TYAN THUNDER I7501 XTREME Manual page 16

Memory Pair Installation
You must install the first two memory modules in DIMM A1 and DIMM B1. Both modules
must be the same in both size and density. Modules must also use the same chip configuration.
Each module that is installed must physically have the same number of memory chips on them.
All memory sockets must be populated by the same memory type, either x4 modules or x8 You
cannot mix and match x4 and x8 modules together.
A few things to remember:
At least TWO Registered ECC DDR SDRAM modules must be installed for the system
to turn on and POST (Power On Self Test) and DIMM modules must be installed in
pairs.
When installing modules, install them in this order: A1, B1, A2, B2, etc.
The Thunder i7501 Xtreme supports up to 12GB of memory with 2GB registered DDR
128MB, 256MB, 512MB, 1GB, and 2GB Registered PC2100/PC1600 DDR SDRAM
memory modules are supported in x4 or x8 configuration
Use ONLY x8 OR x4 type memory modules. Mixing memory types may affect stability.
RAM chips are organized as x4 bits or x8 bits. On a memory module you're just lining all
these chips up in parallel so you have a 64-bit wide data bus. All 512MB modules are
made using 16 piecesc of either 64Mbit x4, or 32Mbit x8. If you use sixteen x8 chips you
would get a 128-bit data bus, so it has to be split into two separate banks. Each with 64-
bit bus. That's why 512MB modules based on x8 chips are dual bank. To build 256MB
modules you can either use sixteen 32Mx4 chips, or eight 32Mx8 chips. But you can't
build a 256MB module using 64Mx4 chips. To build 1GB modules you have to use
thirty-two 64Mx4 chips. Two 64Mx4 chips are stacked on top of each other with a lead
frame in between. Stacking basically converts two 64Mx4 chips into one 128Mx4 chip or
one 64Mx8 chip. Then you stick 16 stacks onto a PCB. Stacking also saves real estate,
so you can fit more chips onto a shorter PCB and keep trace lengths in spec.
If you are still unsure whether you are using x4 or x8 memory you can research the memory chip
by the SDRAM part numbers, or go to http://www.google.com
16
http://www.TYAN.com
and search for jedec 21-c 4.20.4.