2--x86 Processor

The rst time a program reads a block of data it

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Unformatted text preview: emory to hold the most recently used instructions and data. The first time a program reads a block of data, it leaves a copy in the cache. If the program needs to read the same data a second time, it looks for the data in cache. A cache hit indicates the data is in cache; a cache miss indicates the data is not in cache and must be read from conventional memory. In general, cache memory has a noticeable effect on improving access to data, particularly when the cache is large. 2.1.4 How Programs Run Load and Execute Process The following steps describe, in sequence, what happens when a computer user runs a program at a command prompt: • The operating system (OS) searches for the program’s filename in the current disk directory. If it cannot find the name there, it searches a predetermined list of directories (called paths) for the filename. If the OS fails to find the program filename, it issues an error message. • If the program file is found, the OS retrieves basic information about the program’s file from the disk directory, including the file size and its physical location on the disk drive. • The OS determines the next available location in memory and loads the program file into memory. It allocates a block of memory to the program and enters information about the program’s size and location into a table (sometimes called a descriptor table). Additionally, the OS may adjust the values of pointers within the program so they contain addresses of program data. • The OS begins execution of the program’s first machine instruction. As soon as the program begins running, it is called a process. The OS assigns the process an identification number (process ID), which is used to keep track of it while running. • The process runs by itself. It is the OS’s job to track the execution of the process and to respond to requests for system resources. Examples of resources are memory, disk files, and input-output devices. • When the process ends, it is...
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This note was uploaded on 11/29/2013 for the course CSE 451 taught by Professor Hussein during the Winter '13 term at Fatih Üniversitesi.

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