Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!zaphod.mps.ohio-state.edu!mips!pacbell.com!pacbell!att!dptg!pegasus!dmt
From: dmt@pegasus.ATT.COM (Dave Tutelman)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Passing  GO, etc. (was Re: OEM)
Message-ID: <5003@pegasus.ATT.COM>
Date: 25 Aug 90 14:57:07 GMT
References: <4973@pegasus.ATT.COM> <DR2eo2w162w@cybrspc>
Reply-To: dmt@pegasus.ATT.COM (Dave Tutelman)
Organization: AT&T Bell Labs - Lincroft, NJ
Lines: 37

In article <DR2eo2w162w@cybrspc> cybrspc!roy@cs.umn.edu (Roy M. Silvernail) writes:
>dmt@pegasus.ATT.COM (Dave Tutelman) writes:
>
>> [ Hint to the semi-aware.  The modem's
>> baud rate can be either higher or lower than the bits-per-second at
>> which you transfer data.  Offhand, I can't think of a single modem
>> where it's the same. ]
>
>I can.... a 300-baud modem.

Sorry, Roy.  That's one where the bit rate is lower than the baud rate.
(See my posting of this morning.)  You can't send 300 bits per second
over a 300 baud modem, because there's no clock signal at the modem's
RS232 interface.  Consequently, you must "waste" some of the binary
transitions on non-information carrying synchronization.  The usual
(but not the only) way of doing this is the insertion of start and
stop pulses, one of each per 8 information bits.  This cuts the
bit rate of a 300 baud modem to 240 bits per second.

>(of course, that's ancient history. nobody really uses 300-baud anymore,
>do they? ;-)

Thanks, I needed that  ;-(   I was in the data communications business
when 110 baud was "the new thing", 150 baud transmission was available
but terminals were too slow to use it, and 300 baud wasn't even on
the shelf.  (That snapshot dates to 1962.)  In the 60s and 70s, one of
my specialties was the information content and bandwidth requirements
of bit-stream (and byte-stream) synchronization, so I'm particularly
sensitive to this issue.

Dave
+---------------------------------------------------------------+
|    Dave Tutelman						|
|    Physical - AT&T Bell Labs  -  Lincroft, NJ			|
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