Lenovo ThinkPad 770 Technical Reference Manual for the ThinkPad 770 - Page 24

Description This section describes the microprocessor, connectors, memory subsystems, and miscellaneous system functions and ports for the ThinkPad computers. Microprocessor The ThinkPad 770 uses the Intel Pentium® 200 or 233 MHz processor with the MMX™ technology. The Processor has a 32-bit address bus and a 64-bit data bus. It is software-compatible with all previous microprocessors. The Processor has an internal, split data and instruction, 32KB write-back cache. It includes pipelined math coprocessor functions and superscalar architecture (two execution units). Cache Memory Operation In addition to the 32 KB of internal Level 1 (L1) cache memory in the microprocessor, the system board of the ThinkPad 770 computer contains an additional 256 KB of external Level 2 (L2) cache memory. The cache memory in the Intel Pentium microprocessor and the L2 external cache memory enable the microprocessor to read instructions and data much faster than if the microprocessor had to access system memory. When an instruction is first used or data is first read or written, it is transferred to the cache memory from main memory. This enables future accesses to the instructions or data to occur much faster. The cache is disabled and empty when the microprocessor comes out of the reset state. The cache is tested and enabled during the power-on self-test (POST). The cache memory in the Intel Pentium microprocessor is loaded from system memory in 32-byte increments, each referred to as a cache line. A cache line is aligned on a paragraph boundary. A reference to any byte contained in a cache line results in the entire line being read into the cache memory (if the data was not already in the cache). When the microprocessor gives up control of the system bus, the cache memory enters "snoop" mode and monitors all write 2-2 System Board