Sun, 3 Jun 2007, Grant Stockly wrote:
> I found that I have to cover the hole or I get BDOS erros about missing
> sectors.  I figured it wouldn't look for the hole...

The "media type" hole on a 1.4M?
There exist some drives that ignore the "media type" hole, pqrticularly
many/most? of the ones that IBM used in the PS/2s.  They rely on the disk
controller board to tell them when to go to reduced current.

or the index hole on a 5.25"?

> A freshly formatted disk gives me this:
> A>STAT B:
> BYTES REMAINING ON B: 69K
> 69k for a 1.4MB disk!  I was ripped off!  : (  It is running CP/M 1.4.  I
> have the sources if anyone is interested.

Did 1.4 support the DSK option of STAT?  It gives some more info about the
format.
If so, try
B:
A:STAT DSK:

> This is what it says when it boots up:
> TARBELL 24K CPM V1.4 OF 7-20-79
> 2SIO MINIFLOPPY VERSION.
> HOW MANY DISKS? 2
> Were single sided single density 5.25" disks ~70k?

YES.  SSSD 5.25" could range from that up to about 100K.

Is it using 35 tracks (SA400) or 40 tracks?

Most PC floppy controllers will not handle FM/Single density.  Use Dave's
test program on your PC to see if you have a chance.

In addition, it may be writine 128 byte sectors, which leaves out a lot
more of the NEC type FDC chips.

If you have access to a TRS80 Mod 3 or 4, TRAKCESS would be a good tool
for analyzing these disks.  It is mostly in BASIC, so it canbe easily
modified for additional functionality.

> The 3.5" drive does
> sound different than it usually does.  : )

It's not used to getting a pause between seeks, and not getting beaten
half to death by a thrashing OS.

--
Grumpy Ol' Fred     		cisin at xenosoft.com