What Is The Computer System Concept

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The primary storage unit (also called main memory) holds data and instructions between processing steps and supplies them to the control unit and arithmetic-logic unit during processing.All data and programs must be placed in memory before they can be used in processing.

The primary storage unit is also used to hold data and program instructions between processing steps and after processing is completed but before output. In modern computers, the primary storage unit consists of microelectronic semiconductor memory chips. Most of memory is known as RAM (random access memory). The contents of these memory chips can be tnstattfty dmugfid to store view data.. Other, more permanent, memory are card ROM (read only memory).Thomas Sabo

Data and programs are also stored in secondary storage devices, such as magnetic disk and tape units, which greatly enlarge the storage capacities of computer systems. Also, since memory circuits typically lose their contents when electric power is turned off, most secondary storage media provide a more permanent type of storage. However, ...
... the contents of secondary storage devices cannot be processed without first being brought into the primary storage unit. Thus, external secondary storage devices play a supporting role to the primary storage unit of a computer system. For example, programs and files are typically stored until needed on magnetic floppy disks and hard disks on microcomputer systems, and on large magnetic tape disk and tape units on larger computer systems.

Computer Storage Capacities. Data is processed and stored in a computer system through the presence or absence of electronic or magnetic signals in the computer's circuitry or in the media it uses. This is called a two-state or binary representation of data, since the computer and the media can exhibit only two possible states or conditions. For example, transistors and other semiconductor circuits are either in a conducting or no conducting state. Thus, for electronic circuits, the conducting (ON) state could represent the number one, while the no conducting (OFF) state could represent the number zero.
The smallest element of data is called a bit, or binary digit, which can have a value of either zero or one. The capacity of memory chips is usually expressed in terms of bits. A byte is a basic grouping of bits that the computer operates as a single unit. It typically consists of eight bits and is used to represent one character of data in most computer coding schemes.Thomas Sabo Jewelry Thus, the capacity of a computer's memory and secondary storage devices is usually expressed in terms of bytes.

Storage capacities are frequently measured in kilobytes (abbreviated as KB or K) or megabytes (abbreviated as MB or M). Although kilo means "one thousand" in the metric system, the computer industry uses K to represent 1, 024 (or 210) storage positions. Therefore, a memory size of 640K, for example, is really 655, 360 storage positions, rather than 640, 000 positions. However, such differences are frequently disregarded in order to simplify descriptions of storage capacity. Thus, a megabyte is roughly 1 million bytes of storage, while a gigabyte is roughly 1 billion bytes and a terabyte represents about 1 trillion bytes. Typically, computer primary storage capacities range from 640 kilobytes to 128 megabytes for microcomputer systems. Magnetic disk capacities generally range from 360K bytes to several megabytes for floppy disks, over tens of gigabytes for hard disk drives, and over 500 megabytes for an optical disk. Mainframe magnetic disk units supply many gigabytes of online storage.