Computer system

y disks, are single disks made of flexible plastic and permanently housed is an envelope. 11 - 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 3½ in, 5¼in, and 8 in diameter disks, the 3½ 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 2 megabytes and transfer rates around 125 to 250 kilobytes per seconds. Question 5. 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 1 mm layer or transpacent plastic. - The disk diameters are mostly between 8 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. - 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 3 MVs per second. - The draw back of optical disks is that the data cannot be erased so making them non-rewriteable. Question 6. 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 3 in wide magnetic modium inside a protective cover 12 - 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 7. 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 8. 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 9. 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 1 or a 0 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. 13 - 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 1. File Processes? 1. Sorting a. The records in logical file are brought into some sequence as determined by key in the records. b. A computer is capable of sorting record into a “nested” sequence. c. Sorting is done by a “sorting generator”. This is part of the computer’s software and comprises several sophisticated sorting techniques that are called into use according to the file and the sort requirements. d. The need of sorting has dimished in line with the demise of magnetic tape as backing storage. 2. Merging - Merging implies that two or more files in the same sequence are combined into one file. a. File merging  Two or more separate files of similar seconds and in the same sequence are marged together so as to form one file. b. Record merging  The records from two or more “input” files, usually in the same sequence, are combined one record in the output file. 3. Matching a. Two or more input files (generally in the same sequence) are compared records against record in order to ensure that there is a complete set of records for each key. b. Masmatched records are highlighted for subsequent action 4. Summanizing a. Records with the same key in one file are accumulated together to form one record in the output file. b. Summanizing usually applies to a file presorted into a certain sequence and the resultant file is in the same sequence. 14 c. Records to be summarized are generally of a similar type. 5. Searching a. Searching is looking for records with certain keys or holding certain data and in some way making a note of these. b. An instance is a search for and count of all records with a debt balance of above a certain amount. 6. Information retrieval a. Information retrieval is the process that involves the bringing together of data from several files. b. Data may also be extracted from several files and combined before being presented as information. Chapter 8: DIRECT ACCESS FILE ORGANIZATION AND STRUCTURES. Question 1. Storage and Access Modes? There are 3 principal modes for storing and accessing accords on a disk or drum: 1. Serial mode: - The record are stored contigously regardless of their keys - The sole way of accessing serial seconds is to search through the complete file starting with the first record. - It is sometimes possible to partition a serial files thus reducing the search time by starting the search at the beginning of a known partition. - A serial file is normally of a temporary nature awaiting sorting into a useful sequence. 2. Sequential mode: - direct access sequential mode normally involves accessing sequential a file that is stored sequentially. - sequential mode is often associated with a master file held in a certain sequence and updated by a transaction file sorted into the same sequence. 3. Indexed_sequential/ selective_sequential mode - Indexed_sequential is a mode of storage where by records are held sequentially and accessed selectively. - Groups of unrequired records are skipped past. - Indexed sequential files may also be accessed haphazandly. 4. Random modes: 15 - Each record is stored in a location determind from the second’s key by means of an add generation algorithm. - The only erricient way to find a record is to use the algorithm - Random mode is applicable to master files  Ads of random modes  No index is required thus saving storage space  It is a fast access method because little or no searching is involved  Transaction do not need storing, thus saving time  New records are easily insertly into the random file provided they are not excessive in number  Dis  The main problem with the random mode is in achieving a uniform spread of records over the storage are allocated to the file Question 2. Direct Access Addressing? - The key of record is used to identify by record - The key of record also is used to decide its storage location(or address) 1. Self addressing: - Self addressing is a straight forwards method because a record’s address is equal to its key’s value - The file is inevitably stored in key sequence  Ads of self addressing  It leads directly to the wanted record  No indexing or searching is required  The key itself need not necessarily be held within the stored record- although it generally is  Dis  The storage space per second has to be the same  When records one missing, storage locations related to its must be left empty 2. Self addressing with key conversion - This method a basically similar to self addressing except that the key required a little processing to turn it into the record’s address - This leads to either a pricise address 16 3. Matrix addressing - In somes case, it is necessary to find the add of a record held within a multi dimensional matrix of record it’s called matrix addressing. Question 3. Direct Access Searching? - Where as addressing determines the location of a record by using algorithmic methods, searching finds the record by scanning groups of records, and index, or both. - ]The simplest method is to examine every record a file until the required record is found a shortcut is generally desiable. 