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Mixing RAM speeds

In these older systems, I believe the rule is that the CPU needs RAM that can respond within a certain rating (a little bit different than these days with variable memory clocks and autodetection etc.); I don't know where you might find the rating required here, but if we are to assume that the CPU needs 100ns memory, you must provide 100ns or better; as long as it's the same type, the speed shouldn't matter...

"The amount of time that RAM takes to write data or to read it once the request has been received from the processor is called the access time. ... Although fewer nanoseconds is better, user-perceived performance is based on coordinating access times with the computer's clock cycles. Access time consists of latency and transfer time. Latency is the time to coordinate signal timing and refresh data after reading it."
 
If the 120nsec DRAM isn't costing you and you have excess chips, try using it and shaking it out with some good RAM diagnostics.

You'll probably find that 120nsec parts will work just fine.
 
120ns memory is good for 8MHz operation with 0ws.
100ns memory is good for 10MHz operation with 0ws.

I don't know too much about memory ratings with added waitstates, but I believe with 1ws you should be able to go to at least the next speed grade. For example, I think 120ns memory would work at 10MHz with 1ws. See if your board supports waitstates either through jumper or BIOS settings.

Also, some memory may work faster than rated. It doesn't hurt to try.
 
Is this DIP RAM or SIMM RAM that you are referring to?

If it's SIMM RAM it's a buck a stick if even that much at most flea markets for 30 pin stuff, when you can find it.

For DIP RAM, post what you have in it by part #. Several of us have spare chip stock and I also sell that stuff on my website. Maybe we can do a swap out on chips.

RJ
 
DRAM of the early-mid 1980's era varied widely in terms of characteristics. Generally speaking, if you've got Japanese DRAM, you're better off with the US-designed stuff, at least according to my own experience.

Remember that DRAM labeled 120nsec is guaranteed for that speed and may, in fact, surpass it by quite a bit, if you're willing to select the better parts.
 
I finally managed to find some DRAM. They seem a little bow-legged, and won't fit in their sockets. I'm not sure if the chips are supposed to be like that, or if the tubes they were shipped in bent the pins. Is there some special method or tool required to install them?
 
Do you mean you can't install them because the pins bend when you try or that the pins aren't the right distance because they're bent a bit? I read it as the latter but I've never done anything more than take pliers and bend the legs like I need them. Again, that's assuming they're good and strong so they don't do anything dumb when installing them.

Not sure if there's a professional way but it's worked for me.
 
If it's a new DIP with bent-outward pins, I simply hold the IC so that the pins on one side and then the other are flat against a table top, and then manipulate the IC body itself so that the pins are bent to an exact right angle. No tools whatsoever used.

On the other hand, if the pins are really bent from mishandling, a pair of smooth-jawed long-nose pliers can bring them to rights. Don't use serrated-jaw pliers; you'll damage the pins.

There are things called DIP Insertion Tools, but I've never felt the need.
 
54 chips later and I think I may have screwed a couple up. I get the error:

01664 KB OK

200000 0000 201-Memory Error
164-Memory Size Error

I installed 2.125MB. Does this indicate an entire bank as malfunctioning, or does it help identify which specific chip is in disorder (as in, the memory check stopped at the bad one)?

I mangled the pins on one chip, though I managed to straighten them out, and the last bank has memory from four different manufacturers, as that's what the dealer shipped to me. I'm guessing one of the two is the problem, thought I may have bent the pins on another chip without noticing.
 
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