Int 13h buffer 64k boundaries

Chuck Guzis cclist at
Wed Apr 18 23:50:39 CDT 2018

Really?  64K boundary issues cropping up in MS-DOS?

Egad, that would have been known in DOS 1.0.  Certainly, for anyone
writing his/her own low-level disk I/O, it was obvious.

Now, I'll add that if you wrote your own specialized device driver, DOS
did not guarantee handing your driver a buffer that obeyed the 64K
boundary rule.  I suspect that some DOS errors were reported to MS
because of third-party driver bugs.

And if you wrote a low-level driver that used 16-bit I/O, the magic
number was 128K.

But even in the earlies DOS 2.0 device drivers that I wrote, I included
code to split the transfer up to get around the 64K problem if needed.


More information about the cctalk mailing list