Cache Memory; Main Memory - HP Vectra VL5 5 Technical Reference Manual

2 System Board
Devices on the Processor-Local Bus
Setting the switches to operate at a slower speed, than the processor is
capable of supporting, can still cause erratic behavior in some case, and
would reduce the instruction throughput in others.

Cache Memory

The computer supports two levels of cache memory, each with a 32-byte line
width. The Level-1 (L1) cache memory is fabricated on the processor chip.
The Level-2 (L2) cache memory is a slower module on the system board.
Each acts as temporary storage for data and instructions from the main
memory. Since the system is likely to use the same, or adjacent, data several
times, it is faster to get it from the on-chip or on-board cache memory than
from the main memory.
The L1 cache memory is divided into two separate banks: an L1 I-cache for
instruction words, and an L1 D-cache for data words. On a P54 processor,
each has a capacity of 8 KB; on an MMX (P55) processor, each has a
capacity of 16 KB.
The L2 cache memory is controlled by the PL/PCI bridge chip in the system
board chip-set (see page 23 for a description, and details of timing patterns
and tag size). A single HP cache memory module consists of 256 KB or
512 KB of direct mapped, write-back, synchronous pipelined burst, 8.5 ns
static random access memory (SRAM). The chip-set does not support
asynchronous or burst SRAM modules.

Main Memory

There are six main memory module sockets, arranged in three banks
(A to C). One bank is already occupied by the pair of single interline
memory modules (SIMMs) that contain the 16 MB or 32 MB of memory
that is supplied with the computer.
Different banks can have different capacities (8, 16, 32 or 64 MB), but must
be composed of identical pairs of modules (2 4, 2 8, 2 16 or 2 32 MB).
By installing a pair of 32 MB SIMMs in every bank, first removing the
memory modules that were supplied with the computer, the maximum
capacity of 192 MB of main memory can be attained.
The banks can be filled, or left empty, in any order. However, there is a
performance advantage to filling the banks in the order A, B, C. The
explanation for this is outlined in the description of the cache memory
controller on page 23.
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