We recommend viewing “PC Basic Components" (PH_07_04.swf) here. You can find this media asset on the Instructor Resource Center CD-ROM or online at www.computerconfluence.com.
In most cases the actual execution of an instruction is performed by the CPU’s arithmetic logic unit (ALU) . The ALU includes registers , each usually 32 or 64 bits in size. Program instructions are stored in primary storage (memory), which is usually on chips outside the CPU. The CPU’s first task is to read an instruction from memory. The bus unit handles all communication between the CPU and primary storage. The prefetch unit , or prefetcher, instructs the bus unit to read the instruction stored at a particular memory address. This unit not only fetches the next instruction to execute, but it also fetches several subsequent instructions to ensure that an instruction is always ready to be executed. The decode unit takes the instruction read by the prefetcher and translates it into a form suitable for the CPU’s internal processing. It does this by looking up the steps required to complete an instruction in the control unit. If an instruction requires that information be sent out from the CPU—for example, written into memory—then the final phase of execution is writeback , in which the bus unit writes the results of the instruction back into memory or some other device. Microprocessor manufacturers use many techniques to eliminate bottlenecks and speed up processing. For example, in the same way it prefetches the next likely instructions to be read, the CPU prereads the next likely data to be used into a cache in memory (called a Level 2 cache (L2 cache) or, for faster access, in the CPU itself (a Level 1 cache ).
http://www.intel.com/: The INTEL Web site; it’s a great source of extra information on this subject. http://www.apple.com/: The Apple Web site; it’s also a great source of information on this subject.
http://www.intel.com/: The INTEL Web site; it’s a great source of extra information on this subject. http://www.apple.com/: The Apple Web site; it’s also a great source of information on this subject.
When you turn on the computer, the CPU automatically begins executing instructions stored in read-only memory (ROM). On most computer systems, ROM also contains parts of the operating system. The firmware programs in ROM are sometimes called the BIOS (basic input/output system) . The executing instructions help the system start up and tell it how to load the operating system—copy it from disk into memory. Once executing instructions are loaded into memory, the CPU is able to execute them.
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