Understanding Computer Systems: Processors, Storage, I/O Units, and More, Study notes of Information Systems

Download Understanding Computer Systems: Processors, Storage, I/O Units, and More and more Study notes Information Systems in PDF only on Docsity! ORGANIZATION OF COMPUTER SYSTEMS  CHAPTER THREE : Computer System Objective:  What a computer system is and how it works to process data 3.1. Introduction System is a group of components, consisting of subsystems or procedures that work in a coordination fashion to achieve some objective. A Computer System is composed of components that are classified either as Computer hardware or Computer software. 3.2. Computer Hardware Computer architecture is defined as the science of selecting and interconnecting hardware components to create computers that meet functional, performance, and cost goals. It can be described as the logical structure of the computer system. Computer hardware is the physical part of the computer that can be touched, seen, broken. What a computer in general does is, that  It takes input (in various forms)  Process it (according to a given set of instructions) and  Produce an output (in required form).  Store the information Based on this the hardware part of a computer system is composed of a number of interacting physical parts. The different hardware parts of a computer which are responsible for these operations are illustrated by the following model. Page 1 ORGANIZATION OF COMPUTER SYSTEMS Fig 3.1 Information flow in the computer hardware 3.2.1. The Central Processing Unit (CPU) The CPU or the microprocessor (or simply processor) is referred as the brain of the computer system; it is a VLSI chip inside the system, plugged onto the motherboard. A processor controls all internal and external devices, and performs arithmetic and logical operations. It is the most costly and main component of the computer system. A processor operates only on binary data, that is, data composed of 1s and 0s. These 1s and 0s correspond to electrical switches being switched ON or switched OFF. The processor performs, supervises, and controls the arithmetic and logic functions. It performs arithmetic operations such as additions, multiplication, division, and logical operations such as ‘is A greater than B’? The functions of a processor can be summed up as:  Carrying out arithmetic and logical operations Page 2 Secondary Storage Unit Input Unit Output Unit Control Unit (CU) Arithmetic Logical Unit (ALU) Registers Central Processing Unit Primary Memory Read Only Memory (ROM) Random Access Memory (RAM) ORGANIZATION OF COMPUTER SYSTEMS fetched from the sequence and executed, and so on. This type of instruction sequencing is possible only if there is a counter to calculate the address of the instruction after instruction. This counter is a register, which stores intermediate data used during the execution of the instructions after it is read from the memory. The important registers within the CPU are: Register Name Function Program Counter (PC) A program counter keeps track of next instruction to be executed Instruction Register (IR) Holds the instruction to be decoded by the control unit Memory Address Register (MAR) Holds address of the next location in memory to be accessed Memory Buffer Register (MBR) Is used for storing data either coming to the CPU or data being transferred by the CPU Accumulator (ACC) It is a general-purpose register used for storing temporary results and results produced by arithmetic logic unit Data Register (DR) Is used for storing the operands and other data.  CPU Characteristics 1. Machine Cycle time  The time in which a machine cycle occurs is measured in fractions of seconds. The machine cycle time ranges from milliseconds to Pico seconds. Machine cycle time can also be measured in terms of how many instruction are executed in one second usually millions of instructions per second (MIPS) 2. Clock Speed  CPU produces a series of electronic pulses at a predetermined rate, called clock Speed, which affects machine cycle time. System clock is a circuit that generates electronic pulses at a fixed rate to synchronize processing activities. Page 5 ORGANIZATION OF COMPUTER SYSTEMS  One cycle or pulse is known as a hertz (HZ). Normally, megahertz (MHZ) or giga hertz (GHZ) is the measurement of cycles in millions per second. 3. World Length and Bus Line Width  Data is moved in computer system in groups of bits. A bit is a Binary digit 0 or 1.  The number of bits the CPU can process at one time, called the word length of the CPU, determines overall system performance.  A CPU with word length of 32 (called 32 bit CPU) will process 32 bits of data in one machine cycle.  Data is transferred from the CPU to the other system components or vice versa via Bus Line.  Bus line is the physical wiring that connects the computer system components and transfers data between them. The number of bit a bus line can transfer at any one time is the bus line width. Page 6 ORGANIZATION OF COMPUTER SYSTEMS 3.2.2. Storage Units Storage units are used to store data. There are two types of storage units: Primary and Secondary. 3.2.2.1.Primary Storage The primary memory or the main memory is part of the main computer system. The processor directly stores and retrieves information from it. The processor accesses the main memory in random fashion, that is, the processor can access any location of this memory either to read information from it or store information in it. The primary memory is implemented by two types of memory technologies. The first is called Random Access Memory (RAM) and the other is Read Only Memory (ROM). 