Download Operating System Thesis and more Lecture notes Operating Systems in PDF only on Docsity!
1. WHY SHOULD A COMPUTER SYSTEM BE AUDITED?
The reason computer system be audited is to determine weaknesses in the operating systems, check Computer fraud and abuse which are detrimental to the organisation. IT auditing takes that one step further and evaluates the controls around the information with respect to confidentiality, integrity, and availability
LIST AND BRIEFLY EXPLAIN THE THREE TYPES OF CONTROL
WHICH SYSTEM AUDIT SEAT TO CONFIRM
(a) General Controls Review: A review of the controls which govern the development, operation, maintenance, and security of application systems in a particular environment. This type of audit might involve reviewing a data center, an operating system, a security software tool, or processes and procedures (such as the procedure for controlling production program changes),
(b) Application Controls Review: A review of controls for a specific application system. This would involve an examination of the controls over the input, processing, and output of system data. Data communications issues, program and data security, system change control, and data quality issues are also considered.
(c) System Development Review: A review of the development of a new application system. This involves an evaluation of the development process as well as the product. Consideration is also given to the general controls over a new application, particularly if a new operating environment or technical platform will be used.
2. DESCRIBE IN BRIEF THE 4 FEATURES THAT ARE
INCORPORATED INTO MOST OPERATING SYSTEMS
(a) System Calls: A system call is a request by a computer program to the operating system's kernel. When a system call is invoked, control is transferred to the kernel which, in turn, determines whether the calling application should be granted the requested service. On modern microprocessors, there are at least two modes of operation: kernel mode and user mode. If an application running in user mode tries to perform a privileged operation (such as directly accessing the hardware), the CPU will most likely throw an exception. So, then, how does an application read input from the keyboard or write to the screen? It does so by sending a request to the kernel. Of course, this slows down the operation, but ensures that application programs do not execute code that could damage or compromise the system..
(b) Device drivers : A computer system is usually made up of several devices such as disk drives, keyboards, mice, video adapters, sound cards, etc. When a user attaches such devices to their computer, they expect the operating system to identify the device and make use of it. Indeed, the operating system may know what the device is but not how to communicate with it. The latter problem is solved by means of a driver. A device driver is a computer program that controls a particular device attached to a computer. It provides an interface through which the operating system can transparently make calls to the device. In fact, device drivers have built-in functions that are meant to be called by the operating system or other privileged programs.
(c) File system: Every computer file is stored in a linear space on a storage device of finite capacity. Each file has its address on storage, which is determined by the number of byte offsets from the beginning of the storage medium. But then, there is the need for a structure that tells where one piece of data begins and a where it ends—a file system. File systems keep track of unused space on the disk as well as additional
there is at most one process running on the system) while all the others are waiting their turn. The main idea of multiprogramming is to maximize the use of CPU time. Indeed, suppose the currently running process is performing an I/O task (which, by definition, does not need the CPU to be accomplished). Then, the OS may interrupt that process and give the control to one of the other in-main-memory programs that are ready to execute (i.e. process context switching). In this way, no CPU time is wasted by the system waiting for the I/O task to be completed, and a running process keeps executing until either it voluntarily releases the CPU or when it blocks for an I/O operation. Therefore, the ultimate goal of multiprogramming is to keep the CPU busy as long as there are processes ready to execute
(c) TIME SHARING: Time sharing system is where each process is allotted a particular time span and the process has to finish its completion within that time span. If it is failed to complete its execution then CPU control goes to the immediate next process. As the name itself suggests, in a time-sharing system or multi-tasking system, multiple jobs can be executed on a system at the same time by sharing the CPU time among them. It is considered to be a logical extension of multiprogramming because both does simultaneous execution but differ in their prime objectives. The main objective of time-sharing systems is to minimize response time but not maximizing the processor use(which is the objective of multiprogramming systems. They minimize the response time i.e; greater the response time, lesser is the efficiency of the system and reduce CPU idle time
(d) (^) REAL – TIME: A real-time operating system ( RTOS ) is an operating system (OS) intended to serve real-time applications that process data as it comes in, typically without buffer delays. Processing time requirements (including any OS delay) are measured in tenths of seconds or shorter increments of time. A real time system is a time bound system which has well defined fixed time constraints. Processing must be done within the defined constraints or the system will fail. They either are event driven or time sharing. Event driven systems switch
between tasks based on their priorities while time sharing systems switch the task based on clock interrupts
4. LIST AND BRIEFLY EXPLAIN 5 TYPES OF INTERRUPT
KNOWN TO YOU?
(a) The External Interrupt occurs when any Input and Output Device request for any Operation and the CPU will Execute that instructions first For Example When a Program is executed and when we move the Mouse on the Screen then the CPU will handle this External interrupt first and after that he will resume with his Operation.
(b) The Internal Interrupts are those which are occurred due to Some Problem in the Execution For Example when a user performing any Operation which contains any Error and which contains any type of Error. So that Internal Interrupts are those which are occurred by the Some Operations or by Some Instructions and the Operations those are not Possible but a user is trying for that Operation.
