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From: anderson@allvax.enet.dec.com (Dave Anderson)
Newsgroups: comp.sys.mac.hardware
Subject: Virtual Memory / hardware deficiencies (was Re: New Macintosh Strategy)
Message-ID: <3348@ryn.esg.dec.com>
Date: 30 Oct 90 16:52:51 GMT
Sender: guest@ryn.esg.dec.com
Distribution: comp.sys.mac.hardware
Organization: Digital Equipment Corporation
Lines: 34


In article <1990Oct30.075308.15261@world.std.com>, boris@world.std.com (Boris Levitin) writes...
>                                           ... especially considering that
>the virtual part of that RAM will be unbearably slow (I've used Ready-Set-Go
>with its down-your-throat VM facility, and I've tried Word's load-only-used-
>portion-of-document thing, and as a result, I'm less excited about VM than
>practically any other System 7.0 feature).

Virtual memory doesn't have to be a dog (for at least 20 years I've been using
systems that depend heavily on VM and still provide good performance), but for
reasonable performance it requires both good algorithms and fast disk I/O.  I
strongly suspect that the complaints about it on the Mac are due to the lack of
DMA on the SCSI port; this causes a major cpu hit every time the disk is 
accessed, as well as limiting the data transfer rate.

Does anyone know why Apple insists on building machines with designs that
probably aren't a problem for a strictly single-tasking system but are
downright *stupid* for a multitasking system (which the Mac has been ever since
multifinder was invented)?  When the IIfx came out I had hopes that they'd
finally woken up, but the new machines are right back to the apparent attitude
of 'it doesn't matter how badly the machine is crippled as long as costs are
cut by a few dollars'.  Even the crummiest PC-clone offers DMA (not a great
implementation, but still orders of magnitude better than what Apple offers) --
it's not very expensive.

This is all very frustrating for me -- I need to buy a home system 'yesterday'
but there's nothing reasonable out there.  I can't stomach the idea of getting
a PC (the Mac environment is just too far ahead), but Apple refuses to build
decent hardware (and even if they did, we'd probably have to wait for system 17
or so before they actually made use of it).

	Dave

[The above is my opinion only, I know of no-one else who would want it.]