Backing storage is also called secondary storage external storage and auxiliary storage. Chapter 2: MICOPROCESSOR. Question 1. Cache Memory? - Cache memory is a small amount of very fast store with faster access time than the main memory. - Cache memory is used to temporaryty store data instructions that are likely to be retrieved many times, thus speeds up the processing of data. - Sits between main storage and the processor acting as holding area through which all data and instructions pass. - Old data in the cache memory is over written by new then cache is full. Question 2. Virtual Memory? - Virtual memory makes use of both the main memory and backing store. - In a virtual memory sys, each user has the illusion that his program is in the main memory all the time. - The sys maintains this illusion by keeping some of the “unused” portion of the program’s code and data on a backing store device which is usually magnetic disk - The movement of the unused portion from the backing store to the mian memory is transparent to the users. - Please refer to diagram for virtual memory. Backing Store Main Memory Virtual Memory Chapter 3: BATCH/ ONLINE AND REAL TIME PROCESSING SYSTEM. Question 1. Batch Processing System? A3 A1 A2 A2 A3 A1 - Def: Computer processing does not begin until all the input data has been collected and grouped together called Batched Generally data is accumulated for a certain period of time or unitl a certain quantity. - Ads: Response time is not critical. Need to process large volumn of data. Computer efficiency is more important than response time. - Dis: Time between recording and processing of source document is long Rereen normally required if errors are encountered. Data is not current. Error correction is more difficult. Question 2. 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 3. 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 1. Classification of printers? 1. 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 2. 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 3. Classifying printers according to print quality Kinds of quality printers Draft quality Near letter quality(NLQ) Letter quality Graphic quality Question 2. Describe some types of printer? 1. 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. - 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 3. Characteristics of a page printers? - Speed - Characters sets - Copies - Intelligence - Output Chapter 5: DATA STORAGE MEDIA. Question 1. 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 2. 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 4 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. Certain models of disk units also have a number of fixed read/write heads in addition to the movable heads. . Storage capacity: much enough - Interchangeability: can be change easily - Security: safe enough - Transfer rate: fast enough - Cost: economic Question 2. Magnetic disks? - This comprises. printers? - Speed - Characters sets - Copies - Intelligence - Output Chapter 5: DATA STORAGE MEDIA. Question 1. Data storage Requirements Characteristics? - Low access time: fast speed - Storage. 3. Classifying printers according to print quality Kinds of quality printers Draft quality Near letter quality(NLQ) Letter quality Graphic quality Question 2. Describe some types of printer?