Compaq AlphaServer DS20 Service Manual page 23

Memory Variants
Memory is organized on two 256 plus ECC bit buses. Each bus can hold up to two
memory banks (a memory option) made up of four DIMM modules. Memory can be
configured from a minimum of 128 Mbytes (1 MS340-BA) to 4 Gbytes (4 MS340-
EA). All memory is synchronous.
Option Size
MS340-BA 128 MB
MS340-CA 256 MB
MS340-DA 512 MB
MS340-EA 1 GB
Memory Operation
Two 256-bit memory buses transfer data between the cross-bar chipset switch and
main memory. Each DIMM bank, made up of four DIMM modules, provides the data,
or 256 bits plus 32 ECC bits, of the 32 bytes transferred. Two modules in the bank
provide the odd bytes of data, and the other two modules provide the even bytes of
data.
Memory Configuration Rules
In a system, memories of different sizes are permitted, but:
•
A memory option consists of four DIMMs all of which must be the same size.
•
Convention places the largest memory option in slots marked 0 on the system
board. See Figure 1-6.
•
Memory options must be installed in slots designated for each bank. The first
bank goes into slots marked 0, the second bank into slots marked 1, and so on.
Module Type
54-25066-BA Synch.
54-25053-BA Synch.
54-25941-KA Synch.
54-25941-BA Synch.
DRAM
Number/
option Size
36 4 x 32MB
36 4 x 64MB
36 4 x 128MB
36 4 x 256MB
System Overview 1-13