Dale - Computer Science Illuminated 147

Dale - Computer Science Illuminated 147 - use the generic...

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Addressability The number of bits stored in each addressable loca- tion in memory Figure 5.1 The von Neumann architecture Input device Output device Auxiliary storage device Memory unit Arithmetic/logic unit Control unit Central Processing Unit ± The arithmetic/logic unit that is capable of performing arithmetic and logic operations on data ± The input unit that moves data from the outside world into the computer ± The output unit that moves results from inside the computer to the outside world ± The control unit that acts as the stage manager to ensure that all the other components act in concert Memory Recall from the discussion of number systems that each storage unit, called a bit, is capable of holding a one or a zero and that these bits are grouped together into bytes (8 bits) and that bytes are grouped together into words. Memory is a collection of cells, each with a unique physical address. We
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Unformatted text preview: use the generic word cell here rather than byte or word, because the number of bits in each addressable location, called the memorys address-ability , varies from one machine to another. However, most computers are byte-addressable today. The ad in the previous section describes a memory of 128,000,000 bytes. This means that each of the 128M bytes is uniquely addressable. Therefore, the addressability of the machine is 8 bits. The machine being described could have as many as 4,294,967,296 bytes of memory, but only 128MB are being provided. Where did that figure of possible number of bytes come from? It is 2 32 . The Pentium IV processor mentioned in the ad is a 32-bit machine. This means that the processor can distinguish 2 32 120 Chapter 5 Computing Components...
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