486 w/newer IDE drives

Fred Cisin wrote: It really was reserved. No need for quotes. At the 640K barrier lived the video memory for whatever kind of card happened to be there. At the very top of memory was the BIOS. The rest of the space was reserved for ISA cards (which weren't called that until the clones arrived). Even though the 8086/8088 had a dedicated I/O bus, you'd still need to be able to access any ROM extensions on the ISA cards and perhaps whatever shared memory there was available for DMA, etc. The I/O bus just wasn't enough because you of course couldn't execute code via the in/out opcodes and some cards required BIOS extensions to say the least. The 8086/8088's could only address 1MB of memory, so the 640K barrier was a reasonable one at the time despite the infamous "640K ought to be enough for anyone" quote attributed to Mr. Gates. Of course there was nothing to stop you from installing a RAM card in the rest of the I/O space and getting a few more KB, but a better way was to use a memory expansion card and bank switch through a 64K window to access it, which is what the LIM (Lotus, Intel, Microsoft standard was about. That is until 286's came out.