PC133cas3<>PC100cas2...?

[Rigoletto]

My new memory module finally arrived but my 100 bus board automatically sets the CAS at 3. Manually rectifying it rendered windows 2000 unable to boot. And I was getting faults in ME too, blue screens all over the place, persisting even on CAS3. Ugh.
I have to send this memory back obviously. But I just thought I'd warn you that if you had a fussy motherboard or bought generic PC133, you might not be able to run it at 100cas2, folks...
I don't believe I damaged the memory because I had to swap my DIMMs around and I would have knackered the others at the same time if I had. But BIOS reports the new RAM as OK thought practice most definitely does not. I would have run CheckIT but couldn't get it to work correctly today.
Does anybody know how the memory will be tested on RMA? If they test it like I did, the memory should fail. If they put it through a motherboard boot, then it will pass and I will have to pay a restocking fee.
Also can anyone direct me to reference quoting performance advantage of CAS2? THX

 

[Dfuse]

Can anyone tell me the difference between CAS 3 and CAS 2!?!
Also is SIMM better or DIMM. I am planning to buy some extra memory and I just don't know the difference between these different types!

cheers.

 

[Noriaki]

CAS is one particular timing value and it's a latency (measured in cycles) so lower is better.

You want 2-2-2 rated RAM. CAS2 is usually 2-2-2 but you could have 2-3-3 and it woudl still technically be CAS2, but not as good as 2-2-2.

Rigoletto:
133Mhz frequency gives you a 7.5ns cycle time (yes PC133 is often rated 7ns, but frequecy and period are inverses, 133Mhz = 7.5ns, the 7 just gives you some breathing room). CAS3 is 3 cycles so that's 22.5ns CAS active time...
100Mhz frequnecy gives you a 10ns cycle time (see above replace 7 with 8 and 7.5 with 10). CAS2 is 2 cycles so that's 20ns CAS active time.

So technically when you run PC133 CAS3 @ PC100 CAS2 you are asking it to shave more than 10% off the CAS active time. That could cause problems.
If your PC133 is rated at 7ns, 3 cycles then is 21ns, so CAS2 PC100 is only about 5% less...but still the timings on PC100 CAS2 is a bit quicker than PC133 CAS3. (PC133 CAS3 has better performance, as we've seen in the past, I'm not talking performance here, just time)

I'm sure there is plenty of PC133 CAS3 that will do PC100 CAS2, but from a strict analysis it's not guaranteed.

 

[smukkel]

If you use search you'll find a lot of threads on this topic.

 

[Rigoletto]

I have not bothered to put that memory back in my PC, I am getting an RMA even if I lose 25% on the deal for a refund.

Thankyou Noriaki.
No thankyou snukkel, I did not find much of information in the search. In fact I found MISinformation instead. I repeat that generic 133cl3 does not perform like pc100cl2.