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From: pshuang@ATHENA.MIT.EDU
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Simple Cache Question
Message-ID: <9106062115.AA29501@w20-575-102.MIT.EDU>
Date: 6 Jun 91 21:15:14 GMT
References: <51fde0959.0034237@caen.engin.umich.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
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In answer to your e-mail questions:

o Cache hit ratios cannot easily be measured by programs other than the
cache software itself.  Many (but not SMARTDRV) have a report option
where you can see the current hit ratio for this session.

o Windows does *NOT* ever require you to set SMARTDRV to a large amount,
although it does require you to use HIMEM.SYS; are you confusing the two
different drivers?  Caches tend to top out at about a megabyte;
dedicating more memory than that usually doesn't help performance more
than a tiny fraction, and is not worth it.

o Software tends to run faster directly under DOS than under Windows for
several reasons.  Windows is intercepting all hardware accesses and
mediating to make sure that your DOS application isn't trying to use the
hard disk or writing to video or accessing communications ports at the
same time that another application is, and this eats up CPU cycles.
Also, being in virtual-86 mode of the 80386 (Windows 3.0) as opposed to
being in the real mode (DOS alone) slows down memory access.  The 80386
virtual and protected modes allow hardware protection for memory
accesses so that multitasking programs cannot trash each other as easily
as they might otherwise, but the cost is that instructions which access
memory often run slower due to overhead in checking to make sure that
the program is allowed to access that part of memory.

Singing off,
UNIX:/etc/ping instantiated (Ping Huang).