3.2.2.1.1. Random Access Memory (RAM) RAM can be defined as a block of sequential memory locations, each of which has a unique address determining the location and those locations contain a data element. It stores programs and data that are in active use. Storage locations in main memory are addressed directly by the CPU’s instructions. It is volatile in nature, which means the information stored in it remains as long as the power is switched ON. As soon as the power is switched OFF, the information contained in it vanishes. RAM can be further divided into two categories: 1. Dynamic RAM (DRAM): - This type of RAM holds the data in dynamic manner with the help of a refresh circuitry. Each second or even less than Page 7 ORGANIZATION OF COMPUTER SYSTEMS programmed in blocks. It is often used to hold control code such as the BIOS in a personal computer. It is used in Digital cellular phones, digital cameras, LAN switches, PC Cards for notebook computers, digital set-up boxes, embedded controllers, and other devices. 3.2.2.2. Secondary Storage units Secondary Storage: - Secondary storage or auxiliary storage, can take many forms, which have traditionally included punched cards, papers tape, magnetic tape, magnetic disk, floppies, and CD-ROMs. The information in the secondary storage device can be accessed, depending upon how the information is stored on the storage medium. Primarily, there are two methods of accessing data from the secondary storage devices:  Sequential: - Sequential access means the computer system must search the storage device from the beginning until it finds the required piece of data. The most common sequential access storage device would be a magnetic tape where data is stored sequentially and can be processed only sequentially. This access method is less expensive than other methods. The disadvantage of sequential organization is that searching for data is slow.  Direct: - Direct access, also known as random access, means that the computer can go directly to the information that the user wants. The most common direct access storage is the disk and the most popular types of disks today are magnetic and optical disks. 3.2.2.2.1. Sequential Access Media  Punched Cards Punched cards are one of the oldest and most familiar forms of data storage. There are two types of punched cards, 80 – columns, and 96 – columns and the first one is a standard punched card. Using one card we can represent 80 Page 10 ORGANIZATION OF COMPUTER SYSTEMS characters.  If only a numeric punch is in any column, it represents whatever number is punched out.  Punched Paper Tape Punched paper tape is a continuous strip of paper used to store data in much the same manner as punched cards. The paper tape is approximately one inch wide & can have either six or eight channels. Eight channels paper tape is based on the ASCII code. This storage media is less expensive and more compact than punched cards.  Magnetic Tapes Magnetic tapes are a particularly popular form of secondary storage because of their high data density (the number of bytes of instruction per inch of tape) and their convenience in handling. Magnetic tapes are approximately one - half inch wide and are made of Mylar – based plastic film which can be magnetized. Data are stored on a magnetic tape by running the tape over the electromagnetic called read/write head which magnetizes small spots on the tape. Seven-track tapes store information as bytes of information, where each byte consists of a six-bit code and a one-bit parity bit. Nine-track tape uses an eight-bit and a parity bit. An 800 bytes per inch density of magnetic tape and has a length of 100 inch can store 80,000 bytes of information. 3.2.2.2.2. Direct (Random) Access Media  Magnetic disks Magnetic disks are metals or plastic platters coated with ferrous oxide, an easily magnetizable material. Magnetic disks allow for random access of information Page 11 ORGANIZATION OF COMPUTER SYSTEMS and overcome the slow access time commonly found in tape files.  Floppy disks  Also called diskette.  Used to store programs and data for a longer period outside the computer system.  Often used with mini and micro computers.  Data is stored in concentric circles called tracks.  Each track is further divided into sectors  A sector stores the amount of information that can be read or written in single operation. Disk drive: - is part of a computer system which reads from and writes data on a disk.  Hard Disk  A high capacity magnetic disk made up of metal which can be fixed in the system unit of the computer.  Serves as a secondary storage.  Enables very fast accessibility of data.  Accessing data from hard disk is faster than from floppy disks.  The disks, which are usually grouped together into a disk pack, are separated by small air spaces to allow access for read/write head.  Each disk has approximately 200 tracks on which information is stored. Tracks of the small number on all adjacent disks are referred to as a Page 12 ORGANIZATION OF COMPUTER SYSTEMS c. Projectors  Hard Copy Output Devices A. Printers The most common output device you will encounter will be the printer. Printer is available in various forms, to suit the needs of various types of users. A printer is an output device that prints characters, symbols, and perhaps graphics on paper hardcopy. Printers are categorized according to whether or not the image produced is formed by physical contact of the print mechanism with the paper. Hence they classified as impact and non-impact printers. Impact printers have contact; non- impact printers do not. 1. Impact Printers These types of printers form images by striking a mechanism such as a print hammer or wheel against an inked ribbon, leaving an image on paper like a typewriter. Impact printers are dying out, though you might still run across a dot-matrix printer. Characteristics of Impact printers:  There is physical contact with the paper to produce an image  Relatively low consumable(ink, ribbon, etc) costs  Useful for bulky printing  Very noisy  Since they are mechanical in nature, they tend to slow Impact printers include:  Dot matrix Printers  Daisy Wheel Printers Page 15 ORGANIZATION OF COMPUTER SYSTEMS  Drum Printers  Dot matrix printer  It is the oldest printing technology and it prints one character at a time.  