PC100 memory on PC66 bus

[_Nauht_]

I've tried installing a stick of 128MB of PC100 RAM to replace a stick of 32MB of PC66 RAM on an IBM P2-300 computer (6561-53U). Right after POST, the computer freezes and I checked IBM's WWW and it says that this computer only takes PC66. Even so, shouldn't PC100 memory work on a PC66 bus? Or do I have to have strictly PC66? Thanks.

 

[skriefal]

The RAM speed (PC100 vs PC66) almost certainly has nothing to do with why the PC100 stick doesn't work. It may, however, be due to how the DRAM chips are organized into banks on the PC100 stick, or because the PC100 stick is using DRAM chips that are too dense and cannot be recognized by the memory controller.

Older SDRAM sticks will be more likely to work since they'll probably use less dense DRAM chips, so you'll have better luck if you can find an old PC66 stick.

 

[_Nauht_]

When you say "density," do you mean how much can each chip on the stick hold?

 

[Iron Woode]

PC100 ram just will not work in a PC66 spec system.

PC66 ram can still be bought, but is expensive now. You can try E*bay.

 

[skriefal]

Iron Woode... what you're saying is sometimes true, but is certainly not always true. I've used PC100 and even PC133 SDRAM sticks in systems meant to use PC66, with no ill effects.

It's possible that PC100 SDRAM sticks won't work in a PC66 system, but if so then the simple PC100 vs PC66 speed difference is not the cause of the incompatibility.

 

[RickH]

I have used PC 100 memory in LX chipset MBs at 66 MHz. The PC 100 would not work in a old VX chipset pentium MB that can use SIMMs or DIMMs at 66 MHz. R.

 

[_Nauht_]

Thanks for all your help guys. I've asked a friend, who is a tech at a computer store, and he also said that PC100 won't work on a PC66 system. I'm gonna try and exchange PC100 for PC66.

 

[Regalk]

What should be said is this:
On PROPRIETARY systems (HP, IBM, Q) using PC100 (generic) MAY not work on PC66 bus. ON OEM systems (Dell, and custom built) even PC133 will work on PC66 bus. My brother has 128mb PC100 on his Soyo LX board and I have a little Internet server with PC100 on an ASUS TXP4 board. Never listen to store personnel cause if youdo NEVER say that on these forums otherwise you will get creamed.

 

[holdencommodore]

I thought that most ram was backwards compatible?

 

[Sukhoi]

It should work. I'm running a Celeron 433 on an i440LX motherboard. I have one 128 MB PC100 DIMM, and one 64 MB PC100 DIMM. In SiSoft Sandra the 64 MB DIMM is actually recognized as PC133. All of my RAM works fine. 🙂 The PC rating for RAM is just the speed, so theoretically PC133 should work fine in PC66 motherboards. I know this isn't always true though.

 

[_Nauht_]

*bump*

 

[_Nauht_]

*bump*

 

[RickH]

Have you tried other memory?? Borrow some from another machine. If there is a Best Buy in the area purchase a SIMM an try that. If it doesn't work they will take it back. Before you buy from other sources check their return policy. I have used PC 100 memory in place of PC66 on several boards, but it would not work on a HX chipset pentium board. R.

 

[_Nauht_]

What I'm gonna do is just get PC66 sticks made by IBM... that should definately work. If not, IBM is just screwed.

 

[Spocko]

I've got a Tyan S1570-AT (430TX) board that takes 66MHz DIMMS. I'm running 256Mb of Crucial PC133 in it, and it works great.