1. Indexed sequential searching - A cylinder index is created to hold the highest cylinder’s key - Associated with each cylinder is a block index holding the highest key in each block within that cylinder - When searching for a record’s key in the index  The cylinder index is examined key_by_key until one is found that is larger than or equal to the wanted key this directs the search to the appropriate block index  The block index a similarly examined and the search  The block is searched record by record until the wanted record is found 2. Binary searching( binary chopping ) - The key in the index to be binary search must be in sequence and form a complete set - The search starts at the midpoint of the index and then moves half way to the left or right(down or up) depending upon whether are wanted key is less than or greater than the midpoint key - In pracice, the index is unlikely to as convenient as this example because it is not always possible to exactly halve each sucessive move(complete exact holvingis possible only when the total number of keys in the index is 20-1) - The average number of examinations comparisons is (log2k) -1 ( k is the number of keys in the index) 3. Block searching 17 - A block is a subdivision of an index. A block is devised to contain, roughly the square root of the number of keys in the whole index - The search is first through the block index to find the appropriate block and then through this to find the wanted key - The average number of examinations is square – root – k (k is the total number of keys) 4. Balanced binary tree searching - A binary tree is a relationship of keys such that the examination of any key leads to one of two other keys - The binary tree is actually in the form of an index containing all the keys together with a directory showing the braches stemming left and right from each key - Binary tree searching is suitable for an unsequenced file - The search is similar to binary searching in that each key examination holves the rinaining keys, on average Chapter 11: INTRODUCTION TO ARTIFICAL INTELLIGENCE. Question 1. AI? Atificial Intelligence It has three braches 1. Expert systems (or knowledge- base system) - ESs are programs that contain the knowledge of human expert, encoded so a computer can understand it with encated- knowledge seasoning machinism, ES can tackle problem that are beyond the seach of conventionally programmed computers. 2. Natural language systems (everyday native language) - Natural language systems are programs that understand the native language of the user, such as E - The most popular natural language systems are those that act as interfaces to data bases 3. Simple perception systems (for vision, speed and touch) - They can interpret visual scenes and decide if object meet inspection standards and quality control criteria, or move a robot to the proper location ot grasp a part for manufacturing Question 2. Who does the updates? 18 - Updating the knowledge bases is very diffirent when with updating databases because of the difference in the type of information and in the cause and effect relationship contained in knowledge bases - A knowledge in the area, when databases may be modified by a normal users Chapter 12: EXPERT SYSTEMS. Question 1. What is an ES( Expert system )? An ES is a knowledge-intersive program that solves a problem that normally requires human expertise  Characteristics of ESs - They solve problems as well as or better than human experts - They use knowledge in the form of rules or frames - They can consider multiple hypotheses simultaneouly  Types of ES - An assistant  Is the leasts expert or lowest level ESs  It helps a decision maker by doing routine analysis and porting out those portion of the work where human expertise is required - A colleage  The new discusses the problem until a joint decission is reached  When system is going wrong, the user adds more information to get it back on track - True ES  Is a system that advises the user without question  There are no practical areas today in which decission Question 2. A ES Life Cycle (ESLC)? - An accepted SDLC for expert systems has yet to be developed There are 6 phases life cycle in an ES 1. Phase1 – Selection of an Appropriate Problem - Phase 1 involves finding an appropriate problem for an ES, indentifying an expert to contribute the expertise - Establishing a preliminary approach 19 - Analysing the cost and benefitsPreparing a development plan 2. Phase 2 – Development of a prototype system - A prototype sys is a small version of an ES designed to test assumptions about how to encode the facts, the relationships and the knowledge of experts - The prototype permits the knowledge engineer to gain the expert’s commitment and to develop a deeper understanding of the field of expertise - Other subtasks in this phase:  Learning about the domain and the task  Specifying performance criteria  Selecting an ES building tool  Developing an implementation plan  Developing a detailed design for a complete system 3. Phase 3 – Development of a Complete System - The main work in this phase is the addition of a very large number of rules - The knowledge base has to be expanded to full knowledge base appropriate to the real world and the user interface has to be developed 4. Phase 4 – Evaluation of the system - This phase involves testing the system against the performance establised in earlier stages 5. Phase 5 – Intergration of the system - The ES has to be intergrated into the data flow and work patterns of the organization - In this stage, the expert system has to be interfaced with other databases, instruments and hardware. 