ISA bus throughput
cclist at sydex.com
Tue Jan 31 20:11:04 CST 2006
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
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