Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!uunet!lll-winken!taurus!cs!schweige
From: schweige@cs.nps.navy.mil (Jeffrey M. Schweiger)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Baud vs. bps.
Message-ID: <1308@cs.nps.navy.mil>
Date: 25 Aug 90 02:09:43 GMT
References: <849@idcapd.idca.tds.philips.nl>
Reply-To: schweige@cs.nps.navy.mil (Jeffrey M. Schweiger)
Organization: Naval Postgraduate School, Monterey CA
Lines: 37

In article <849@idcapd.idca.tds.philips.nl> lexw@idca.tds.PHILIPS.nl (Lex Wassenberg) writes:
>
>Okay, in some recent articles there were these hints about the difference
>between "baud" and "bits per second". Now I for one have always thought that
>baud and bps is the same. So what's the difference? Has it something to do
>with bits that don't carry actual data like start and stop bits? Or is it
>more subtle? Thanks to anyone who can inform me (and others).

The term 'baud' represents the number of times per second that a signal changes
its value or state (for example, voltage level or frequency), the baud number 
itself is frequently referred to as the 'baud rate', and has units of 
measurement of inverse seconds.  As Hertz (Hz) also has units of measurement of
inverse seconds, an estimate fot the maximum baud rate of a channel is its 
bandwidth.

Baud rate is not immediately useful as it actually represents how fast the
signal modulation changes.  Usually a data communication user is more
interested in the actual speed of data transfer.  Therefore, the measure of
how many 'bits-per-second' (bps) is more useful in determining how hast data is
transmitted.  Baud and bps are related by how many bits are transmitted in one
signal change.  For low speed modems, such as the 300 bps modems following the
Bell 103 or CCITT V.21, the baud rate and the bps are the same.  With higher
speed modems, the modem protocols used transmit more than 1 bit per signal
change, and the bps will be greater than the baud rate.  For example, 2400 bps
modems following the CCITT V.22bis protocol are actually 600 baud modems as
they transmit 4 bits per baud using a technique known as Quadrature Amplitude
Modulation (QAM).

Hope this helps.

Jeff Schweiger

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