6. Phase 6 – Maintenance of the system - The maintenance of the ES involves is updating, charging in the system when operating. When operating, more problems occur in the system, so it is necessary to continue take care the system by expert in a fix period of time - So expert system, are so complex that in a few year the maintenance costs will equal the development costs. 20 BOOK II: Computer systems architecture. Chapter 1 – 2: NUMBER BASES. Question 1. Common number bases used in computer hardware operation?  Decimal(denary) system: - The base is ten – there are 10 different symbols, the digits 0, 1, 2, etc...upto 9 - To represent value less than ten involves only one digit larger values need two or more digits  Binary system - The base must be two, with only the digits 0 and 1 available - To show values of two or ever require two or more binary digits  Octal system - Octal system has eight as its base, it uses the symbol 0, 1, 2 up to 7 only - Two or more digits are needed for values of eight and above  Hexadecimal system(hex) - Hexadecimal system has sixteen as its base, it use the symbols 0, 1, 2...,9 & A, B, C, D, E, F, to stand for the “digits” ten, eleven, twelve, thirteen, fourteen, fifteen. Question 2. Converting from Bases To Bases? 1. Change the decimal - Binary: Eg. (2559) 10 2559 1 1279 1 639 1 319 1 159 1 79 1 (2559)10 = (10111111111)2 39 1 19 1 9 1 4 0 2 1 21 0 0 - Octal: 7690 8 49 96,1 8 10 16 120 8 40 15 8 (7690)10 = (17012)8 - Hexadecimal: 6396 16 159 399 16 156 79 24 16 C F (6369)10 = (CF81)16 2. Convert to others from binary - To decimal (101010)2 (?)10 1.25 + 0.24 + 1.23 + 0.22 + 1.21 + 0.20 = 42 (101010)2 = (42)10 - To octal 100101101  1st step change into denary = 1.28 + 1.25 + 1.23 + 1.22 + 1.20 = 256 + 32 + 8 + 4 + 1 =(301)10  2nd step: convert to octal 2 1 0 7 1 12 15 8 1 1 22 301 8 61 37 8 (301)10 = (455)8 (100101101)2 = (455)8 - To hexadecimal 110111011011 1st step = 1.211 + 1.210 + 1.28 + 1.27 + 1.26 + 1.24 + 1.23 + 1.21 + 1.20 = 2048+ 1024 + 256 + 158 + 64 + 16 + 8 + 2 + 1 = (3547)10 2nd step 3547 16 384 221 16 27 61 (3547)10 = (CCA)16 (110111011011)2 = (CCA)16 3. Convert into binary and display the answer in normalized exponential form 247 1 123 1 61 1 30 1 15 1 7 1 3 1 1 1 0 1 (247)10 = (11110111)2 = 0. 1111011 x 2 normalized exponential form 5 5 4 11 13 13 23 Question 3. Integer and Floating – point arithmetic? 1. Floating – point Addition a. (0.1011 x 25 ) + (0.1001 x 25 ) = (0.1011 + 0. 1001) x 25 = 1.0100 x 25 = 0.10100 x 26 b. (0.1001 x 23 ) + (0.1110 x 25 ) = (0.001001 x 25 ) + (0.1110 x 25 ) = (0.001001 + 0.111000) x 25 = 1.000001 x 25 = 0.1000 x 26 (here have truncation) (0.1000001 x 26 ) 2. Floating – point subtraction a. (0.1110 x 27 ) – (0.1100 x 27 ) = 0.0010 x 27 = 0. 10 x 25 b. (0.1001 x 28 ) – ( 0.1000 x 25 ) = (0.1001 x 28 ) – ( 0.0001 x 28 ) = 0.1000 x 28 3. Floating – point multiplication a. (0.1010 x 23 ) x (0.1100 x 23 ) = (0.1010 x 0.1100) x 26 = 0.01111 x 26 = 0.1111 x 25 b. (0.11110 x 23 ) x ((0.01011) x 24 ) = (0.11110 x 0. 01011) x 27 = 0.001111 x 27 = 0.1111 x 25 4. Floating – point division. a. (0.11010 x 26) : (0.001 x 26) = (0.11010 x 26) : (1 x 23) = 0.1101 x 26 : 1x 23 = 0.1101 x 23 b. (0.110111 x 26) : (0.1001 x 24) = (0.110111 : 0.1001) x 22 = (1101.11 : 1001) x 22 = 1.100001 x 22 = 0.1100001 x 23 24 Chapter 3: TYPES OF INSTRUCTION AND ADDRESSING. Question 1. Types of instructions used in CS? 1. Arithmetic instructions. Arithmetic instructions include directives to the computers to perform additions, subtraction, multiplications, divisions and exponentiations. 2. Input/ output instructions. They direct the computer to read data values from the specified input devices into the main store for processing. They also include instructions to write the contents of memory locations holding the result of processing to a specified output device. 3. Decision or control instructions. Most data processing application will contain situations where alternative calculations or procedures will have to be executed based on the result of condition tests carried out. 4. Data handling instructions They include the copying of the content of one memory location to another or setting a memory locations to an initial value. Also include the management or insertion of characters into data items Examples of such instructions include branch instructions, jump instruction & stop instruction. Question 2. Types of addressing? 