Is PC133 SDRAM backwards comaptible?

  Dumfy 14:31 14 Aug 2003

Hi all,

Back again. This follows on from an earlier thread of mine.. click here

Is PC133 SDRAM backwards compatible with PC100 SDRAM, that is, will PC133 run at the slower speed of PC100?

The motherboard has only two slots available for memory. I purchased a single stick of 256MB PC133 as the shop didn?t have any at PC100. My intention was to add this to the 64MB PC100 already in there.

However, the PC won?t boot with the 256MB stick in at all ? either alone or in either of the available slots, or together with the 64MB stick. It?ll only boot with just the 64MB in place. Can?t access the BIOS either.

I assume a couple of things. Either it isn?t compatible or the 256MB stick is faulty (branded memory). The shop has already said I can return it if I have problems which is good.

I?m now thinking of either leaving out the 64MB stick and putting in 2 of 128MB PC100, or a single stick of 128MB with the original 64MB. Is 192MB enough for Windows XP to run on?



  [DELETED] 15:20 14 Aug 2003

PC133 memory should work ok with your system though will only run at FSB speed of your moby, probably 100 in your case. My memory is 128mb pc100 (original) and 256mb pc133 - - - only bought the pc133 as couldn't get the pc100 at that time, maybe 2 years ago.
Would get this new studd checked out - - -you should be able to use a stick of 256.
Someone told me, when I wopped my extra stuff in there, that the biggest stick should be in slot 1 - -so I took 128mb out of 1, stuck the 256 in that slot then 128mb into slot 2. I have since read somewhere that this doesn't make any difference. Just my 2 penneth.

  [DELETED] 15:46 14 Aug 2003

They may be two reasons why the ram is not working.

The FSB of the 667 celeron is here
Installing Pc100 ram is usually alright. What you are trying to do is to cut the speed down to half, from 133Mhz down to 66Mhz.Do try to get into the bios to see if you can increase the fsb of the ram.

The other thing is that some boards, especially older ones running at 66Mhz, have a limitation to the amount of ram that a slot will take. Some are 64Mb, some 128Mb and some 256Mb. A look in the manual, if they have one, will tell you the memory limits of the slots.

  Dumfy 19:56 14 Aug 2003

I see what you're saying bsod. There is a stickers on the front of the case from the manufacturer that states 256MB is the max. That's what I thought the problem was when I had 320MB in there, but as I say, it still failed to boot with the single stick of 256MB.

It boots fine with just the 64MB and I can then access the BIOS so I'll see if I can increase the fsb in there. No manual I'm afraid - sourced from PC World and they didn't issue one aparently. I'll hunt about on the web for one. Trouble is I can't see who the manufacturer of the mobo is.
If you're limited then by the amount of RAM per slot and it's only happy with 64MB, the mobo only has two slots on it, so the max I could use is 128MB. Is this enough for XP to run on happily?

Thanks again


  [DELETED] 21:21 14 Aug 2003

Yes your reasoning is sound. With that sticker there I would of thought that 2 x 128mb of ram would be the max. It sounds as if you have got the ram from a good shop. Explain what has happened. They may say try two 128mb sticks and if no go, bring them back. Some small pc shops are like that, very good.

Some shops will say bring the unit in and we will try it for you, just to get the sale.

In my opinion windows X\P runs fine with 256mb of sd ram. My own machine that is networking others copes very well with it.

  [DELETED] 22:17 14 Aug 2003

Dumfy - Download a copy of AIDA32 from here click here
It's a free systen analyser tool and may identify your mobo for you.

  Dumfy 11:13 15 Aug 2003

Thanks once again to one and all.

This forum's great. Everybody is always helpful and gives useful info and advice.

I'll tick it for now.



  Dumfy 10:11 19 Aug 2003

In case this may be useful to others at a later date, I installed two sticks of PC100 SDRAM into the motherboard and it worked a treat.

System now loaded up and running XP.

Thanks for all the help


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