Main Memory

The Operating System as a Resource Manager
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The Operating System as a Resource Manager

The idea of an operating system as primarily providing abstractions to application programs is a top-down view. An alternative, bottom-up, view holds that the operating system is there to manage all the pieces of a complicated system. Present computers contain processors,

Memory
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Memory

The second major element in any computer is the memory. Preferably, a memory should be very fast (faster than executing an instruction so the CPU is not held up by the memory), abundantly large, and dirt cheap. No current technology satisfies all of these goals

Disks
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Disks

Next in the hierarchy is magnetic disk (hard disk). Disk storage is two orders of magnitude cheaper than RAM per bit and often two orders of magnitude larger as well. The only problem is that the time to randomly

Address Spaces
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Address Spaces

Every computer has some main memory that it uses to hold executing programs. In a very simple operating system, only one program at a time is in memory. To run a second program, the first o

Layered Systems
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Layered Systems

A generalization of the approach of figure in previous article i.e. "OPERATING SYSTEM STRUCTURE" is to organize the operating system as a hierarchy of layers, each one constructed upon the one below it. The first system constructed in this way was the THE

SCHEDULING
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SCHEDULING

When a computer is multiprogrammed, it often has multiple processes or threads competing for the CPU simultaneously. This situation happens whenever two or more of them are in the ready state at the same time. If only one CPU is available, a choice has to be made which

FILE SYSTEM MANAGEMENT AND OPTIMIZATION
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FILE SYSTEM MANAGEMENT AND OPTIMIZATION

Making the file system work is one thing; making it work efficiently and robustly in real life is another thing. In the following sections we will examine some of the issues involved in managing disks.

The MS-DOS File System
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The MS-DOS File System

The MS-DOS file system is the one the first IBM PCs came with. It was the main file system up through Windows 98 and Windows ME. It is still supported on Windows 2000, Windows XP, and Windows Vista, although it is no longer standard on new PCs now except for floppy disks.

Direct Memory Access (DMA)
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Direct Memory Access (DMA)

Regardless of whether a CPU does or does not have memory-mapped I/O, it needs to address the device controllers to exchange data with them. The CPU can request data from an I/O controller one byte at a time but doing so wastes the CPU's time, so a different scheme, called

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