1. Direct addressing The operands of each machine instructions is used to retrieve the data 2. Indirect addressing The operands is used to specify the memory address which contains the address of the data to be processed Op – code OP – CODE OPERAND OP – CODE OPERAND 12345 Data item 25 12345 Data item Main storage Direct addressing Indirect addressing 3. Indexed addressing - The main applications of this type of addressing technique is to enable to access of sequential locations in memory that are adjacent to each other - Each adjcent memory address has value n+1, where n is the address of the previous location - When the first of the location have been accessed, the next memory location in sequence is accessed by simply increasing the add of the present location by 1 & using accessing it - The starting address of the series of locations is specified in the operand of the instruction - In order to access the next location in sequence, the content of the index register is increased by 1 a added to the opreand address - This is done repeatedly until the last memory location in the series is processed Indexed addressing. OP – CODE OPERAND Index Register Data 1 Data 2 Data 3 Data 4 26 Chapter 4: PROGRAMMING LANGUAGES. Question 1. Program and level of language? Program is group of constructions that is linked together to perform specific task. It’s necessary for a computer program to be written in a “PL” because at a computer program is created by a programing using a sys analyst’s specification of the job in the hand. 1. Machine language - ML is the set of bit(0,1) that can performed considered by CPU - Ads  fast  short prog  store in small memory - Dis  difficult to understand & remember its code  takes a lot of time to programming  difficult to use 2. Low level language - LLL is used to dercribe exactly procedure of performance of CPU at certain time - Features:  Instruction is written by natrural English or natural language  More powerful and so the prog is shortest  Need less instruction  Is a one to one relationship between the written instruction and the machine instructions  It’s instruction tend to be machine. It runs in OS - Ads:  Easy to write  Easy to understand  Known the processing data in CPU  Prog writing is shortset - Dis:  Must be complier 27  The time of running prog is longer than machine language 3. High level language - HLL was developed in order to further easy the work of programmers by making the programming language more procedure oriented - Features:  The statements of HLL are closer to natural english or other natural language  A HLL source program must be translated into machine code by means of a compiler or an interpreter - Ads:  Easy to wirte  Easy to understand  May be used for everybody  Closed to natural languages english language - Dis:  Must be interpreter by compiler or an interpreter before processing by the computer  The prog is long  The time to run the prog is longer than low level language Question 2. Some High Level Languages (HLL)? 1. COBOL: Common Business Oriented Language - COBOL is an exetensively used HLL and since around 1960 several versions have appeared - The original intention was that COBOL should be capable of being compiled and run on any model of computer - COBOL is now employed for many business data processing applications, and so a brief explaination of its structure follows - A COBOL program consists of 4 divisions:  Identifycation division this identifies the prog  Enviroment division specifies the computer to be used for compiling and processing  Data division specifies the format and relates to these to the names used in the procedure division 28  Procedure division comprises the statements in the source program, this is the main part of a COBOL program 2. BASIC: Beginners ALL purpose Symbolic Instruction Code - BASIC is a straightforward HLL intended for use in a time- sharing environment in this respect it is particularly beneficial in educational institutions - One of the difficulties with BASIC is the welter of dialects currently in use - Essentially BASIC consists of statements made up of verbs & variables. The verbs are similar to those in COBOL but there is a large to them that in effect become the addresses of their locations in the main store - A variable name must be unique and generally consists of one or a few alphabetic characters, purhaps followed by a digit 3. PASCAL: named after the famous 17th century French mathematician - It was expressly designed as a language to make programming more systematic and discriplired and in these respects lends itself to structured programming - It is however more difficult to learn than are COBOLS BASIC and so is unliked to be accepted as a language for microcomputers are geared to BASIC only Question 3. Operating Systeim? - Concept of OS:  An OS consists of a suite of programs, one of which, the master, kernel or exeactive program, remains resident in the main store. This program controls the other OS programs in th suites and between them they controls the application programs  Often the operating system includes various application packages among its suit of programs. Ex of such software include: word processing, electronic mail, networking, speadsheet, graphics and file handling - Function of OS 29  Pricrity assignment: Jobs waiting execution are scheduled according to either a predetermined or a dynamic assignments plan  Control of multiprogramming Control of accomplish multiprogramming an “executive” or “supervisor” program is employed to control the application programs  Communication Control of data transmission between terminals and the computer, and computer to computer  Database Control of DBMS  Software control Control of assemblers, compilers, utility software, and subroutines so that these are imediately available when required  Spooling The control of input/output peripherals in order to achieve their best utilisation  Dynamic allocation Of main and backing storage, including virtual storage  Operating allocation Via the console printer or VDU  Debugging and editing new programs In confunction with the compiler, and passing error msgs to the user  Operation log Maintaince of details of all jobs carried out by the computer  Application package control Especially with microcomputers, as describe above Chapter 6: TRANSLATORS. Question 1. Translators? 