It controls the operation of all parts of computer. A CPU has 3 components as listed below. Think of the ALU as the logical part of the brain. The ALU thinks in bits i. It is made up of a group of memory locations built directly into the CPU called registers. These are used to hold the data binary information that are being processed by the current instruction. Primary memory is memory that is part of the computer itself and necessary for its functioning.
It consists of mainly two types of memories:. As soon as the machine is switched off, data is erased. RAM is volatile. Volatile means that the data stored in memory is lost when we switch off the computer or if there is a power failure.
There are different types of RAM available. Some of them are described below. The memory from which we can only read but cannot write on it.
This type of memory is non-volatile. The information is stored permanently in such memories during manufacture. A ROM, stores such instructions that are required to start a computer. This operation is referred to as bootstrap. The different types of ROM are given below. Floppy diskettes, hard disk, tapes and optical disks come under the category of external storage devices or ancillary storage devices.
A1: A computer network is a group of computers linked to each other that enables the computer to communicate with another computer and share their resources, data, and applications. It is used to connect two or more personal computers through a communication medium such as coaxial cable, twisted pair, etc.
LAN is not very costly as it is built with inexpensive hardware such as network adapters, hubs and ethernet cables. The data in Local Area Network will be transferred at an extremely faster rate. LAN provides higher security. It is a network arranged within a range of 10 meters, typically within an individual person. PAN is used for connecting the computer devices of personal use. Personal Area Network idea was bought by Thomas Zimmerman who was a research scientist.
The name of the bus or its operation usually implies the type of signal it carries or method of operation. All computers use three types of basic buses. The name of the bus is generally determined by the type of signal it is carrying or the method of operation. We group the buses into three areas as you see them in their most common uses.
They are as follows: I. Control bus II. Data bus III. Address bus Control Bus The control bus is used by the CPU to direct and monitor the actions of the other functional areas of the computer. It is used to transmit a variety of individual signals read, write, interrupt, acknowledge, and so forth necessary to control and coordinate the operations of the computer.
The individual signals transmitted over these buses carry control signal from ALU to memory and from memory to ALU and then to the output unit.
Address Bus The address bus consists of all the signals necessary to define any of the possible memory address locations within the computer, or for modular memories any of the possible memory address locations within a module. An address is defined as a label, symbol, or other set of characters used to designate a location or register where information is stored. The width of the address bus determines the amount of memory that can be addressed.
This explains the 4 GB memory restriction on bit operating systems. Data Bus The bidirectional data bus, sometimes called the memory bus, handles the transfer of all data and instructions between functional areas of the computer. The bidirectional data bus can only transmit in one direction at a time. The data bus is used to transfer instructions from memory to the CPU for execution.
It carries data operands to and from the CPU and memory as required by instruction translation. The information on the data bus is either written into The data bus is not limited to transferring data; it is also used to transfer program instructions. Discuss six roles of operating systems Without an operating system, a computer is little more than a bundle of plastic, metal, and a few bits of expensive silicon. Whereas most software runs on a computer, the operating system is the software that runs the computer.
Below are major roles of operating systems I. Provides a user interface: Facilitates easy communication between user and computer with interpretation of commands and instructions.
CLI requires the user to interact with operating system in the form of text keyed in from the keyboard. In this, the user has to learn and remember the different commands required for copying, deleting, opening a file or folder etc.
File management: the operating system manages reading and writing in the file system and the user and application file access authorizations. It keeps track of where all the files are on the computer. The file management system allows the user to perform such tasks as creating files and directories, renaming files, coping and moving files, and deleting files.
Also keeps track of where files are located on the hard drive through the type of file system. Management of the random access memory: the operating system is responsible for managing the memory space allocated to each application and, where relevant, to each user. Also responsible for managing all system memory which is currently in use by programs. This ensures that a program does not interfere with memory already in use by another program.
Since programs time share, each program must have independent access to memory. The activities of memory management handled by OS are— 1 allocate memory, 2 free memory, 3 re-allocate memory to a program when a used block is freed, and 4 keep track of memory usage.
Protection and Security— OS protects the resources of system. User authentication, file attributes like read, write, encryption, and back-up of data are used by OS to provide basic protection. The access of programs, processes, and users, to the resources defined by the computer are controlled by the protection mechanism.
Protection ensures that the resources of the computer are used in a consistent way. Security mechanism prevents unauthorized access to the computer. Security concerns include—security of software, security of data stored in the computer, and security of physical resources of the computer.
In a personal computer, security can be ensured using— 1 user accounts— individual accounts for each user, 2 user authentication—using password protection 3 access rights—define rights for access of different kind of information for different people, 4 data encryption—store data in computer in encrypted form, and 5 data backup—storing data on a peripheral device other than the hard disk.
In a networked environment, only trusted computers should be able to share data. Some of the common security threats occur due to hacking, viruses etc. Device Management— The device management tasks handled by OS are— 1 open, close and write device drivers, and 2 communicate, control and monitor the device driver. Several peripheral devices like mouse, hard disk, printer, plotter etc. The peripheral devices have varying characteristics like character or block device, sequential or random access device, and dedicated or shared device.
OS manages and controls the devices attached to the computer. OS provides appropriate functionality to the application programs for controlling different aspects of the devices. OS handles the devices by combining both hardware and software techniques. The device driver software comes along with each device. A device communicates with the computer hardware via a port for example, a serial port or a parallel port. Bus is a common set of wires used by one or more devices. A device controller operates a port, bus, and a device.
Device controller is just like a bridge between the device and the operating system. Device driver is the software with which the device controller communicates with the operating system. A process is a program in a state of execution. It is a unit of work for the operating system. A process can be created, executed, and stopped. In contrast, a program is always static and does not have any state. A program may have two or more processes running. A process and a program are, thus, two different entities.
The process management function of an operating system handles allocation of resources to the processes in an efficient manner. The allocation of resources required by a process is made during process creation and process execution. A process changes its state as it is executed.
A standard process describes the steps needed for processing to take place. The Fetch-Decode-Execute cycle of a computer is the process by which a computer: 1. This cycle is repeated continuously by the central processing unit CPU , from bootup to when the computer is shut down.
FECTH The first step the CPU carries out is to fetch some data and instructions program from main memory then store them in its own internal temporary memory areas. The CPU places the address of the next item to be fetched on to the address bus. Each make of CPU has different instruction set. Published in September 29th the book become immediate popular and critical acclaim in computer science, programming books. Physical Layer: digital transmission, multiplexing, transmission media.
Datagram networks. Data link layer: Introduction, Block coding, cyclic codes, chccksum, framing, flow and error control, Noiseless channels, noisy channels, HDLC, point to point protocols. Medium Access sub layer: Random access, controlled access, channelization. IEEE standards.
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