On Fri, 12 Apr 2024 01:27:54 -0500 "G. Branden Robinson" <g.branden.robin...@gmail.com> wrote:
> Yes, I reckon trapping into the kernel for every byte (or pair of > bytes) written to the screen would indeed have eaten all your > performance, and been pointless when there was no access protection in > any part of the address space anyway. Hmm, well, "trapping in to the kernel" wasn't so expensive because there was no context switch. Yes, interrupt processing was relatively expensive in terms of CPU cycles. I remember implementing XON/XOFF because a 6 MHz 80286 couldn't keep up with a 1200 bps modem. It wasn't 100% pointless to use the BIOS because it gave you a kind of device independence. Different video cards resided at different addresses (above 640K) and had different modes. The BIOS calls insulated the application from some of that. > Perhaps I am not the first to consider the possibility that MS-DOS was > not well thought out. I do seem to recall having seen other criticism prior, yes. ;-) I'm the last one to defend it; present day Windows systems still suffer from brain-dead choices in MS-DOS that ignored contemporary OS thinking at the time. But it's also a "he is us" problem: MS-DOS vanquished numerous alternatives not because it was better but because it offered so little. Except for the "disk" part, applications largely ignored it. They wrote to the hardware, and were faster for it. The market for well architected slow systems is vanishingly small. If in doubt, ask IBM about TopView. Thanks for the pictures. Among the ridiculous things I keep on my bookshelf are IBM's BIOS reference, and Volume 1 of the 3-volume set for Windows 1.03, obtained free with a $500 ticket to 1-day seminar put on by Microsoft to promote it. Debugging by the light of an ADM-3A. Those were the days! --jkl
