Mail Archives: opendos/2000/10/31/16:17:22
----- Original Message -----
From: "Da Silva, Joe" <Joe DOT daSilva AT emailmetering DOT com>
To: <opendos AT delorie DOT com>
Sent: Monday, October 30, 2000 10:55 PM
Subject: RE: 1024 cylinder limit; anti-bloat (was DRDOS FDISK)
> [da Silva, Joe]
>
> Well, yes and no. The limit is in the Int 13 interface defined
> between the BIOS and the O/S. Many BIOSes from the mid
> 90's would happily accept cylinder counts > 1024 but this
> was totally useless because they still used an untranslated
> Int 13 interface. Later, they realized that providing translation
> would be a "good idea" ... <g>
>
> The real mistake IBM made was to define the Int 13 CHS
> parameters with different limits to those of the MFM hardware
> interface (which was later transformed into the ATA interface).
> Now, the ATA interface CHS parameters (also the LBA ones)
> define up to 128G, while the Int 13 interface defines up to 8G.
> But, because IBM mismatched the two, the net effect was a
> 504M limit. BIOSes today get around this mismatch by
> translating the CHS parameters, thereby allowing the Int 13
> interface to address the full 8G (with only 1024 cylinders),
> beyond which the standard Int 13 interface (as used by
> DR-DOS, etc.) cannot take us (for that, a newer, Extended
> Int 13 interface was defined).
That is one of the reasons why I don't like ATA drives anyway. I use SCSI
and don't worry about it. Although my current controller has a 4GB limit per
drive because it was designed to use int 13h to be compatible with IDE. When
I get the new controller and get ultar wide drives installed, I'll get rid
of the single IDE drive in my system. Everything else I have is SCSI: Tape
drive, Syquest drive, CDROM drive and second hard drive.
My old RLL drive ran as fast as most IDE drives did anyway. Of course these
newer 33Mhz and 66Mhz have some decent spped, SCSI is still faster.the U2W
drives and controller will work at 80mbs and the newer U3W will run at
160mbs which is 60% fater than fiber optice drives and interfaces.
> As for the 1024 limit itself, yes in retrospect, it could have
> easily been avoided, however, nobody would ever dream that
> drives would exceed 8G, so this is really not something to
> blame IBM for - just the silly mismatch ...
Or back then when IBM wrote the BIOS 504MB! That would have been 50 times
what the most common drives were at that time in fact many people were using
5MB drives.
> [da Silva, Joe]
>
> Don't know ... never used DR-DOS 5 ... however, I suspect the
> DR-DOS 6 executables would be of similar size (there may be
> more of them perhaps, but you could always delete anything
> you never use). DR-DOS 6 ran very nicely on 8088 machines,
> with the exception of DOSBOOK, which "ran like a dog" on
> anything less than a 286 ...
The kernel files would be smaller and it did have the Task Swap in it as
well. The major difference was the memory management. This is why many
people prefered to use DOS 3.3 and not move up to MSDOS 5.0. Unless you had
a special 286 with EMS capability there was no real reason to move. But
today with these large drives a person would probably want to move to DRDOS
5.0.
Just a historical item here: I have a copy of WYSE DOS 3.2 that also broke
the 32MB barrier and of course it was written by MS. It is not compatibile
with the way 3.3 does it but MS was holding back. I also understand the
Compaq DOS 3.2 also had similar features.
Pat
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