Date: Sun, 14 Jul 1996 01:20:11 -0400 From: "Jacob M. Parnas" <jparnas@jparnas.cybercom.net> To: Henry Spencer <henry@zoo.toronto.edu> Cc: hardware@freebsd.org, bsdi-users@bsdi.com Subject: Re: cable vs. ISDN Message-ID: <199607140520.BAA00558@jparnas.cybercom.net> In-Reply-To: Your message of Sat, 13 Jul 1996 22:19:01 EDT. <Pine.3.89.9607132250.A239-0100000@zoo.toronto.edu>
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In message <Pine.3.89.9607132250.A239-0100000@zoo.toronto.edu>you write: >> ...Modems seem to have like a 2-4 Kbyte FIFO, even >> inexpensive ones, made back in the mid 80's. Why, except for poor design, >> weren't they at least an option on the computer side. (1 byte was normal, 16 >> was "buffered") > >The modems weren't single-chip devices. They were a boardful of >electronics, typically including at least one microprocessor. (At one >point, the modem I was using had considerably more computing power than >the computer it was connected to.) In fact there was no actual FIFO on >them -- the microprocessor had a few KB of RAM, and used that for data >buffering among other things. Its weird that sufficient buffering was available on the modems (though it took more boardspace possibly. I doubt it would in todays technology). Yet only 1 byte (or up to 16 was available on buffered boards. >> I'm also confused as to why building FIFO's is difficult or complicated. >> I remember we built one as a project in my first hardware course back in >> 1982-1983 and nobody found it hard (it was a beginning minor project nobody >> seemed to have problems with. > >It's easy enough to do, but doing it on a chip does eat a fair bit of space. I've looked at circuit boards of that time and the space was definately available, especially on 4 port-16 port boards. >> >Only when you start running a real operating system (or a kludged imitation >> >thereof :-)) do you start to care about buffering. >> >> True, but even machines like Sun Sparc 2's or IBM RT's which only ran Unix >> had small FIFO's. And they only ran Unix. > >However, if you look inside them you will usually find that their serial-I/O >chips are off-the-shelf commercial designs built for other markets. > > Henry Spencer > henry@zoo.toronto.edu I did and your're correct. But why when both had extra space on them? Well, I guess hindsight is 20/20. *sigh* Thanks for the information. Sincerely, Jacob
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