1. Assemblers  Def: A program that translates assembly language into machine code. Dos machine instruction is generated for each source instruction - The resulting program ran only be executed when the assembly process is completed 30  Operation: - Translates mnemonic operation codes into machine code & symbolic address into machine address - Includes the neressary linkages for closed subroutines and inserts appropriate machine code for macros - Allocates area of storage - Detects and indicates valid source language instruction - Procedures the object program on tape or disk required - The lesting may also include error codes if appropriate. To illustrate the methods used just think about an assembly program. We must first look at the directives  A directive is used to control the assembly process, it is not asembled but is obeyed by the assembler when it is encouteded, e.g ”END”, is sometimes called a pseudo-operation code on pseudo-opcode 2. Interpreter A program which translates and executes each source statement in logical sequence as the program one instruction at a time, completely translating and executing each instruction before it goes onto the next - Interpreter, which deals with the source program one instruction at a time, completely translating and executing each instruction before it goes onto the next - Interpreter seldom produce object code but call upon inbuilt routines instead - Some intermediate code is usually produced tempororily - If an interpreter is used, the source program will be translated every time the program is executed - Interpreters are widely used, particular for the programming language Basic on small computers  Interpriter are used for such things as: - Handling user commands in an interactive sys - Debugging programs as they run - Handling software produced for or by a different computer 3. Compilers: 31 A program that translates HLL into a machine orientated language, often the machine code. Many machine instructions are generated for each source statement - The compiler:  Translates the source program statements into machine code  Includes linkage for closed subroutines  Allcocates areas of main storage  Generates the object program on cards, tape and disc as required  Produces a printed listing of the source and objected programs when required  Tabulates a lish of errors found during compilation - Compilers are commonly used for the translation of HLL program - Compiler translates the whole of the HLL source program into a machine code object program prior to the program being loaded into main memory and executed - If a compiler is used, the same program need only be translated once  Stages of compilation  lexical analysis  systatical analysis  code generation Chapter 7: SOFTWARE. Question 1. Application software? - Application software comprises the programs that are written specifically to achieve resulting appertaining to the company’s activities - Application software comes from two source  They produce by themselves  Buy from an external agency 1. Ads and dis of using application packages in house  Ads - The requirements of the application are more easily met - There is more control in testing and debugging 32 - The more control over the usage and support obtained  Dis - There is a waiting period before the application can be implemented - Development cost is higher than buying a package 2. Ads and dis of using application package  Ads: - The packages can be used immediately - Documentation is generally good - It can be used on a varisty of machines - It is cheaper as the costs of the packages are shared between many users - Comprehensive on line help information and guided tutorials available - Easily remembered command syntax - Can be used in confunction with other software in an integrated fashion  Dis: - Modifications may be difficult for some applications - Package may be two generalized to suit user needs - Some features purchased may not be required - Support given depends on stability and professionalison of the vendor - User are required to comply with the owner’s regulations Question 2. Utility software? - Certain processing is common to a high proportion of computer users, and so utility software has been created to cater for this need - Utility software is intended to be sufficiently flexible to meet most user’s requirements and is tailored to meet their precise needs by means of parameter entered prior to use - Some of the utility programs described below may be incorporated into the OS that is used with a particular computer  File conversion: this convers the transference of data from any medium to any other 33  File copying: an exact copy of a data set is made on to another lot for the same type of storage medium  File reorganisation: direct access, files over flow records are stored in designed blocked, this is acceptable up to a point but from time it si necessary to reorganise the file so as to remove the overflow  File maintenance(amendment): this procedure involves the straightforward insertion and deletion of records into or form sequential files  Sorting: is frequently necessary in order to arrange a set of records into a certain sequence based on their key values  Dumping routines: a dump routine is used in confunction with a restfirt program ...  