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3 System Board (P/Ns D3657-63001 and D3661-63001)
Devices on the Processor Local Bus
Using the pipelines halves the instruction execution time and almost
doubles the performance of the processor, compared with an Intel486
microprocessor of the same frequency.
Floating Point Unit (FPU)
The Floating Point Unit incorporates optimized algorithms and dedicated
hardware for multiply, divide, and add functions. This increases the
processing speed of common operations by a factor of three.
Dynamic Branch Prediction
The Pentium processor uses dynamic branch prediction. To dynamically
predict instruction branches, the processor uses two prefetch buffers. One
buffer is used to prefetch instruction code in a linear way, and the other to
prefetch instruction code depending on the contents of the Branch Target
Buffer (BTB). The BTB is a small cache which keeps a record of the last
instruction and address used. It uses this information to predict the way that
the instruction will branch the next time it is used. When it has made a
correct prediction, the branch is executed without delay, thereby enhancing
performance.
Instruction and Data Cache
The Pentium processor has separate on-chip code and data caches. Each
cache is 8 KB in size with a 32-bit line. The cache acts as temporary storage
for data and instructions from the main memory. As the system is likely to
use the same data several times, it is faster to get it from the on-chip cache
than from the main memory.
Each cache has a dedicated Translation Lookaside Buffer (TLB). The TLB is
a cache of the most recently accessed memory pages. The data cache is
configured to be Write-Back on a line-by-line basis (a line is an area of
memory of a fixed size).
The data cache tags (directory entries used to reference cached memory
pages) are triple-ported to support two data transfers and an inquire cycle
in the same clock cycle. The code cache tags are also triple-ported to
support snooping (a way of tracking accesses to main memory by other
devices) and split line accesses.