One can find all information about computer fundmentals and C programming.
Wednesday, December 8, 2010
CPU Primary and Secondary Storage
The CPU contains circuits that control and executeinstructions by using some type of MEMORY. Memoryis referred to by size, such as 16K, 32K, 64K, and so on.The "K" represents the value of 1,000. Therefore16,000 is 16K.Semiconductor memory consists of hundreds ofthousands of tiny electronic circuits etched on a siliconchip. Each of these electronic circuits is called a BITCELL and can be in either an OFF or ON state torepresent a 0 or 1 bit. This state depends on whether ornot current is flowing in that cell. Another name usedfor semiconductor memory chips is integrated circuits(ICs). Developments in technology have led tolarge-scale integration (LSI) that allows more and morecircuits to be squeezed onto the same silicon chip.Some of the advantages of semiconductor storageare fast internal processing speeds, high reliability, lowpower consumption, high density (many circuits), andlow cost. However, there is a drawback to this type ofstorage. It may be VOLATILE, which means it requiresa constant power source. When the power for yoursystem fails and you have no backup power supply, allof the stored data is lost.Primary StorageTwo classifications of primary storage with whichyou should become familiar are read-only memory(ROM) and random-access memory (RAM).READ-ONLY MEMORY (ROM).—In computers,it is useful to have instructions that are used often,permanently stored inside the computer. ROM enablesus to do this without loosing the programs and datawhen the computer is powered down. Only thecomputer manufacturer can provide these programs inROM; once done, you cannot change it. Consequently,you cannot put any of your own data or programs inROM. Many complex functions, such as translators forhigh-level languages, and operating systems are placedin ROM memory.Since these instructions are hardwired, they can beperformed quickly and accurately. Another advantageof ROM is that your imaging facility can orderprograms tailored for its specific needs and have theminstalled permanently in ROM. Such programs arecalled microprograms or firmware.RANDOM-ACCESS MEMORY (RAM).—RAMis another type of memory found inside computers. It may be compared to a chalkboard on which you canscribble down notes, read them, and erase them whenfinished. In the computer, RAM is the workingmemory. Data can be read (retrieved) or written(stored) in RAM by providing the computer with anaddress location where the data is stored or where youwant it to be stored. When the data is no longerrequited, you may simply write over it. Thus you canuse the storage location again for something else.Secondary StorageSecondary storage, or auxiliary storage, is memoryexternal to the main body of the computer (CPU) whereprograms and data can be stored for future use. Whenthe computer is ready to use these programs, the data isread into primary storage. Secondary storage mediaextends the storage capabilities of the computer system.Secondary storage is required for two reasons. First, theworking memory of the CPU is limited in size andcannot always hold the amount of data required.Second, data and programs in secondary programs donot disappear when the power is turned off. Secondarystorage is nonvolatile memory. This information is lostonly when you erase it. Magnetic disks are the mostcommon type of secondary storage. They may be eitherfloppy disks or hard disks (hard drives).PERIPHERAL DEVICESPeripheral devices include all the input and outputdevices used with a computer system. When thesedevices are under control of the CPU, they are said tobe on line. When they perform their functionindependently, not under direct control of the CPU, theyare said to be off line. The following peripheral devicesare used commonly for input and output. Those thatperform only input are marked (I), those that performonly output are marked (O), and those that perform bothinput and output are marked (I/O).Optical Character Reader (I)An optical character reader reads printed data(characters) and translates it to machine code.Keyboard (I)The keyboard is used by a computer operator tocommunicate with a computer system.