Exam 17: Looking Under the Hood

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Instructions per clock cycle. Suppose that during each clock cycle, a processor could perform three instructions instead of one. It would perform three times as much work in the same amount of time. Processors that execute multiple instructions per clock cycle are referred to as superscalar . CPU cache. Before processing can take place, data and instructions exist in RAM chips located several inches away from the processor on the system board of your PC. Even traveling at the speed of light, data can require several clock cycles to move from RAM to the processor. A CPU cache (pronounced "cash") is data-holding circuitry from which instructions and data can be accessed faster than from RAM. Typically, cache is measured by its storage capacity in kilobytes (KB) and by the number of cache areas or levels. Most of today's microprocessors have multi-level caches, so you might see references to L1 (Level 1), L2, or L3 caches in advertising materials. Accelerated front side bus. The circuitry that transports data to the microprocessor is called the front side bus (FSB). A fast front side bus moves data quickly and allows the processor to work at full capacity. Processor manufacturers use a variety of techniques, such as HyperTransport and QuickPath, to accelerate the rate at which data travels to the processor. Extended instruction sets. All x86 processors have a core set of instructions. However, some processors have extended instruction sets that speed up certain types of processing, such as video or photo processing. Multi-core architecture. A multi-core processor is a single microprocessor chip with circuitry that allows it to process more than one instruction at a time. For example, the Intel Core i7 chip contains four processing cores, which theoretically allow the i7 to process instructions four times as fast as a single core processor. In practice, however, a multi-core processor offers maximum performance only when your computer's operating system and application software are optimized for multi-core processing. Windows supports multi-core processing, as do some games and graphics software. W ord size. Microprocessors work with instructions and data composed of bits. Word size refers to the number of bits that a microprocessor can manipulate at one time. Word size is based on the size of registers in the processor and the capacity of circuits that lead to those registers. Today's personal computers typically contain 64-bit processors that have 64-bit registers and process 64 bits at a time. A few 32-bit processors are still in use, primarily for netbook computers. Processors with a larger word size can process more data during each processor cycle-a factor that leads to increased performance.