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Xref: sserve comp.os.linux.development:19690 comp.os.linux.misc:30178 comp.os.386bsd.questions:14586 comp.os.386bsd.misc:4157 sci.electronics:84649 Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!msuinfo!uwm.edu!math.ohio-state.edu!news.acns.nwu.edu!ahab.eecs.nwu.edu!hpa From: hpa@ahab.eecs.nwu.edu (H. Peter Anvin) Newsgroups: comp.os.linux.development,comp.os.linux.misc,comp.os.386bsd.questions,comp.os.386bsd.misc,sci.electronics Subject: Re: 16550 detection Date: 21 Nov 1994 03:49:40 GMT Organization: The United Federation of Planets Lines: 38 Message-ID: <hpa.1e210000.Allah.u.Abha@ahab.eecs.nwu.edu> References: <CMETZ.94Oct30051603@itchy.inner.net> <JKH.94Nov2210122@freefall.cdrom.com> <Cyp34w.MxC@bonkers.taronga.com> <3a8u29$mi@awfulhak.demon.co.uk> Reply-To: hpa@nwu.edu (H. Peter Anvin) NNTP-Posting-Host: ahab.eecs.nwu.edu Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-PGP-Key-Available: finger hpa@ahab.eecs.nwu.edu Followup to: <3a8u29$mi@awfulhak.demon.co.uk> By author: brian@awfulhak.demon.co.uk (Brian Somers) In newsgroup: comp.os.linux.development > > What was the bit in the middle ? Where do the 2-6 bits on each of > 512 channels come from ? > That wasn't what it said, you got confused (which is OK, this is pretty technical and quite frankly of little relevance to you as a modem *user*). > Please inform someone who thought that bps was the same as baud of > their ignorance.... Okay: baud is bits per second *PER ONE-BIT CHANNEL*. V.32bis modems, for example, are 14400 bps and 2400 baud. This means that 2400 times a second, six bits are transferred (six one-bit channels). These six bits are transferred SIMULTANEOUSLY. Think of it as a track with runners, where each runner starts when the starter's pistol blows. If you want 14400 runners to start a second, you can either have one runner start each time and fire the gun 14400 times a second, or you can have six runners start every time you fire the gun and fire it 2400 times a second: 2400 x 6 = 14400. This distinction is important for several reasons, but for a modem user it is easiest just to forget about baud and talk about bps. The ultimate example of disparity between baud and bps is the TeleBit Trailblazer modem (PEP) which uses up to 512 channels, each carrying up to four bits, for a total of 2048 one-bit channels. The Trailblazer operates at a little over 7 baud, but was still for a long time the fastest modem you could get your hands on, since the total capacity was over 2048 channels x 7 baud = 14336 bps (it was about 16000 or so if I remember it correctly).