Memory/cache on the 11/70

Dave McGuire mcguire at
Fri Jan 9 15:03:34 CST 2009

On Jan 9, 2009, at 3:55 PM, Ethan Dicks wrote:
>>  Standard chips good.  Weird chips from the PC world, bad.
> I'm not advocating the reuse of SMT 128K cache chips, but the 32Kx8
> DIP chips from old motherboards have a JEDEC-compatible pinout (they
> might designate various data or address bits in a different order, but
> for RAM it's irrelevant), and are only 0.3" wide (meaning you can use
> two 14-pin sockets rather than having to buy yet another footprint).

   Hence, they're not "weird chips". =)  It's the weird ones I'm  
worried about.

> I've seen more than one hobby design that had a 0.6" footprint for a
> 62256 _and_ narrow pads for a 0.3"-cache SRAM (and even with SMT pads
> inside that).  It's possible to be flexible for no significant extra
> effort.

   That's very nice indeed.

> The DIP cache SRAMs are no longer cheap-as-chips, but some of us have
> a tube or two stashed away and I sure don't mind using them for
> non-battery-powered circuits.

   The JEDEC ones, or the "weird" ones?  I see some from time to  
time, and I grab them if they're "standard" enough.  I got a pair of  
really 20ns nice cache SRAMs on eBay last year, Paradigm  
PDM41256SAs.  Despite their seemingly familiar part number, they are  
32kx8 SRAMs, not 256kx1 DRAMs.  They're in 0.3" ceramic 24-pin DIPs.   
I'm saving them for a "pretty" Z80 SBC that I'll be building soon, on  
which all chips are ceramic.  (I've always had a great love for  
ceramic chip packages, and I grab useful ceramic-packed chips  
whenever I can)


Dave McGuire
Port Charlotte, FL

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