Core memory emulator using non volatile ram.

ED SHARPE couryhouse at
Sun Dec 16 10:36:54 CST 2018

Anyone building  8 omnibus  batter  backed up core  replacement  currently  that  is  available off the  shelf reasonably for   8 m,e and  f? (( Smaller  size  board  than the   8a   would accept   for memory as I  remember..))

Have  a 8 m or  f  in my  den on a  shelf...   as  as I  best  remember  it  20  years ago  had  4 k or   flaky  core in it.  might  be  fun  to play  with. 
Alas  there  might  me other things  wrong on other boards  by now  too....
In a message dated 12/16/2018 6:44:55 AM US Mountain Standard Time, cctalk at writes:

On 12/15/2018 01:01 PM, Guy Sotomayor Jr via cctech wrote:

> FRAM or MRAM. I make extensive use of them in my projects.
> Everspin has a few (all SMT and 3.3v). As I recall they run ~$20/ea for 4Mb (512K x 8 or 256K x 16).
> TTFN - Guy
>> On Dec 15, 2018, at 1:22 AM, Rod G8DGR via cctalk <cctalk at> wrote:
>> I have an idea to produce an MM-8 clone using RAM that acts like core when turned off.
>> Can anybody suggest a chip that will do this?
>> Rod Smallwood
My call on this is that cmos static ram 4Bit wide does the job well I
have 32K of it in my PDP-8 to
get past possible failure of hard to find and get core.  A Panasonic
BR-1 lithium cell has enough
capacity at the measured drain for about 6-7 years and the Dallas power
management chip
makes it a non hack.  Flash, EEprom and Magnetic FRAM and MRAM) types
have many unacceptable
properties for a random access read write memory.  It makes no
difference to the PDP8(ILEFMA)
that read is not destructive as it will write back as needed anyway.

There is a design on the 'net for using CMOS ram in a straight forward
buildable array for Omnibus
with battery back up that is fine.  Don;t get wraped around the axle
about RMW as any sufficiently
fast ram can do that without wearout.  And compared to core it doesn't
take much speed.

EEprom and Flash work fine for read mostly disks or disk simulators.


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