My RAM doesn't add up!

[Pneumatic]

When I initially built my system I put in two sticks of DDR 256MB PC2100 266MHZ RAM.

My system started getting flaky and after a long (and I mean long) process of trial and error (and with help from a few friends ) I figured out that one of the sticks of RAM had gone bad. It happened quite slowly causing random crashes and strange lockups that were becoming more and more frequent. When I ran it with only the good stick for a few days it was rock solid again.

I went out today and bought a stick of DDR 512MB PC2100 266MHZ RAM. I wanted to replace the bad 256 with a 512 to give me a total of 768 MB.

When I popped the 512 along with the good 256 stick it booted up fine and runs like a champ, but it only sees 512 MB of RAM. I have 3 slots for RAM so I changed their position and changed their order to no avail. The system will see them independently of each other, but when I put them in together 512 + 256 = 512. I cleared my CMOS and checked all of my BIOS settings and everything appears to be pretty standard.

Here are the relevant specs:
Gigabyte GA-7VTXH+ (VIA KT266A AGPset)
Athlon XP1800+
Windows XP Pro

Has anyone out there ever come across this before? If so what can I do to get it to see all of the RAM?

[LvR]

Kindness

You seem to have run into the same sort of situation I recently had with a Gigabyte GA-81RX mobo.

From the mobo manual "The mobo has 3 dimm sockets, but it can only support a maximum of 4 banks of DDR memory. DDR slot 1 uses 2 banks, DDR slot 2 and 3 share the remaining 2 banks"

Being a pesimist, I bought 3 sticks of 256M double density DDR (the biggest at the time) in anticipation of the price increases at 40% less than at the time the mobo actually arrived.

Comes the time the mobo eventually arrived my 3 sticks of 256M (768M) ram is now seen as only 512M (256+128+128).!

Guess who is in the market for a stick of 512M double density DDR at a much higher price?

[GT98]

I know with my KG-7 RAID with the AMD 760 North Bridge I'm stuck using Registered DDR RAM in pairs when I popluate my RAM slots. I think the same applies to the VIA266A aso.

Scott