Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!pasteur!ucbvax!XX.LCS.MIT.EDU!ROMKEY
From: ROMKEY@XX.LCS.MIT.EDU (John Romkey)
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: Fast file transfer to PCs
Message-ID: <12379455706.53.ROMKEY@XX.LCS.MIT.EDU>
Date: 3 Mar 88 21:01:12 GMT
References: <2026@ho95e.ATT.COM>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 34

For fast transfers, the most important factors on PC's are the ethernet
interface, the processor speed and the disk speed, in order of importance.
Actually, the last two can be juggled around a lot; there's a wide variety
of processors (from 4.77MHz 8088's to 20MHz 386's) and disks (XT 8 bit hard
disk controller with 80ms disk to 1:1 interleave 16bit AT or 386 controller)
out there. So maybe the last two are of equal importance.

Anyway, if you don't want to write the data out to disk, then whatever you're
doing to dispose of it had better be able to fit into the amount of CPU
time and I/O bandwidth needed to achieve 1MB/sec if that's what you want.
You said lots of memory, so let's suppose the data just gets stuck in memory
and you'll do something with it when the transfer is over.

You probably want to use TCP instead of UDP. TCP has a reputation for being
slow with lots of overhead. I used to believe this myself, a long time ago,
and it is true in a poorly constructed TCP. But it's not necessarily
true of all TCP's. In order to get good performance, you need to have
several packets in transit at once and acknowledge them several at a time.
You can use an existing (hopefully well-written) TCP which will do all
this stuff for you, or you can build something on top of UDP which will
duplicate a lot of what a real TCP does. I'll go for using a good TCP
instead.

I've seen a real TCP transfer data at 1.6Mbits/sec between two 8MHz AT's,
memory to memory. No filesystem involved. This was with the best ethernet
interfaces on the market right now. I believe that if you increased the
speed of the AT's (putting a 386 in them would be nice) that the throughput
would still go up some - we haven't totally used up the AT bus yet. I think.

Yes, the dreaded Microchannel should improve things too, but this is in theory
and I've never seen any timings done on a PS/2 with a Microchannel ethernet
card. The Microchannel seems to be a faster bus, and network interfaces on it
should do 16 bit transfers instead of 8 bit, so things should run faster.
				- john
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