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Dale - Computer Science Illuminated 242

Dale - Computer Science Illuminated 242 - using the...

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7.6 Other Important Threads 215 7.6 Other Important Threads In the last chapter, we talked about threads that are important in computing: information hiding, abstraction, naming things, programming languages, and testing. All of these threads have appeared in this chapter, emphasizing how intertwined they all are. At the machine-language level, there is very little information hiding going on. Every little detail must be explicitly taken care of. One bit of information was hidden: Pep/7 uses 2’s complement to represent negative numbers, but we did not need to know this to use the machine language. (See Chapter 2 to refresh your memory about 2’s complement.) When we move up to the assembly-language level, we can hide some of the details
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Unformatted text preview: using the abstractions that the language provides. For example, we are able to set up a block of storage and give the first byte in the block a name by which we can refer to the block. We can associate a word of storage with a name and store a value into the word. We can give an instruction a name and branch to the instruction. These examples of abstraction involve giving names to data or actions. The idea that we can give a name to an action as we did with the instruction we called Main that loads the sum into the accumulator is an extremely important concept, upon which we dwell at some length in later chapters....
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