(c) (^) The Software Interrupts are those which are made some call to the System for Example while we are Processing Some Instructions and when we wants to Execute one more Application Program
(d) Maskable Interrupt : The hardware interrupts which can be delayed when a much highest priority interrupt has occurred to the processor.
(e) Non Maskable Interrupt : The hardware which cannot be delayed and should process by the processor immediately
9. DEFINE A SYSTEM-CALL AND STATE THE DIFFERENCE
BETWEEN SPOOLING AND BUFFERING
(a) A SYSTEM CALL is the interface between the operating system and the user programs.
(b) Spooling is a process in placing data in temporary working area for another program to process. Spooling is more efficient than buffering.
(c) BUFFERING : Buffer overlaps the I/O of one job with the computation of the same job temporarily. Buffering is less efficient than spooling.
- DEFINE SCHEDULING
Scheduling is the responsibility of determining how to allocate processor time among the processes. i.e it is the responsibility of
the o/s to determine the sequence and timing
11. LIST AND BRIEFLY EXPLAIN 6 SCHEDULING
ALGORITHM
(a) Maximization through put: i.e to service the highest numbers of jobs at a time.
(b) Fairness: To treat all processes the same.
(c) Predictability: A given job should run in about the same time regardless of the load.
(d) Balance resources use: All system resources should be kept busy.
(e) Avoidance of indefinite postponement: No jobs should be kept waiting indefinitely.
(f) Maximization: maximize the number of interactive users.
12. STATE 6 QUALITIES THAT YOU EXPECT TO FIND IN A
GOOD OPERATING SYSTEM
(a) It monitors system health and functionality.
(b) It provide structure fir data management
(c) It provides environment for software to operate.
(d) It coordinate hardware component.
(e) It provides interface between the user and the hardware.
(f) It gives room for other software to execute their programs
13. NAME AND EXPLAIN 3 MAIN ARCHITECTURE DRIVING
OPERATING SYSTEM
(a) NETWORK O/S : It is a collection of software and associated protocols that allow a set of autonomous computers which are inter-connected by a computer network to be used together in a convenient and cost effective manner.
(b) DISTRIBUTED O/S: This is a software over collection of independent, networked, communicating and physically separate computational nodes.
(c) MULTI-PROCESSOR O/S : This is an o/s where by multiple CPUs are connected into a single computer.
14. DESCRIBE 4 BASIC DEVICES THAT ARE EMPLOYED TO
CONNECT TWO OR MORE NETWORKS TOGETHER
(a) ROUTERS : This is used to connect devices together on within a LAN(local area network)
(b) SWITCHES : This connects devices together in an environment.
(c) HUBS : this is also a means of connecting devices together in order to share information.
16. WHAT IS DEADLOCK, EXPLAIN THE 4 CONDITION FOR
DEADLOCK TO OCCUR
A deadlock is a situation in which two computer programs sharing the same resource are effectively preventing each other from accessing the resource, resulting in both programs ceasing to function. The earliest computer operating systems ran only one program at a time.
Deadlock Conditions (a) MUTUAL EXCLUSION : The resources involved must be unshareable; otherwise, the processes would not be prevented from using the resource when necessary.
(b) HOLD AND WAIT OR PARTIAL ALLOCATION : The processes must hold the resources they have already been allocated while waiting for other (requested) resources. If the process had to release its resources when a new resource or resources were requested, deadlock could not occur because the process would not prevent others from using resources that it controlled.
(c) NO PRE-EMPTION : The processes must not have resources taken away while that resource is being used. Otherwise, deadlock could not occur since the operating system could simply take enough resources from running processes to enable any process to finish.
(d) RESOURCE WAITING OR CIRCULAR WAIT: A circular chain of processes, with each process holding resources which are currently being requested by the next process in the chain, cannot exist. If it does, the cycle theorem (which states that "a cycle in the resource graph is necessary for deadlock to occur") indicated that deadlock could occur.
17. DEFINE PROCESS AND ALSO EXPLAIN THE 4 PROCESS
STATE
A process is an instance of a program running in a computer. It is close in meaning to task , a term used in some operating systems. In UNIX and some other operating systems , a process is started when a program is initiated (either by a user entering a shell command or by another program).
FOUR PROCESS STATE
(i) Start : This is the initial state when a process is first started/created.
(ii) Ready : The process is waiting to be assigned to a processor. Ready processes are waiting to have the processor allocated to them by the operating system so that they can run. Process may come into this state after Start state or while running it by but interrupted by the scheduler to assign CPU to some other process
(iii) Running: Once the process has been assigned to a processor by the OS scheduler, the process state is set to running and the processor executes its instructions.
(iv) Waiting : Process moves into the waiting state if it needs to wait for a resource, such as waiting for user input, or waiting for a file to become available.
18. WHAT IS BUFFERING? GIVE 4 REASON WHY BUFFER
ARE NEEDED
Buffer : A buffer is a region of memory used to temporarily hold data while it is being moved from one place to another..
REASONS FOR BUFFER
a) Some device uses DMA(Direct Memory Address)therefore buffers are needed as the destination or source of the transfer.
