I have been persistent with a thought to perform my first BIOS update ever through MS-DOS but have been postponing this task until today. Despite people telling me any bootable ISO will do it either through CD-ROM or RAMDRIVE, I am still having problems. First is the problem with CD-ROM driver trying to make it work with 4 driver files (cd1.SYS, cd2.SYS, cd3.SYS, cd4.SYS) as well as starting RAMDISK proved to be failure:

CD-ROM XMS Allocation Error

RAMDISK XMS Allocaton Error (X: and R: drives not working)

This A20 line seemed to be the obstacle which then after a couple of searches pointed me to this article on Microsoft website. It seems that FastGate is the culprit which takes over A20 line and conflicts with himem.sys which should be handling it causing the driver to be unable to allocate memory resources. Albeit article suggests 2 workarounds which is disabling FastGate option or adding switch, I read that the former workaround could cause problems which involves later tinkering BIOS, disabling shadow copy etc. while the latter workaround can just hang system as stated in the link above. I assume it just hangs the boot process from image file though.

Summing up the above, I am cautious and think it is risky to follow both workarounds because disabling FastGate or trying adding switch by trying available switches from 1-14 or 16, could crash the BIOS update process by itself. I could do this without the need for himem.sys with bootable USB thumbdrive by making it to be seen as USB-HDD, but some time ago I read that it is never a good idea to update BIOS from hard drive so even thought it is simulation, who knows... Maybe it will deactivate hard drive in the middle of the BIOS update process or even USB thumbdrive per se? One forum discussion was about updating BIOS and somebody suggested to not load himem.sys for some reason, but now that I think of it, what if BIOS update needs upper memory?