Secondary-Storage Management

I/O System Management

File Management

Main-Memory Management

Primary-Memory or Main-Memory is a large array of words or bytes. Each word or byte has its own address. Main-memory provides storage that can be access directly by the CPU. That is to say for a program to be executed, it must in the main memory.

The major activities of an operating in regard to memory-management are:

Keep track of which part of memory are currently being used and by whom.

Decide which process is load ed into memory when memory space becomes available.

Allocate and deallocate memory space as needed.

A file is a collected of related information defined by its creator. Computer can store files on the disk (secondary storage), which provide long term storage. Some examples of storage media are magnetic tape, magnetic disk and optical disk. Each of these media has its own properties like speed, capacity, and data transfer rate and access methods.

A file system is normally organized into directories to ease their use. These directories may contain files and other directions.

The five main major activities of an operating system in regard to file management are

The creation and deletion of files.

The creation and deletion of directions.

The support of primitives for manipulating files and directions.

The mapping of files onto secondary storage.

The back up of files on stable storage media.

I/O subsystem hides the peculiarities of specific hardware devices from the user. Only the device driver knows the peculiarities of the specific device to which it is assigned.

Generally speaking, systems have several level s of storage, including primary storage, secondary storage and cache storage. Instructions and data must be placed in primary storage or cache to be reference d by a running program. Because main memory is too small to accommodate all data and programs, and its data are lost when power is lost, the computer system must provide secondary storage to back up main memory. Secondary storage consists of tapes, disks, and other media designed to hold information that will eventually be accessed in primary storage (primary, secondary, cache) is ordinarily divided into bytes or words consisting of a fixed number of bytes. Each location in storage has an address; the set of all addresses available to a program is called an address space.

The three major activities of an operating system in regard to secondary storage management are:

Managing the free space available on the secondary-storage device.

Allocation of storage space when new files have to be written.

Scheduling the requests for memory access.

Дата добавления: 2015-03-31