8-bit IDE

From: Richard Erlacher <edick_at_idcomm.com>
Date: Mon Apr 17 00:08:07 2000

please see embedded comments below.


----- Original Message -----
From: allisonp <allisonp_at_world.std.com>
To: <classiccmp_at_classiccmp.org>
Sent: Sunday, April 16, 2000 6:44 PM
Subject: Re: 8-bit IDE

> >Frankly, the reason I'm exploring this is because with the 8-bit mode, I
> >don't have to buffer the data at all beyond the on-board data-in and data
> >out buffers at the bus interface. The board I'm using to host the thing
> is
> handy but that feature is not there.
> >From what I read in the standard, this is a normally selectable operating
> >mode for the interface. What's more, only the smallest of drives would
> >appropriate for CP/M on the S-100, since CP/M supports, at most, 120 MB,
> Actually it supports 16 drives of 8mb each for CP/M 2.2 and 32Mb for
> P2dos, Novados, SuprBDOS all support files to 32mb and drives to 1gb.
The really good thing about the latchless and bufferless interface to the
8-bit channel is also readily adaptable to a RAMDISK via the same channel.
That's what makes me hope for the availability of the 8-bit mode as
described in the ATA standard. Using LBA, it's possible to write a 24-bit
sector address to a RAMDISK. An old 8-bit SIMM would do the job nicely.

I'm not fired up about these various OS' (yet) and won't be until I'm sure I
know how to exploit their features. In any case, in a system where I've got
2 floppies, a dummy FDD, and a ramdisk, I can only use 12 logical drives at
a time, since the max is 16, which, if it were all in HDD's would be 96 MB.

Since it appears to be the consensus that all the doc's + all the software
and such for CP/M 2.2 and earlier, take up less than 50 MB, a big drive in
excess of 120 MB would make no sense at all. The Walnut creek CD has only
about 1/5 of its capacity used. So, while it may be possible with a lot of
effort and with the certainty that you'll be out there all by yourself, to
use a bigger drive, what's the point? I mentioned I had a 44MB drive back
in the '80's and even though I had several copies of everything, it was
never even close to half full. So, while I don't doubt that someone could
figure out a way to use a bigger drive rationally, I don't feel motivated to
go out of my way. If the pico-drives I already have will work in 8-bit
mode, then the code I already have will work to operate them. If not, I'll
build up a circuit equivalent to the Tilmann Reh GIDE interface, less RTC.
It's less RTC because I have a different RTC device if I ever want to use
> BUT, the logical drive to physical drive map does not have to be static.
> For example you could only have drives C/D/E/F as mapped to 8mb logical
> drives. Drive C: could be partition 1 and a fixed mapping. Drives D/E/F
> could be mapped to floating partitions anywhere on a very large drive.
> I supported two 71mb MFM drives this way back in 87 under CP/M2.2.
The two 2-1/2" IDE drives I've got for this hard-card thing are both 250 MB,
nominally. If you have a good and inobtrusive way to accomodate that
without reducing the size of the TPA to such extent that I can't run a
normal 64K CP/M and such that I can still use the MT+ v5.5 or so Pascal
compiler for serious work, I'd be interested. I've also got a couple of
2-1/2" (IBM)drives with a 2mm-pin pitch connector with enough pins to be a
SCSI device. I don't know what their pinout is likely to be. I'll have to
look in the standards, since IBM doesn't have them on their site. These are
120 MB in size.
The standard v2.2 CP/M doesn't like logical drives (partitions) bigger than
64K 128-byte sectors. That's 8192 KB. What I'm after is something that
will paste easily into a pretty standard CP/M 2.2. All the other
whatever-dos will have to be denonstrated working properly and properly
documented as well before I'll be interested.
> >handle that much. Back when I used CP/M every day, I owned the largest
> hard
> >disk system on CP/M that I'd ever seen, at 44MB.
> Obviously you've never seen many of the systems I ran or have aquired.
> Likely
> the 44mb limit was based on inavailability of really large drives. Even
> AmproLB has a 45mb SCSI on it and I plan to bump that up to a 160mb. The
> current system I'm building I'm planning will have IDE 250mb drive. Space
> is handy as I can have a 8mb partition for pascal and another for C or
> whatever.
You're right, I haven't seen the systems of the type you describe. That's
because I switched to PC's in about '84. Most of the hard disks I saw in
commercial use with CP/M were about 20 MB. These were sufficient.
Apparently that was a practica size for DEC machines of the time too, since
most of my partner's DEC clients had 11's of some sort, mostly with single
20 MB drives.
> Allison
Received on Mon Apr 17 2000 - 00:08:07 BST

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