🚀 go-pugleaf

>First of all, bus master DMA on the ISA bus (which is a local bus, just
>for the 286 instead of the 486) _will_ prevent the CPU from accessing
>main memory. The big deal about having a faster bus is that on a hard
>drive transfer (for example) instead of the CPU grinding to a halt
>(because the bus is being used to capacity) it may still run at
>80% of peak performance. This is a big deal if you're using a
>multitasking OS like OS/2 or whatever.
>
>Dan

  This message has been cross-posted to some of the comp.os... groups
because I'd like to know whether or not they are multitasking when it
comes to disk I/O.

  Okay, have I got this right?!?!?!

(1)
  VL stands for VESA LOCAL right?

(2)
  If an MS-DOS system has a very fast hard drive it still won't notice
that much speedup, if any, because the ISA bus (at 5MB/sec) outruns
just about every available drive's ability to read its media, and
MS-DOS is going to sit around and do nothing until the file has been
read anyway.

  All a VESA system will really do here is improve the performance of
the cache on a caching controller.

(3)
  The real impact of having a VL hard drive controller will be in a
multitasking operating system, but not because disk transfers will be
sped up.  When a DMA transfer is happening on an ISA (and EISA?) bus,
the CPU can't do ANY processing (even from it's cache?) because the
bus is locked.

  A VL card will help a multitasking operating system because there
are processes which are NOT waiting for disk I/O which WOULD get held
up during the slow DMA transfer from an ISA I/O card to memory.

(4)
  Windows 3.1 enhanced mode doesn't count as a REAL multitasking
operating system in this case because it will still sit around doing
nothing while it waits for its disk I/O request to finish up (?).

  Does OS/2, does Linux, does MS-Windows 32 / MS-Windows NT count as
REAL in this sense (no I'm not trying to get flamed)?

Morgan
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