House keeping operations: there are programs or parts of a programs not directly concerned with the solution of the problem in hand  Trace routines: these entails, the dumping, display or printing of th program or other contents of the main store during program testing to facilitate error detection - Utilitys are commonly used to perform these functions:  Copying of files  Sorting of data  Merging of files  Data recovery  Reformating of records by reamanging their fields  File reorganization  Reporting of sys status and usages Question 3. System software? There are three main types of memory placement policy: - First fit - Best fit - Worst fit 34 1. First fit policy, an incoming job is placed in the first available free space large enough to fit it. This allows the placement decision to be made quickly 2. Best fit policy, an incoming job is placed in the free space in which it fits most tightly 3. Worst fit policy, an incoming job is placed in the largest possible hole of free space Question 4. Types of scheduling? - Scheduling of job is also an important part of any OS. It involves keeping track of and deciding which job is to be executed - Types of scheduling  Deadline scheduling  First in first out scheduling(FIFO)  Round robin scheduling  Shortest job first(STF) scheduling  Shortest remaining time scheduling(SRT) - More details about types of scheduling  In deadline scheduling certains are scheduled to be completed by a specifir time or deadline. Deadline scheduling can be very complex requiring substantial overhead in resource management  FIFO scheduling: processes are dispatched according to their arrival time in the ready queue. This type of  Round robin scheduling is similar to FIFO scheduling but the difference lies in that each job is given a slice of CPU time  SJF scheduling: shorter jobs are more favoured than longer one. SJF selects job that ensures the next jobs will complete & leave the sys as soon as possible  SRT scheduling: the job will the smallest estimated remaining run time is executed first. In SRT, a running job may be replaced by a new job with a shorter estimated run time 35 Chapter 8: MEMORY MANAGEMENT. Question 1. Virtual Storage System? - Instructions and data not currently needed might even be stored on the disk and thus free up a portion memory - Virtual storage systems have evolved to meet these needs. Virtual storage systems allow programs to be as large as necessary, even larger that the physical storage capacity of the computer - Translating the user’s view of the program into the physical reality of computer storage is one of the major task performed by virtual memory OS like IBM’s MVS and digital VMS - Virtual storage system included non paged systems Paged systems Chapter 9: NETWORKING. Question 1. Types of network layout? Network topology is the name given to the various types of network layout 1. Start network(or centralised network) - This network all communications go through a central node Node A Node D Central(Hub) active Passtive Node C Node B - The centra of star network is the hub which performs the function of routing msgs and data within the network - The hub manages & senvices all incoming and outgoing communication traffic. It’s also provide info services from a large central data bases 2. Mesh network (or distributed network) - This network may be fully connected or partially connected A E B 36 D C - Data can get from one node to another node via different route - Multi point to point 3. Ring network( or loop network) A B D C - Work stations connect to the ring - More cabling requiring than BUS - The connectors used with a lot of problem - Cable is used UTP, STP 4. Bus network( or multidrop network) A B - All workstations are connected the same cable segment - Commonly used for implomenting ethenet at 10 mbps(Mb/s) - The cable is terminalled at each end - Writing is normally store point to point - A faulty cable or work station will take the entire LAN down Question 2. Network control? 1. Modems(modulation demodulation) A telephone line B Modem modem 37 Digital signal analog signal OR Data transmission Using a Modem - To communicate between computers via telephone line, there is a need to convert signals from the computer into a form suitable for transmission over the telephone line or convert from digital signals into analogue signals, and convert back from analogue signals to digital signals - From source: digitals signals are converted into analogue signals(modulation) - At the received end analogue signals are converted back into digital signals (demodulation) - A device to handle modulation, demodulation process is called Modem 2. Bandwidth and Fibre Opties The major benefits of fibre opties are: - Fibre optic cables are much lighter and smaller in size - Greatly increased speed in data transmission - Greatly reliability - Greater secerity as lines can not be tapped 3. Transmission a. Simplex transmission This method allows for transmission in one direction only b. Half duplex transmission This method means that’s data can be transmitted in both directions, but is only on direction at a time c. Full duplex trasmission This method of transimission allows for transmission in both directions simultaneously * Two modes of transmission are used when transmitting data over communication lines. They are  asynchrorous Computer Computer Modem Modem 38  synchronous Asynchronous: - One character at a time is transmitted or received - Each character is preceded by a start bit and a stop bit  The start bit is used to indicate or character is being sent  The stop bit is used to indicate the end of the character - Asynchronous transmission is used for low speed devices Direction of transmission S S S S T T T T A 11000001 O 1111111 A 11000010 O R P R P T T Synchronous: - The speed of transmission is much faster - Transmission groups of character can be send down the line without the start and stop bits Direction of transmission 000111000001011100000011 Question 3. LAN_Local Area Networks?  