RAM Speed

[Super-Slasher]

Okay, I'm a bit confused as exactly what type of RAM I need, I'll try to explain it the best I can...

My IBM PC AT's on-board RAM (512KB) consists of memory chips that operate at a speed of 150ns. My extended memory board which takes 30-pin SIMM's has no specifications of RAM speed (that I know of) and I do not know the speed of the current 2, 1MB sticks of RAM that are in there.

I am going to be getting 12, 256K sticks of RAM to put the extended memory board to it's maximum of 3MB that come in many varieties of speeds from 100ns to 60ns. The only kind that is availble to me in 12 matching sticks is 80ns.

Would this work in my system? I have absolutely no idea how RAM-timings work in systems. I'm pretty sure that there's no problems if you use RAM that is faster than your system normally writes (for instance in my regular computer I have 2 sticks of PC133 RAM when my system is 66FSB), the only problem is if you use RAM that's slower than your system writes.

Just want to make sure... thanks.

 

[mbbrutman]

Slasher,

It's easy. And I like you because you're an AT guy, so I'll give you the keys ...

The clock speed of a normal AT is either 6 or 8 Mhz, depending on which version it was. Let's assume a fast AT running at 8Mhz. That's 8 million cycles per second, or a cycle time of 125ns.

The memory chips on the motherboard are 150ns. The 150 is 'access' time, or the time it takes to make an initial read to the chip. The AT has a 'cycle' time of 275ns, which is quite a bit more. Cycle time is the time it takes to do back-to-back reads. For example, to do two back to back reads you have to first access the chip, which takes 150ns. Then it takes another 125ns to warm the chip back up again so that it's ready for the second read. (And hence a cycle time of 275ns.)

80ns memory will be fine - by quite a wide margin too. Don't worry about it.