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 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 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 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 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 Computer Computer Modem Modem 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 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 - 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 . memory placement policy: - First fit - Best fit - Worst fit 1. First fit policy, an incoming job is placed in the first available free space large enough to fit it. This allows the placement. 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. 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