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y o c u -tr a c k c Worst fit policy, an incoming job is placed in the largest possible hole of free space Question 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 Chapter 8: MEMORY MANAGEMENT Question 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 Types of network layout? Network topology is the name given to the various types of network layout Start network(or centralised network) - This network all communications go through a central node Node A Node D Central(Hub) active 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 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 Mesh network (or distributed network) - This network may be fully connected or partially connected A - E B D C - Data can get from one node to another node via different route - Multi point to point Ring network( or loop network) A D - Work stations connect to the ring - More cabling requiring than BUS - The connectors used with a lot of problem - Cable is used UTP, STP Bus network( or multidrop network) A B B C - 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 Network control? 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 Modems(modulation demodulation) A telephone line Modem Digital signal B modem analog signal OR Com pute Com Mod pute 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 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 Transmission a Simplex transmission Mod 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 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 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 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 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 - 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 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 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 Chapter 10: DATA COMMUNICATIONS Question Write a short note of? 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 Multiplexing is a means of combining together data from several sources so that it can be transmitted along one comminication line 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 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 Protocol is an “agreement” where by devices can communicate is a fully understand manner Multidrop line has several terminals on concentrator attached to it Distributed data processing sys is one of which interconnected points at which processing power and storage capacity are availble Question 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 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 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 ... subject in its own right, encompassing not only data transmission but also sound and video transmission via telephone lines, radio links and satellite links Multiplexing is a means of combining together... manner Multidrop line has several terminals on concentrator attached to it Distributed data processing sys is one of which interconnected points at which processing power and storage... 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