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y o c u -tr a c k c Rereen normally required if errors are encountered Data is not current Error correction is more difficult Question Online Processing System? - Def: Inputs data enters the computer directly as soon as it is being transacted There information will be processed immediately and updated into the master file - Ads: Enter availability of information for decision making More accurate data capture Schedules suits user - Dis: CPU time is used less efficiently Random arrival of transactions, terminal operator process each transaction separately More expensive than batch processing Question Real Time Processing System? - Def: One which controls the environment by receiving data processing them and returning results sufficiently quickly to affect the functioning of the environment at that time - Ads: Response time is very critical and sufficient quick - Dis: Expensive hardware & software Very complex in terms of hardware & software Chapter 4: PRINTERS AND TERMINALS Question Classification of printers? Classifying printers according to speed a Serial printers Slow printers that print one character at a time Eg: Dot matrix printers Daisywheel printers b Line printers Medium to high speed printers that can print in excess of 2000 lines per minute Eg: Chain Printers Band Printers Drum Printers Calssifying printers according to method of printing a Impact printers Use hammers or prints to strike a print rebbon in order to form the character on the paper b Non impact printers Use more silent methods of printing Eg: Thermal printers Ink Jet printers Lazers printers Classifying printers according to print quality d o m o w w w d o C lic k to bu y bu to k lic C w w w N O W ! h a n g e Vi e N PD ! XC er O W F- w m h a n g e Vi e w PD XC er F- c u -tr a c k c y o c u -tr a c k c Kinds of quality printers Draft quality Near letter quality(NLQ) Letter quality Graphic quality Question Describe some types of printer? According to speed: a Dot matrix printer - Serial impact printers that can print draft, near letter quality and a limited amount of graphics - The print resolution is generally lower than lazer printers b Daisywheel printers - Are serial impact printers, the speed of a daisywheel printer is slow(20-55 characters per second), noisy in operation - The print head has the letters arranged at the end of spokes round a central hub c Chain printers - The chains printers has its characters set rapidly rotating on a print chain d Band printers - The band printer has rotating scalloped steel band e Drum printers - Are line printers, the print character are raised in bands around a heavy metal drum which rotates at very high speed - The print hammers strike the paper and a print ribbon against an apropriate character on the line An entire line of the same character is printed on one rotation of the drum f Thermal printers - Uses special heat sensitive paper and a matrix of print wires that become hot when exposed to an electric current The heated wires come into close contact with the paper, burning the image of the character onto it - The more advanced thermal printers are using thermal transfer printing - They have a special heat sensitive ribbon and a print head with wires that become hot when a currents is applied - The heat from the print wires causes the ink from the ribbon to fuse to a piece of regular paper g Inl Jet Printers - The ink jet prints by using a small droplet generator to break special inks into tiny drops, which are then forced towards a paper supply h Lazer printers - Using a photoconductive drum - A lazer is then used to write the image of the character onto the drum - After exposure to the lazer, the drum rotates through a developing station, picks up toner and transfers it to the paper - The character is fused onto the paper by heat i Ion deposition printers - Ions are created in a cavity, and directed electrically through an orifice onto the dielectric surface of a rotating cylinder .d o m o w w w d o C lic k to bu y bu to k lic C w w w N O W ! h a n g e Vi e N PD ! XC er O W F- w m h a n g e Vi e w PD XC er F- c u -tr a c k c y o c u -tr a c k c - The required characters are formed as an electric charge image on the cylinders surface - Toner is the applied to the charged image and transferred to the paper on which it is transfixed by pressure(cold fusion) j Electrostatic printers - Letterheads and logos are created electrostatically from a changeable metal cylinder k Magnetic printers - A drum in the printer has a surface that can be coated with sows of tiny spots of magnetion by means of thousands of minute recording heads - As the drum rotates it becomes covered with these magnetic spots so as to from a latent image of the page to be printed - Dry ink particles are brought into contact with the drum’s surface and these adthere to the magnetised spots The ink was then pressunal on to the surface and subsequently transferred onto the paper Question Characteristics of a page printers? - Speed - Characters sets - Copies - Intelligence - Output Chapter 5: DATA STORAGE MEDIA Question Data storage Requirements Characteristics? - Low access time: fast speed - Storage capacity: much enough - Interchangeability: can be change easily - Security: safe enough - Transfer rate: fast enough - Cost: economic Question Magnetic disks? - This comprises a drive unit onto which one or perhaps two magnetic disk cartridges are loaded - The drive consists of a control unit and a spindle housing that rotates continuously when switch on - The cartridge are loaded by the operator so as to provide the data currently needed for the job in hand - Bach tracks is devided up into sectors(often or 8), sectors are read or written or more at a time as blocks by means of a read - There are usually one head for each surface, all the heads are moved - Sunchronously across the tracks - Once in position all the data on the equiradial tracks can be read or written without further movement of the heads - Cylinder