On 09/29/2017 11:20 AM, Jon Elson via cctalk wrote:
I can only imagine a real AT would be even less likely to handle a drive
over about 40 MB.
40MB would not be much of a problem.
DOS, through 3.30 had a limit of 32MB per partition, but you could upgrade
to newer DOS, or break it up into multiple partitions. An ST250 (40MB)
could be two 20MB, or a 32MB and an 8MB, depending on your type of need.
An ST4096 (80MB) could be 3 partitions.
On Fri, 29 Sep 2017, Jules Richardson via cctalk wrote:
I think the limit was normally 512MB in the old c/h/s addressing days,
wasn't it? For a connected drive, the BIOS set aside 4 bits for the number
of heads per cylinder, 6 bits for the sectors per track, and 10 bits for
the number of cylinders - i.e. maximums of 16, 64 and 1024. At 512 bytes
per sector, that came out as 512MB.
In addition, there used to be a 2GB limit imposed by DOS. It should have
been a 4GB limit, but they used a SIGNED long int, instead of unsigned, so
the size of the drive could be from -2147483648 to 2147483647 bytes.
Similarly file size was from -2147483648 to 2147483647. If you stepped
on a directory entry, you could change a file size to be NEGATIVE!
OK, change a file on a floppy to have a file size of 8000 0000h. DOS now
reports it as -2147483648. Or FFFF FFFFh (-1). Copy a negative sized
file to the drive and that should increase the free space, right?
Didn't work.
Older BIOS firmware provided no means for the user to define the geometry
of a connected drive - just a list of predefined types, and those often
maxed out at far less than any 512MB limit. There were various software
solutions to get around it, though.
Of course operating systems had various limits on the maximum size of a
partition on top of that - e.g. I think it was 32MB in earlier versions of
MS-DOS.
What are the current drive size limits?
