Compaq AlphaServer DS20E Reference Manual page 27

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All memory and I/O components are located on a single system board that
contains a memory subsystem, PCI bus, ISA bus, integrated SCSI
fast/wide/Ultra I/O controllers, and option slots for PCI-based and ISA-based
option modules.
Processor Module
The system supports up to two processor modules that can be installed on the
system board. Each processor module contains a 21264 microprocessor. The
21264 microprocessor is a superscalar chip with out-of-order execution and
speculative execution to maximize speed and performance. It contains four
integer execution units and dedicated execution units for floating-point add,
multiply, and divide. The chip also has an integrated instruction cache and a
data cache. Each cache consists of a 64 KB two-way set associative, virtually
addressed cache divided into 64-byte blocks. The data cache is a physically
tagged, write-back cache.
The EV6 (500 MHz) processor module contains 4 MB secondary
B-cache (backup cache) consisting of late-write synchronous DRAMs (dynamic
random access memory) that provide low latency and high bandwidth. The
EV67 (667 MHz) processor module has an 8 MB DDR (dual data rate). See the
documentation that accompanies a processor upgrade for instructions on
installing additional processors.
Memory
The system supports up to four banks of memory on the system board. Each
bank contains four slots for a total of 16 slots. The system uses 200-pin buffered
synchronous dual in-line memory module (DIMMs). See Chapter 5 for
instructions on installing DIMMs.
System Overview 1-11