Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!VAX.FTP.COM!jbvb
From: jbvb@VAX.FTP.COM (James Van Bokkelen)
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: CHEAP ethernet cards
Message-ID: <8902171625.AA17955@vax.ftp.com>
Date: 17 Feb 89 16:25:14 GMT
References: <8Xylj3y00UoJA85VpL@andrew.cmu.edu>
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In the testing I have done, the shared-memory cards are almost always faster
than the DMA or programmed-I/O cards, on AT class machines.  AT DMA is
crippled, and programmed I/O appears to be slower than REP MOVSW.  Presumably
the shared memory costs somewhat in terms of bus arbitration and possibly
faster or more expensive RAM chips; I am not a hardware engineer.  Of course,
space for shared memory is likely to be scarce on some machines, DMA is even
scarcer (unless you add AT bus fingers), so some vendors just use I/O ports.
W-D has never told me why they didn't use the Nat Semi design, but then again,
3Com didn't use it for the 3C503 (which does shared memory, DMA and I/O all
on the same card) either.

James B. VanBokkelen		We're moving.  After 2/26, the new number
FTP Software Inc.		will be (617) 246-0900.