I have a HP Brio600 and have installed 512mb ram but it only sees 256 even though HP say it will see 512. Im told that the PC needs to be 128bit not 64bit to see the extra ram. Can I change to 128 on my pc?

Don't confuse "bits" with "Mbits"...RAM density is expressed in Mbits.

To determine the density of your RAM, take the total capacity of the module, divide by the number of chips on the module, then multiply by 8. If the number is 256 or higher, you have high density RAM. Just to explain...if you have a double sided (16 chips) stick of 512MB, 512/16 x 8 = 256Mbit techology. If it only has 8 chips, 512/8 x 8 = 512Mbit technology. Therefore, 512MB RAM can ONLY be either 256Mbit or 512Mbit density, which means ALL 512MB modules are high density.

Another thing to look at is your board's "per slot" capacity. If your board's total RAM capacity is 768MB & you have 3 slots, the max module size per slot would be 256MB (768/3). Obviously if this is what you have, a 512MB stick can only be recognized as 256MB, if at all.

I just visited the PNY memory website to inquire about a unrelated memory issue, but I saw the following & thought I'd pass it along:

"Important Announcement
PC133 Modules are NO LONGER backward compatible with PC100 Machines. To determine the correct memory upgrade for your machine, use the PNY memory configurator."

Here's another site:

http://www.kingston.com/support/faqs/memory/general_14.asp

Asus A7N8X-X
1800+ @ 8 x 210MHz
512MB PC3200
Asus Ti4200 128MB
WinME/WinXP Pro

Help!!!! Basically I have 2 slots on the motherboard. The PC is supposed to be PC133 compatable up to a total of 512mb. So I have 2 x 256mb sticks of PC133. It sees one but not 2nd.