Operating_systems-page23

Operating_systems-page23 - Jelena Mamenko Operating Systems...

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Jelena Mamčenko Operating Systems Lecture Notes on Operating Systems 23 are included as part of the file COMMAND.COM and remain resident in memory at all times; e.g., DIR and COPY). The command processor is also a file you see on the disk, but once read into the computer's memory, it usually resides there. Some programs provide their own command processor, and there are times when the command processor will be overwritten in memory by a program and have to be reloaded when the program stops executing. The input/output system consists of two files and a ROM (Read Only Memory) chip. While the two files are on your disks and are loaded into memory when the computer starts, they are normally hidden from your view and not available to you for changing. 22 Input/Output System This most primitive of the DOS systems has two parts: BIOS (Basic Input/Output System). These are the fundamental routines that control the keyboard, video display and other peripherals. The BIOS is comprised of a ROM on the computer's main circuit board and the file IBMBIO.COM (or IO.SYS), one of the two
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