Main Memory - HP Vectra XU 6/XXX Optimization Manual

MAIN MEMORY

The main memory in your PC consists of two, four, six or eight Double Interline Memory
Modules (DIMMs). 16 MB of memory is fitted as standard (two 8 MB modules) and can be
upgraded to a maximum of 256 MB. Memory modules are available in three capacities: 8 MB,
16 MB and 32 MB. The maximum memory capacity (256 MB) is obtained by installing eight
32 MB DIMM modules.
NOTE
128-bit Memory
Each DIMM module stores 64 bits of data plus 8-bits of Error Correcting Code (ECC) code.
Access to the memory modules is controlled by a memory controller on the processor's local
bus. This controller manages the modules in pairs to create single, 128-bit wide logical banks.
The processor's local data bus is 64 bits wide. All data written to or read from the memory is
transferred on this bus. The memory modules are accessed by the memory controller through
two, parallel 64-bit data paths. The memory controller connects these two 64-bit data paths with
the processor's bus by interleaving the accesses. This means that consecutive 64-bit accesses
to a memory bank are made to different modules.
By using interleaving to access the memory banks, the memory controller actually increases
the speed of your PC's memory. This is because of the characteristics of the memory
components used.
Main memory uses a type of memory component called Dynamic Random Access Memory
(DRAM). DRAM stores data in a rectangular array, so that each data item corresponds to an
address (location) which is formed of two parts. These two parts must be sent to the DRAM in
separate clock cycles, which means that the data cannot be read from or written to the DRAM
in the same clock cycle as the memory controller begins to access it.
The DIMM modules used by your HP Vectra XU PC
use a 5 volt power source. DIMM modules that use a
3.3 volt power source are not supported and must not
be installed.