3System 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.

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