why does my pc not recognise all my memory?

  JEFoord 20:58 05 Nov 03


I have just installed some extra ram into my pc but it wont recognise all of it.
I bought the pc with 64mb installed. Decided I needed some more and so bought 128mb stick.
in the spare slot i have inserted this 128mb stick, but my pc tells me i only have 128mb total. but surely i have 192mb total?
i have tried swapping the slots i use for the 64 and 128mb but still only 128 total.
it doesnt matter which slot i put the 128mb in, the pc recognises it, but weather i have the 64mb in the other slot or not, it makes no difference.
is there anything i can do to make my pc recognise the extra ram?
i am running windows 98 2nd edition and have definately got the right type of memory. could it be my motherboard?
any suggestions would be very welcome.

  john-232317 21:16 05 Nov 03

I think they have to be equal pairs, ie two 64 or two 128

  Jezzer1 22:01 05 Nov 03

dadyassa is right. You can only add RAM in multiples of the same amount. But what I would like to know is WHY ??

  ? ???K??M? 22:04 05 Nov 03

You can add any amount on an AMD pc think it only pentium based pcs where you need to add them in pairs, could be wrong tho.


  JEFoord 22:05 05 Nov 03

that would explain things i suppose, thanks guys.
my pc is about 4 years old, do you think it would be able to accept 2 x 128mb cards or would the motherboard object?

  no.good.at.all 22:37 05 Nov 03

my old celeron unit used to ru anything of any multiple i used to run 192 mb it showed up as 196 with on board

  DieSse 22:47 05 Nov 03

The problem you have is not about units of the same capacity, but a limitation in motherboard design.

Older motherboards (from 3-4 years age) have a constraint on the way they address RAM modules - it's all to do with the organisation on the RAM module, and the type of chips used. Modern modules require extra addressing lines which older motherboards don't have.

The upshot is that you only see half the amount of RAM on the new board. You need a specific RAM module type, sometimes called "double - sided".

See here for a reference click here

Whilst the term "double-sided" is often used in relation to modules with the lower address line requirement, it's not strictly accurate - as even the newer modules can still have chips on both sides of the module.

  woodchip 22:47 05 Nov 03

Not correct, sorry but you can add memory of different sizes, As that's what I have in an old AT AMD K6 500 system three different sizes of SDRAM starting with the big one in number 0 slot down to the small one in number two slot and it is all recognized. There are various reasons why it cannot be recognized you have said that it is the correct memory but is it compatible with the memory that you have already got in that's just as important

  roy 22:52 05 Nov 03

I agree with no.good.at.all.

My old pc is a Pentium lll 500 with 192 Mb of sdram. One stick is 64 the other 128. I can't remember which was fitted when I bought the pc but had no trouble upgrading it. On the other hand an earlier pc with a Pentium 100 needed its ram to be in matching pairs. I can't remember the type of ram used though.

  DieSse 22:54 05 Nov 03

Woodchip is correct - you can mix RAM of different sizes. But it's not (in this case)about compatability between the modules - but compatability with the motherboard.

I come across this frequently when upgrading older systems.

You can still buy both types of 128Mb modules - the older style are usually more expensive though.

The Crucial web site claims to take this into account if you use their module selector, and to only supply the correct type.

  JEFoord 22:56 05 Nov 03

i have a pentium 3 450. so i wouldn't think it was that much older than yours.

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