Def: A LAN is a communication network in that connects office equipment to provide a variety of data communication service which features high transmission rates and low error rates  Characteristics: - Utilisation of some type of switching topology - Locality restricted to a few miles or in the same bulding - Proprietorship by a single organisation  Features: - LAN is after used in offices & it connects of fire equipment to provide a variety of data communication. Service with light transmission rate and low errors rate 39 - The majorities of LANs are connected by coxial cable, and the protocol(rule for communication) is very simple  Three other important aspects of LANs: - Acess method (protocol) Central control CSMA_CD Empty slot access Token access/token passing  LAN transmission modes: There are 2 main types of LAN transmission modes a. Baseband transmission: is essentially & binary method, each bit being represented by one of two states of an electric pulse passing through the network. Baseband is nevertheless suitable for most LANs, and is the mode employed by Ethernet and Cambridge Ring network b. Broadband transmission: the data is modulates into a carrier wave. Broadband transmission has a much greater band width than baseband, it can transmit sth like ten times as much in a given time  LAN is one of the distributed processing designs - LAN are considered loosely coupled system processors are located in separate machines and communicate at relatively low speeds - LAN is the means by which distribution takes places, regardless of what are distributed Chapter 10: DATA COMMUNICATIONS. Question 1. Write a short note of? 1. Communication is an extensive subject in its own right, encompassing not only data transmission but also sound and video transmission via telephone lines, radio links and satellite links. 2. Multiplexing is a means of combining together data from several sources so that it can be transmitted along one comminication line 3. Front – end processing: A front – end processor is usually a minicomputer or a microcomputer interposed between the main computer and the multiplexor Its purpose is to relieve the host computer from the bunden of communications housekeeping 40 4. Concentrators are device used to gather the bit from each terminal or group of terminal and hold them on buffer store unit until there are sufficient to justify forward transmission 5. Protocol is an “agreement” where by devices can communicate is a fully understand manner 6. Multidrop line has several terminals on concentrator attached to it 7. Distributed data processing sys is one of which interconnected points at which processing power and storage capacity are availble Question 2. Fibre Optics?  Fibre optics is that data and other information is transmitted in the form of light through very fine glass fibres  Ads: - High bandwidth eg data transmission capacity - Low cross – talk eg interference between adjacent fibres - Low attenuation eg loss of signal strength - Freedom from interference from external electrical and electromagnetic equipment - High reliability - Safe because no heat, sparks or electrical voltages are created - Economic because glass is loss expensive than copper Chapter 11: DISTRIBUTED PROCESSING. Question 1. Client/ Server Model? - It’s common way to employ distributed processing that is client/server architecture which splits into components - Server store & main palates the actual data & provide secenity, losting function transaction logging recovery capabilities - Client/ server model seems like PC lan each server support more users - Data request in form of SQL(structure quenf language) command travel across the network from client to server Client Server Database Request LAN Response 41 Question 2. File sharing VS client server? Network Client Server The file sharing model > Network Interface Interface The client/ server model File sharing - File are shared for a lot of machines in the network(each machine can Client server - Database are stored in the server machines and client machines can send Application tool process Application tool process Database Application tool process Database engine process Database Database engine process SQL execute commands 42 access to the shared files) - It can create heavy network traffic(each access to a large file can potentially block of the file, showing the system amount of information temporarily unavailable to other user) request for appropriate data - Only the records matching the request criteria raresent back to client machines so the sys never has heavy traffic Question 3. Distributed Database Topology? - With distributed processing system, user can access data, that is located among a number of physically separate servers. It provides user with a globol view of the data. - With distributed database, the problems with implementing still