pc133 on a system with pc100 specs

[ucfswimmer]

im kinda confused...i know that the different varieties of ddr are merely indications of what their RATED speed is (for the moment anyways)...for example..pc2100 can do a 266mhz fsb, pc2400 can do a 300mhz fsb, pc2700 can do 333, etc etc...

i kind of assumed it was the same way with sdram...pc100 was rated for 100mhz speeds and pc133 was rated for 133 mhz speeds...well this led me to believe that if i had a computer with an older board that was maybe for example running a celeron at a 66mhz fsb speed and the memory at 100mhz, that i could put ANY pc133 mem in there and it would just downclock and run at pc100...i was told this wasn't so, so now im kind of curious as to what you guys think? does memory have to be exclusively advertised as running at 66/100/133 in order for you to know it'll downclock?

i was told that;

1) not all memory downclocks..."thats just the way it is"...is there a technical reason for this?

2) just because some pc133 downclocks on one board doesn't mean it will on another...so now it's up to the mobo and not the memory?

I'd like to be enlightened...and if necessary/possible let this person who i was talking to in on some info i receive...thanks a bunch

~jeff~

 

[ThePunkGeek]

no the ram will run at any speed under the tested speed aslong ad the motherboard support lower FSB (such as 66 are not common on newer boards)

 

[ucfswimmer]

*I* can take your word on it, but I don't suppose you have any way to cite your conclusion with some scholarly proof? (ie some official place that says just that?)

 

[ThePunkGeek]

not i will find some tho or you could always PM shadow or mother mods if they say you could that means 100% forsure

Good luck if i can find a site i shall post it

 

[ucfswimmer]

*bump*

anyone else have anything to contribute?

~jeff~

 

[Randy]

ufcswimmer, your thinking was correct. PC133 Ram is backwards compatible IE: if you put PC133 Ram in a system that was designed for PC100 the 133 will run at 100. I accumilated a few sticks of a 128 meg PC133 and am running it in an old Abit BE-6 slot one board with no probs, I'm also running a 128 meg stick in our Dell in shipping and receiving at work along with the orig. stick of 64 meg PC100
Randy

 

[Monaco]

it will work becasue PC133 is not just a name, it is a strict industry standard that manufacturers adhere to. It includes a whole bunch of specifications, one of which being a minumum operating speed.

anyways, the mem speed is controlled by a clock crystal on the motherboard itself- the RAM is essentially 'pushed' by the mobo to a certain speed. If you put PC133 in a PC100 system, it just 'pushes' the RAM a bit softer. Wish I could explain it better

I'll keep my eye out for the spec sheet, I don't have it on hand. I think it was from JEDEC, but I can't remember.

 

[David]

My dad runs 64MB PC100 and 64MB PC133 in his rig - FSB is 83.3MHz. Runs fine. I can change my BIOS settings to run my PC133 at PC100.

 

[DDR-PIII]

I can change my BIOS settings to run my PC133 at PC100.

Why would you want to do that ?

 

[ucfswimmer]

well this helps...but i still need something..thanks for all your responses..any info on where i can get JEDEC standards at?

~jeff~

 

[David]

Why would you want to do that ?

Proof that PC133 will run at PC100 spec. I always run it at PC133 of course.

 

[Gnufsh]

I've never had any problems running at less than rated speed. I believe the standard is supposed to be backwards-compatible...

 

[Monaco]

found this on Google:

http://www.via.com.tw/news/pc133develop.htm

hope you like engineering diagrams!

a few quick searches ought to find you plenty more just like it. I couldn't find the JEDEC homepage for some reason...