please see embedded comments below.
Dick
----- 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
be
> >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
CP/M3.
> 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
one.
>
> 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
my
> 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.
>
<snip>
> Allison
>
>
>
Received on Mon Apr 17 2000 - 00:08:07 BST