It can print any shape of character, which a user can specify.  The speed of dot matrix printers is measured in characters per second (cps). The speed can vary from about 200 to over 500 cps.  The print quality is determined by the number of pins (the mechanisms that print the dots), which can vary from 9 to 24.  Most dot matrix printers have a resolution ranging from 72 – 360 dpi (dot per inch).  Dot matrix printers are inexpensive and have low operating costs.  The major limitation of dot matrix printer is that it prints only in black and white.  The image printing ability is also very limited.  Daisy Wheel Printers  They can produce professional letter quality documents.  These printers are commonly referred to as letter quality printers as the print quality is as good as that of a high-quality typewriter.  They produce high-resolution output and are more reliable than dot matrix printers.  They can have speeds up to 90 cps.  These printers give only alphanumeric output. They cannot print graphics and cannot change fonts unless the print wheel is physically replaced.  They are slower and more expensive than dot matrix printers.  Drum Printers Page 16 ORGANIZATION OF COMPUTER SYSTEMS  Drum printers can print an entire line in a single operation. Hence, these printers are known as line printers.  Their printing speed varies from 150 lines to 2500 lines per minute with 96 to 160 characters on a 15-inch line.  Have limited multi-font capability, and often produce lower print quality than most recent printing technologies.  Line printers are designed for heavy printing applications. They are very expensive. 2. Non-impact Printers Non-impact printers are faster and quieter than impact printers, and you find them almost everywhere these days. Non-impact printers form characters and images without direct physical contact between the printing mechanism and the paper. Two types of non-impact printers often used with microcomputers are:  Laser printers  A laser printer creates images with dots. However, these images are created on a drum treated with magnetically charged ink-like toner (powder), and then transferred from drum to paper.  Laser printers produce resolutions at near-typeset quality;  Color printing is available in more expensive models.  Laser printers also have built-in RAM chips to store documents;  Built-in ROM chips to store fonts and other formatting; and their own small, dedicated processor.  Provide high speed and capabilities  A toner, a black granular dust, is used in the process  Prints up to 17 page per minute.  Ink Jet Printers Page 17 ORGANIZATION OF COMPUTER SYSTEMS Basically, considering color, monitors are grouped into two: monochrome display and color display. Monochrome displays actually display two colors: one for background, and one for foreground. These monitors show information using a single foreground color on a contrasting background color. For example, white on black, green on black or vise-versa The color monitor display many different colors. Many monitor display color combining shades of red, green, and blue (RGB). These RGB displays or monitors can create 256 colors and other several variations on them by blending shades of red, green and blue (hence they are called “RGB” Displays).  Resolution On the computer screen, all characters and images are produced as the result of combining dot patterns, which are also, called pixels. The number of these dots or pixel per one-inch space (abbreviated as DPL) on the screen determines the quality or sharpness (resolution) of the character or the image. That means, the higher the number of pixels on one-inch space, the quality of the image will be. Common or standard resolutions are:  640 columns X 480 rows of dots (307,200 pixels on the full screen)  800 columns X 600 rows (480,000 pixels)  1,024 columns X 768 rows (786,432 pixels)  Refresh Rate  Refresh rate is the number of times per second the pixels are recharged so that their glow remains bright.  Graphics Standard  It is related to resolution; graphics standards combine resolution and use of color. Page 20 ORGANIZATION OF COMPUTER SYSTEMS  A computer monitor is used with a graphics adapter card, an interface board between computer and monitor that performs one of severally used IBM compatible standards: color graphics adapter (CGA, the oldest and lowest resolution standard); enhanced graphics adapter (EGA), Video graphics array (VGA), and super VGA (SVGA which has the best resolution of all). There are different standards for monitors, and they support different color depths.  VGA (Video Graphic Array) VGA, for video graphics array, will support 16 to 256 colors depending on the resolution. At 320 x 200 pixels it will support 256 colors; at the sharper resolution of 640 x 480 pixels it will support 16 colors, which is called 4-bit color.  SVGA (Super Video Graphic Array) SVGA, for super video graphics array, will support 256 colors at higher resolution than VGA. SVGA has two graphics modes: 800 x 600 pixels and 1024 x 768. SVGA is called 8-bit color. Most new computers offer SVGA.  