Understanding Computers: Hardware, Memory, and Software - Prof. Lila Ghemri, Study notes of Computer Science

Download Understanding Computers: Hardware, Memory, and Software - Prof. Lila Ghemri and more Study notes Computer Science in PDF only on Docsity! Overview of Computers What is a Computer? A computer is an electronic device that can store, retrieve and process data at speed millions or billions times faster than a human. Modern-day computers are categorized according to their size and performance. Microcomputers are the most common computers. They are used by a single person at a time, they are single user. The largest microcomputers are called workstations. Mini-computers or mainframes are used by research labs or businesses and are larger and faster than workstations. They are multi-user. Supercomputers are the most powerful mainframes computers. They are specialized computers used for high-speed computations. They are mostly used by the Army and NASA. A Computer System is composed of two major elements: hardware and software. The various devices that comprise a computer system are referred to as hardware. Hardware is the equipment used to perform computations The programs that run on a computer are called software. Software consists of the programs that enable us to use and solve problems with a computer. Computer Hardware: The major hardware components of a computer system are common to most computers and are: Main memory Secondary memory devices Central Processing Unit or CPU. Input devices Output devices The CPU, main memory, and secondary memory devices are usually contained in the systems unit. This rectangular box is sometimes called "the computer." The monitor is the TV-like screen. Memory Memory is an essential component of any computer. It is where the data and programs used by the computer are stored. In order to be able to use any piece of information, a computer must store it first. What is Memory? We can imagine the memory of a computer as an ordered sequence of storage locations called memory cells. To store and access information, the computer must have a way of identifying the individual memory cells. Therefore, each memory cell has a unique address that indicates its relative position in memory. Most computers have millions of individual memory cells, each with it own address. The data stored in a memory cell are called the content of the cell. Table below shows an example of a computer memory consisting of a 1000 cells with addresses from 0 to 999: Address Contents 0 -27.2 1 345 2 00.05 3 C 4 -26 5 H . . . . . . . . 998 X 999 56.900 Main Memory Secondary Memory Fast Slow Expensive Cheap Low Capacity Large capacity Connects directly to the processor Can't connect directly to the processor Newer Secondary Memory Devices: - Compact Disks (CD) - Flash Disks Central Processing Unit The central processing unit , CPU, or processor is the "brain" of the computer system. The CPU has two roles: coordinating and controlling all computer operations and performing arithmetic and logical operations. A particular computer will have a particular type of processor, or CPU such as a Pentium chip. (Integrated circuits are often called "chips.") The CPU is composed of three basic components: The registers, The ALU, The Control Unit. Registers: these components are special memory locations that can be accessed very fast. ALU: This component is the number cruncher of the CPU. The Arithmetic / Logic Unit performs all the mathematical calculations of the CPU. It is composed of complex circuitry. The ALU can add, subtract, multiply, divide, and perform a host of logical operations such as determining whether a number is larger than another. Control Unit: This component is responsible for directing the flow of instructions and data within the CPU. It works as process known as the fetch-decode-execute cycle. In each cycle, the Control Unit: 1. Fetches the next instruction of the program currently being executed. 2. Interprets the instruction to determine what should be done. 3. Executes the instruction Input and Output Devices Input and output devices allow the computer system to interact with the outside world by moving data into and out of the system. We used I/O devices to communicate with the computer. An input device is used to bring data into the system. Some input devices are: Keyboard Mouse Microphone Bar code reader An output device is used to send data out of the system. Some output devices are: Monitor Printer Speaker Input/output devices are usually called I/O devices. They are directly connected to an electronic module inside the systems unit called a device controller. For example, the speakers of a multimedia computer system are directly connected to a device controller called an audio card (such as a SoundBlaster), which in turn is connected to the rest of the system. Computer Software: Software consists of the programs that enable us to solve problems with a computer. The software that makes the computer friendly to the user and which is an integral part of every system is the Operating System. Operating System: The collection of computer programs that control the interaction of the user and the computer program is called operating system (OS). The operating system is responsible for directing all computer operations and managing all computer resources. Most Common OS by user interface type Command-Line Interface Graphical User Interface UNIX Macintosh OS MS-DOS Windows 95/98/NT/2000 VMS UNIX + X windows Systems An OS that uses a command-line interface displays a brief message called a prompt that indicates it is ready to receive input. The user then types a command at the keyboard. Some tasks that the operating system performs: 1. Communicate with the user: receive commands and execute them or reject them with an error message. 2. Manage memory, processor time and other resources 3. Collect input from input devices such as keyboard or mouse and provide it to the program being run. 4. Conveying program output to the screen, printer or other output devices 5. Access data from secondary storage 6. Write to secondary storage. 7. Verify that each user can only access or modify the data for which they have the proper authorization.