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Path: utzoo!utgpu!lharris
From: lharris@gpu.utcs.utoronto.ca (Leonard Harris)
Date: Sat, 26-Aug-89 19:55:11 EDT
Message-ID: <1989Aug26.195511.16016@gpu.utcs.utoronto.ca>
Organization: University of Toronto Computing Services
Newsgroups: comp.sys.atari.st
Subject: Re: 1040ST Memory Upgrades
References: <1233@cs.rit.edu> <1089@ultb.UUCP> <974@psc90.UUCP> <1143@ultb.UUCP>
Reply-To: lharris@gpu.utcs.UUCP (Leonard Harris)
Distribution: usa

In article <1143@ultb.UUCP> clf3678@ultb.isc.rit.edu.UUCP (C.L. Freemesser) writes:
>>>I really don't suggest you get a memory upgrade for the 1040st.  
>>[very general reason why not]
>>Could you be more specific ??
>
>Sure I can.  The power supply in the 1040ST was only meant to supply
>power for 1 meg of chips.  Of course, there is a little extra output in
>the supply (a safety margin of sorts).  But since nothing is perfect,
>and we live in a non-perfect world, not every power supply in every 1040
>has the same output.  Some have more, some have less, some have the
>intended output.  Ergo, a memory upgrade MAY OR MAY NOT strain your
>power supply.  If Atari had given us a LARGE safety margin, then
>probably every 1040 could be upgraded.  From what I know of the 1040,
>a 2.5 meg upgrade should be ok.  However, your power supply may not be
>able to handle a 4 meg upgrade.  This is why I discourage upgrading the
>1040 to more RAM.  You just don't know if it will work or not.
>
... lots deleted about PC power supplies ....


I really get annoyed when people who know very little, give very authoratative
advice on the net.
First - I am writing this on a 4 meg, 16 mhz atari 520ST. - it works!

Now about memory upgrades using too much power - the power supply puts
out roughly 3 Amps.  Thats quite a bit.
256K rams use about 350mW per chip when active and 20mW per chip
when in standby (not accessed by RAS or CAS) these are NMOS devices and
therefore use a lot of power.
1 megabyte rams use between 70 and 120 mW when active and 10uW when deselected.
1 meg rams are variations of CMOS and use relatively little power.

Thus: 1 megabyte of 256K ram = 32 chips x 350mW = 11.2 W of power (if all chips
were active at the same time which could never happen).  If the typical case 
where 1 chip was selected and the others in standby the power would be 
1x350mW + 31x20mW = 970mW.

4 megabytes of 1 meg rams = 32 chips x 100mw = 3.2 W.  the real world power
would be 1x100mw + 31x10uW = 100.31 mW.

So, upgrading your atari to 4 megabyte of ram will actually save 9 times as
much power form you power supply.
Sorry to post this but this was the third message from this guy on the same
subject and it started to get on my nerves.
/leonard