is a set of equiradial tracks - A cartridge comprises several flat disks mounted on a central sprindle When mounted it rotates at a high speed enabling data to be read from or written to it The data is recorded magnetically on both surfaces of each disk in the form of concertric tracks .d o m o w w w d o C lic k to bu y bu to k lic C w w w N O W ! h a n g e Vi e N PD ! XC er O W F- w m h a n g e Vi e w PD XC er F- c u -tr a c k c y o c u -tr a c k c Certain models of disk units also have a number of fixed read/write heads in addition to the movable heads The fixed head are positioned permanently over certain of the outer tracks, there being one head per track, so climimating the need for head movement - The heads are very close disk surface - Curshion of air carried by the rotating disk Question Winchester disks( hard disks )? - Comprises a number of platters(disks) permanently into an airtight enclosure - All dust is excluded thus perimiting the read/write heads to be positioned even closer to the surfaces and so enabling greater recording densities to be employed - The disks have greater storage capacity and a higher rate of data transger - It has the lubricated surfaces allowing the heads “land” when the platters cease to rotate, so eliminating head crashes - Winchester platters are either 14 in, in, 5¼ in or 3½ in diameter Question Floppy disks? - Diskettes, generally called floppy disks, are single disks made of flexible plastic and permanently housed is an envelope - The data on floppy disks is in concentric tracks on the outer part of the surfaces and access to it is via slot in the envelope - The most common size are 3ẵ in, 5ẳin, and in diameter disks, the 3ẵ in disks have the advantages of a shutter - Floppy disks may be either single or double sided and of course the drive needs to be correspondingly equipped - Both the drives and the floppy disks themselves are inexpensive with the result that they have come into extensive used by small business and home computer buffs - The range of capacities is from 1/4 to megabytes and transfer rates around 125 to 250 kilobytes per seconds Question Optical disks? - Optical disk are comparatively new development for data storage - Optical disks consist of a single removable glass, plastic or metal disk coated on one side with tellurium and protected by a mm layer or transpacent plastic - The disk diameters are mostly between in and 14 in they rotate on a spindle in a similar fashion to magnetic disks - The data is recorded in the form of minute pits burned into the telliurium coating by a finely-focused lazer beam - Optical disks hold between 0.7 and GBs, this is about 20 times greater than magnetic dis cartridges - The data is read by a low power laser beam which moved across the surface and is reflected into a photo cell .d o m o w w w d o C lic k to bu y bu to k lic C w w w N O W ! h a n g e Vi e N PD ! XC er O W F- w m h a n g e Vi e w PD XC er F- c u -tr a c k c y o c u -tr a c k c - Optical disks rotate mostly at 1500 r.p.m which, allowing for the movement of the laser unti, given access time of between 16 & 500 ms and data transfer rates of 0.6 to MVs per second - The draw back of optical disks is that the data cannot be erased so making them non-rewriteable Question Mass storage media? - Mass storage media is a high capacity disk system as when necessary by transferring data from a number of “data cartridges” house in cells - Each cartridge consists of a in wide magnetic modium inside a protective cover - In order to load the disk system, the data cartridges are moved automatically from the cells - A typical system consists of 9440 cartridges giving a storage capacity of 472000 million bytes Question Magnetic drums? - A magnetic drum consists of a cylinder upon the surface of which data is stored in magnetic form in tracks running around its circumference, each track has its own read/write head - A typical magnetic drum has 800 tracks each capable of holding 5000 bytes Question Charge_coupled Device Memory (CCD)? - CCD consists of thousands tiny metal squares each capable of holding an electric charge, thus representing a bit - The squares are in the form of an array 64 x 64 holding 4096 bits - It is very impact - CCD is volate lity storage Question Magnetic Bubble Memory? - A thin wayer of magnetic garnet is capable of containing tiny domains or cylinders of magnetism, called bubbles - By erasing unwanted bubbles, the resultant presence of a bubbles represent a or a bit - The main ads are low power consumption, compactness, robustness reliability and non-volitility Question 10 Megnetic tape? - The magnetic tape usage is now more as a backup medium rather than a primary method of backing storage - It is often used as a depositony for disk dumped from fixed data storage - It is in reells of up 3600 feet and is made of Mylar plastic tape, 1/2 in wide and coated with a magnetic material on one side - The data is read from one read and written to another - A reel of tape is loaded on a magnetic tape drive, and so as many drives are needed as reels during a processing run - It is used as a backing medium than a primary method of backing storage - The seconds usually have to be sequence where store in magnetic tape Chapter 7: COMPUTER FILES Question File Processes? Sorting d o m o w w w d o C lic k to bu y bu to k lic C w w w N O W ! h a n g e Vi e N PD ! XC er O W F- w m h a n g e Vi e w PD XC er F- c u -tr a c k c ... set rapidly rotating on a print chain d Band printers - The band printer has rotating scalloped steel band e Drum printers - Are line printers, the print character are raised in bands around a... wires causes the ink from the ribbon to fuse to a piece of regular paper g Inl Jet Printers - The ink jet prints by using a small droplet generator to break special inks into tiny drops, which... lubricated surfaces allowing the heads “land” when the platters cease to rotate, so eliminating head crashes - Winchester platters are either 14 in, in, 5¼ in or 3½ in diameter Question Floppy