Single buffered Ethernet adapters Was: OS/2 Warp, was Re: PCjr Telnet Server
ethan.dicks at usap.gov
Mon Sep 22 03:56:04 CDT 2008
On Sun, Sep 21, 2008 at 08:39:31PM -0400, Dave Mitton wrote:
> On 9/18/2008 01:04 PM, cctech-request at classiccmp.org wrote:
> >From: Paul Koning <Paul_Koning at Dell.com>
> >>>>>> "Ethan" == Ethan Dicks <ethan.dicks at usap.gov> writes:
> > Ethan> Back when NIC weren't $10 each, I remember the easiest to work
> > Ethan> with (in terms of compatibility) were the NE2000 and clones
> > Ethan> (NE1000 for 8-bit machines), the WD (later SMC) 8013, and the
> > Ethan> 3C501, later displaced by the 3C509. ...
> >Something to keep in mind is that the 3C501 is an extremely bad
> >design. It is completely incapable of dealing with back to back
> >packets -- even just two of them. And of course that's a perfectly
> >normal situation in any plausible network.
> >I remember working on DECnet when these toys came around, and the
> >request came in to have a "go slow" feature in DECnet to support this
> >single buffered design. The answer, of course, was "NFW". (Slowing
> >down at the source wouldn't have helped because the network could
> >easily cause clumping anyway...)
> > paul
> The problem with the 3C501 (and the InterLAN and Ungermann-Bass, and
> other I've forgotten about) Ethernet cards of this era where that
> they only had one packet of memory on them.
This sounds familiar, but not in terms of ISA NICs... ISTR some
sort of similar issue with the DEQNA. Some of my friends in the
Ohio State University CIS program "enhanced" some networking code
on one or more of the UNIX servers in their group to the point
that it could slam out 2-3 back-to-back packets before going back
to gulp up more data to transmit. The problem was that someone
else in the group had a MicroVAX that would reliably crash when
this happened. IIRC, it was determined that the DEQNA couldn't
juggle a received packet while a new one was coming in. I can't
confirm that it's a single-buffered issue, but it sounds like it
fits the symptoms.
In the end, they had to rip out some if not all of their
enhancements because equipment of the mid-1980s was expecting
all the hosts to be so slow that there would always be time
to deal with one packet before the next came in.
Obviously later, things changed, but in 1986 or 1987, that
wasn't a fatal assumption.
> NetWare and NetBEUI driven networks hardly noticed this problem for
> two reasons: 1) they were Request/Response protocols. They normally
> did not expect additional packets until they responded, and 2) they
> were talking to other PCs. Which simply couldn't generate traffic fast
Exactly. The same was true for small VAXen, from what I saw.
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