31 Jan
2006
31 Jan
'06
6:11 p.m.
On 1/31/2006 at 7:46 PM Michael B. Brutman wrote:
Chuck - you mentioned that the superio controller card
would have a BIOS
extension. Are you certain? One card that I tried definitely did, as
it had the intelligence to handle larger drives.
Some controller cards have BIOS extensions, some don't. Most IDE ones that
were built to handle larger IDE drives do; garden-variety ones don't.
You may get in a bind with a larger IDE drive as the original AT was pretty
limited in its support for large drives.
I was thinking that if each instruction takes a few
cycles that even the
tightest of loops would waste a lot of cycles, but I found a gem in the
286 user's guide - REP. Apparently you can use REP INx and REP OUTx
instructions to generate a tight loop that doesn't require subsequent
instruction fetches until the loop ends. So that would allow a 286 to
push the bus much harder than an 8088/8086 class machine would. (The
8088/8086 would have to keep fetching instructions, which would suck.)
As I mentioned, the operative instructions are INS and OUTS--work just like
STOS and LODS, except the input is through port (DX). Even on a
Pentium-class machine, the original AT 16-bit bus timings are observed for
ISA devices, so at some point, processor speed just doesn't matter any
more.
Cheers,
Chuck