Hi folks, My first post here, so I'm hoping somebody can help! I have a Compaq Presario 2500, model 2548AI, made 2002. This laptop was supplied with a Hynix 256MB PC2700 DDR333 SODIMM, Compaq part, which goes OK though the manual (and the HP site) says it takes a 266MHz PC2100.

I have tried to upgrade with 2 x Legend 512MB PC2700 DDR333 SODIMMs, but the computer will not boot. The manual says that it should take up to 1GB of RAM in two 512MB modules.

Both the original 256 card and the new 512 cards use the same brand of chips, and seem to have the same specs: DDR333, unbuffered, 2.5v, CAS latency 2/2.5, and have eight Hynix chips per card.

I have tried the 512 cards in both slots - no boot! But the laptop does boot with the 256 card in slot one and a 512 in slot 2. However BIOS only reports the 256 RAM, and there is no option for selecting more.

It has been suggested to me that HP somehow fix their their laptops so they only take HP supplied parts, which of course cost up to three times more than similar third party parts. Is this correct? My thoughts are that any comapatible RAM cards should work?

Legend memory is trouble.
You can use PC2700 PC3200 memory if it is all identical.. but I would use Crucial, Corsair, Kingston, Infineon, or Hypnix.
Maximum of 512 MB per slot...
But mixing memory brands and module sizes will get your right where you don't want to be.
To be safe: Two 512 MB modules of PC2700 will work in that model.
What you heard about HP is simply bull only
Go to www.zipzoomfly.com for identical modules at $35.90 to 45.60 per module... avoid value ram or value select sodimms.

Thank you for your reply raybay! What is wrong with Legend memory? I have used it before in my desktops, without any problems. I would have thought that replacing a PC2700 256MB RAM with a PC2700 512MB RAM should be OK, particularly when both have chips of the same brand? I actually previously tried a pair of 512MB PC3200 RAM cards, but they did not work either.

http://www.techspot.com/vb/topic65114.html

just about every laptop i've bought for work (over 20, varying in make) are fussy with ram.
You can't just go for quality and think it will be alright, you tend to have to look for manufacturer certified ram. Some 240 pin sticks are actually about .5mm longer than others and simply won't fit in certain laptops.
Its a ball ache, but you 'may' have to pay over the odds for the right ram.