Path: utzoo!mnetor!uunet!oddjob!ncar!ames!pasteur!ucbvax!unisoft!gethen!farren
From: farren@gethen.UUCP (Michael J. Farren)
Newsgroups: comp.arch
Subject: Re: RAM Question:
Message-ID: <888@gethen.UUCP>
Date: 22 Apr 88 06:04:52 GMT
References: <1005@iitmax.UUCP> <1988Apr20.195805.25922@gpu.utcs.toronto.edu>
Reply-To: farren@gethen.UUCP (Michael J. Farren)
Distribution: comp.arch
Organization: There's Unix there in Oakland
Lines: 32

sarathy@gpu.utcs.UUCP (Rajiv Sarathy) writes:
>
>In article <1005@iitmax.UUCP> cs450edf@iitmax.UUCP (edward federmeyer) writes:
>>"0 Wait State" and "1 Wait State".  What do they mean by these terms? ...
>
>A 'wait state' is the number of clock cycles that a computer must wait before
>proceeding with the next instruction.
>
>While waiting, the computer refreshes RAM.

Close, but no cigar.  If the access time of a memory system (the time
it takes for valid data to appear at the outputs after a valid address
has been presented to the inputs) is longer than the time which the
processor requires the data to be present, the processor has to wait,
with its memory circuits idle, until the data are there.  A wait state
is simply a measure of that time, usually a multiple of the clock
speed.  If, for example, your memory takes 500 nanoseconds to produce
valid data, but the processor, running at 10 MHz, expects the data
to be present after 400 nanoseconds, the processor will wait one clock
cycle (100 ns), and so that particular memory will impose one wait state.

During this time, memory is typically NOT being refreshed - it's busy,
it can't be bothered with that refresh stuff.  Refresh takes place
as a seperate operation (although snazzily designed memory systems
can make this process nearly invisible to the processor), and usually
requires most of an entire memory cycle.

-- 
Michael J. Farren             | "INVESTIGATE your point of view, don't just 
{ucbvax, uunet, hoptoad}!     | dogmatize it!  Reflect on it and re-evaluate
        unisoft!gethen!farren | it.  You may want to change your mind someday."
gethen!farren@lll-winken.llnl.gov ----- Tom Reingold, from alt.flame