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. --Chuck
