PDP-8 /e/f/m memory

Don THX1138 at dakotacom.net
Tue Aug 15 11:33:25 CDT 2006

Allison wrote:
>> Subject: Re: PDP-8 /e/f/m memory
>>   From: Don <THX1138 at dakotacom.net>
>>   Date: Mon, 14 Aug 2006 20:50:25 -0700
>>     To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
>> Chuck Guzis wrote:
>>> On 8/14/2006 at 7:25 PM Bob Rosenbloom wrote:
>>>> How about two Ramtron FM18L08's? Nonvolatile like core with no battery 
>>>> to die or leak. Would need level shifters to 3.3 volts
>>>> and slightly different timing. Low power, and in DIP or SMT. I'm just 
>>>> tired of cleaning boards that had batteries that leaked all over them.
>>> How long will a supercap keep that much SRAM alive?
>> Why not use a *big* battery/cell... aren't we talking
>> about a design that would end up WAY undersized?  Even
>> scaled would leave lots of real estate that you could
>> install a conventional AA, 9V, etc. battery and forget
>> about it "forever"
> Because most batteries have shelf life!  The average battery dies in 
> a few years from just sitting.  The LI cells are designed for very long life.
> I have a few sub-C sized LI cells that are over 15 years old and going strong.

The shelf life (self discharge rate) of most batteries is *MANY*
YEARS.  The AAA cells I bought last year for my Visor have a
"expiration date" of 2013.

A low power BBRAM design essentially falls below this self
discharge rate (unless you get sloppy with the design).
The real problem is ensuring that the batteries (i.e. the
equipment that they are stored in) doesn't sit in
temperature extremes, high humidity, etc.

And, if you're storing your '8 in those conditions, I suspect
one of these days you'll be in for an unhappy surprise as
you "suddenly" discover components that have fatigued

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