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From: jallen@csserv2.ic.sunysb.edu (Joseph Allen)
Newsgroups: comp.arch
Subject: Re: Memory speed, why so slow?
Message-ID: <1991May17.205527.7125@sbcs.sunysb.edu>
Date: 17 May 91 20:55:27 GMT
References: <9245@idunno.Princeton.EDU> <RAJE.91May9115209@lattice.stanford.edu>
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In article <RAJE.91May9115209@lattice.stanford.edu> raje@lattice.stanford.edu (Prasad Raje) writes:
>In article <9245@idunno.Princeton.EDU> ssr@stokes.Princeton.EDU (Steve S. Roy)
>asks:
>The cell size must get smaller, but the cell capacitance cannot.
>Why? 
>You need a large enough cell capacitance to guard against soft errors due
>to radiation. That is you need to store at some minimum number of electrons
>per cell. These days this number is in the few tens of thousands of electrons.
>The second reason you need a certain minimum charge is to be able to drive
>enough of charge onto the bit line. The cell state is sensed by charge sharing
>between the dinky cell capacitance (~ 50 fF) and the huge bit line capacitance
>( ~ 1 pF). 

Why is this a problem?  Just have more sense amplifiers.  Or equivelently,
break the dram into small banks (I believe this is done).

Also I don't know the exact numbers to calculate it, so which is better:

	Big cells which don't error

	Small cells with enough excess so that you can error correct (during
	refresh perhaps)

Hmm that reminds me:

I once worked for a company which made character generators for those stupid
cable channels.  One of the machines used CCD memory.  CCD memory is very
sensitive to alpha particles I think.  Anyway, it made mistakes so often that
the user had to look through the text every once in a while to fix things.  Of
course, no one ever reads those channels so it doesn't really matter.  

-- 
/*  jallen@ic.sunysb.edu  */     /* Amazing */     /* Joe Allen 129.49.12.74 */
int a[1817];main(z,p,q,r){for(p=80;q+p-80;p-=2*a[p])for(z=9;z--;)q=3&(r=time(0)
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]?a[p+=a[p+=q]=q]=q:0:0;for(;q++-1817;)printf(q%79?"%c":"%c\n"," #"[!a[q-1]]);}