exists. - Developing distributed database application requires extensive planning to anticipate the many complex possibilities. - For a large number of transactions travelling across the network the capacity of communication lines and the possible impact a system must be carefully considered. Chapter 12: THE TCP/IP PROTOCOL SUITE. Question 1. The OSI model? - OSI model, adopted in 1983 by IOS <International Organization Standardization>, which is a framework for defining standards for linking hetenogenerous computer - The communication function are pastitioned into a vertical set of layers. Each layer performs are lated subset of the functions required to communicate with other sys - The OSI layers  Physical: concerned with transmission of unstructured bit stream over physical medium, deals with the mechinical, electrical, functional, and procedual characteristrics to access the physical medium  Data link: provides for the reliable transfer of information across the physical link, send blocks of data with the necessary synchronization, error control, and flow control. 43  Network: provides upper layers with independence from the data transmission and switching technologies used to connect systems, responsible for establishing, maintaining and terminating connections  Transport: provides rediable, transparent transfer of data between end points, provide end_to_end error recovery and flow control.  Session: provides the control structure for communicaton between applications, establishes, manages, and terminates connections between cooperating applications.  Presentation: provide independence to the application processes from difference in data representation(syntax)  Application: provide access to the OSI environment for users and also propvides distributed information services User oriented Application Users of transport Presentation service End to end Session connection oriented Transport Network Point to point Data link Network service link oriented Physical Perspectives on the OSI architecture Question 2. Protocols? Both OSI and the TCP/IP protocol suite deal with communications among hetrnogenerous computers Both are based on the concept of protocol and have many similarities a. TCP/IP protocol architecture TCP: Transmission Control Protocol IP: Internet Protocol - The TCP/IP protocol architecture is based on a view of communication that involves three agents: processes, hosts, and networks - Communication between processes takes place across networks to which the hosts are attached 44 - A network need only be concerned with routing data between hosts, as long as the hosts agree how to direct data to processes - It is natural to organize protocols into four layer i. Network access layer: contains those protocols that provide access to a communication network ii. Internet layer consists of the procedures required to allow data to traverse multiple networks between hosts iii. Host_host layer: containts protocol entities with the ability to deliver data between two processes on different host computers iv. Process/ application layer: contains protocols for resource sharing and remote access b. Operation of TCP/IP Application Application TCP TCP OS IP OS IP Network access protocol 1 Network access protocol 2 Network 1 Network 2 Netwo Communications using the TCP/ IP protocol architecture NAP: Network Access Points - IP is implemented in all of the end systems it keeps track of blocks of data to ensure that all are delivered veritably to the appropriate application - For successful communication, every entity in the over all sys must have a unique address, two level of addressing are needed  Global Internet Address(for communication)  Ports(for service) Try your best, you will get the best! IP NAP 1 NAP2 45 Contents BOOK I: Computer system fundamentals. CHAPTER 1 INTRODUCTION TO COMPUTER ................................ 2 CHAPTER 2 MICROPROCESSOR ........................................................ 3 CHAPTER 3 BATCH/ ONLINE AND REAL TIME PROCESSING SYSTEM ....................................................................................................... 4 46 CHAPTER 4 PRINTERS AND TERMINALS ....................................... 5 CHAPTER 5 DATA STORAGE MEDIA ............................................... 7 CHAPTER 7 COMPUTER FILES ........................................................... 9 CHAPTER 8 DIRECT ACCESS FILE ORGANIZATION AND STRUCTURES ........................................................................................... 10 CHAPTER 11 INTRODUCTION TO ARTIFICIAL INTELLIGENCE12 CHAPTER 12 EXPERT SYSTEMS ........................................................ 12 BOOK II: Computer systems architecture. CHAPTER 1 NUMBER BASES ............................................................ 13 CHAPTER 2 NUMBER BASES ............................................................ 13 CHAPTER 3 TYPES OF INSTRUCTION AND ADDRESSING ....... 16 CHAPTER 4 PROGRAMMING LANGUAGES ................................. 18 CHAPTER 6 TRANSLATORS .............................................................. 20 CHAPTER 7 SOFTWARE ..................................................................... 21 CHAPTER 8 MEMORY MANAGEMENT ......................................... 23 CHAPTER 9 NETWORKING ............................................................... 23 CHAPTER 10 DATA COMMUNICATION........................................... 26 CHAPTER 11 DISTRIBUTED PROCESSING ....................................... 27 CHAPTER 12 THE TCP/IP PROTOCOL SUITE................................... 28