Computer Architecture
The Anatomy of Modern Processors
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Superpipelined Processors
In contrast to a superscalar processor, a
superpipelined one has split the main computational pipeline into more stages.
Each stage is simpler (does less work) and thus the clock speed can be
increased. However the latency, measured in clock cycles, for any
instruction to complete has increased from 4 cycles in early RISC processors to
8 or more.
Benefit
The major benefit of superpipelining is the increase in the
number of instructions which can be in the pipeline at one time and hence the
level of parallelism.
Drawbacks
The larger number of instructions "in flight" (ie in
some part of the pipeline) at any time, increases the potential for data
dependencies to introduce stalls. Simulation studies have suggested that a
pipeline depth of more than 8 stages tends to be counter-productive.
Note that some recent processors, eg the MIPS R10000, can be described
as both superscalar - they have multiple processing units - and
superpipelined - there are more than 5 stages in the pipeline.
© John Morris, 1998