apratt@iuvax.UUCP (01/08/84)
#N:iuvax:1500001:000:1232 iuvax!apratt Jan 8 01:29:00 1984 I have what I believe to be a unique disk emulator. It is a hack of the one in the DOS manual, and it works like this: The system board switches are set to 128K, but the machine has 640K inside. The device driver installs itself by turning off parity checking and using the memory from 128K to 640K as a RAM disk. If something goes wrong, I can use ALT-CTRL-DEL; the driver is smart enough to preserve the data that's already there in "protected" memory. The point was that a "reset" switch could be installed, and the IBM could merrily test the memory up to 128K like it's supposed to, and the data in that high partition would not be touched. The rub: a fellow tells me that the first part of the power-up cycle (when "pwr good" goes true from false) is a hardware "clear all memory" signal (NOT in ROM, but in HARDWARE). Can anybody confirm this? Is there any good reason for it? Can it be circumvented? With a little more polish and any request, I will post the mods to the IBM-copyrighted virtual disk device driver to net.sources. The polish will consist of generalization: reading the switches, testing to see how much memory you ACTUALLY have, and carrying on from there. -- Allan Pratt ...ihnp4!iuvax!akp