XGA (Extended Video Graphic Array) Also referred to as high-resolution display, XGA, for extended graphics array, supports up to 16.7 million colors at a resolution of 1024 x 768 pixels. Depending on the video display adapter memory chip, XGA will support 256, 65,536, or 16, 777,216 colors. At its highest quality, XGA is called 24-bit color, or true color. Note: Hard Disk Drive and Floppy Disk Drive are a special type of input and output devices. Page 21 ORGANIZATION OF COMPUTER SYSTEMS 3.2.4. The bus system Interconnecting Components in a Computer and Information Movement in a Computer System. We have seen that there are different components of a computer and each performs a specific function. But to perform a given task in synchronized form there should be some mechanism of communication. For this reason there is an electronic circuit which produces communication path between the different components of a computer system along which data are transferred, that is Bus. The bus, which communicates the different parts of the CPU, is called Internal Bus. And the bus, which communicates the CPU with memory and peripheral devices, is called External Bus. The size of the bus determines the speed of efficiency of the computer. Address Bus: - is a unidirectional bus over which digital information is transferred to identify either a particular memory location or particular I/O address. Data Bus: - a bus system which interconnects the CPU, memory and all the peripheral Input / Output devices of a computer system for the purpose of exchanging data. Control Bus: - a bus used to select and enable an area of main storage and transmit signals required to regulate the computer operation. It carries control signals that allow the CPU to control the transfer of information along the bus. For example, the CPU must be able to indicate whether information is to be transferred from memory or to memory; it must be able to signal when to start the transfer and so on. It is important to realize that a computer system may have a number of separate bus systems so that information can be transferred between more than one pair of components at the same time. For example, it is common to Page 22 ORGANIZATION OF COMPUTER SYSTEMS 3.3. Computer Software The computer hardware is an electronic device which has the potential of performing the task of solving a problem. However one has to give precise instructions to the hardware in order to solve problem. The finite set of instructions (steps) that the computer follow to perform a given job is called a program. Any program to be executed first it should reside / loaded/ in the memory. Software:- is a collection of programs and routines that support the operations of performing a task using a computer. Software also includes documentations, rules and operational procedures. Software makes the interface between the user and the electronic components of the computer. USER Software Hardware Computer software is classified into two 1. System software 2. Application software 3.3.1. System Software  Constitutes those programs which facilitate the work of the computer hardware.  It organizes and manages the machine’s resources, handles the input/output devices.  It controls the hardware by performing functions that users shouldn’t have to or are unable to handle.  System programs make complex hardware more user friendly. Page 25 ORGANIZATION OF COMPUTER SYSTEMS  It acts as intermediate between the user and the hardware.  It enables the computer understand programming languages i.e. it serves as means of communication between user and a computer. The important categories of system software are: A. Operating system B. Language software A. Operating system Operating system coordinates the activity between the user and the computer. An operating system has three major functions. i. Controlling operations (control program)  Coordinates, or supervises the activity of the computer system.  Decides where programs and data should be stored in the computer memory.  Handles communications among the computer components, applications software and the user.  Controls the saving and retrieving of files to and from disks in the disk drive.  It performs all its controlling tasks without the involvement or awareness of the user. ii. Input/output Management  The I/O manager coordinates the computers communication with outside world, flow of data to the display screen and other output devices (printers/ plotters) and from the key board or other input devices.  Handles the flow of data to and from the disk drives (file management).  Handles the process of preparing a disk for use, the copying, renaming, erasing task of a file. iii. Command Processing ( command Interpreter)  It interprets the commands or what you enter using the keyboard or other input devices.  If you write an internal command it carries out the function of that Page 26 ORGANIZATION OF COMPUTER SYSTEMS command if it is external command or other executable file it searches for the corresponding file in the default (current disk) or the user specified disk, loads the file into memory and transfers control to that program. Once this program is terminated, control returns to command and the program for that command or file is discarded from memory.  Types of Operating Systems Operating systems can be classified by: The number of programs they can handle at a time and The number of users they serve at once at one or different stations (i.e. terminals or micro-computers connected to a central computer). i. Single tasking operating systems  With single tasking operating systems: only one program can be run on a computer at a time.  In order to run another program, one must remove the first program loaded in the computers main memory and load the other one(i.e. it can’t handle two or more programs at a time)  These types of operating systems are single user or can serve only one user at a time. ii. Multi user operating system  It supports a number of work stations connected to a central system.  A number of users can use the resources of one high capacity computer by the help of terminals. iii. Real Time Operating System  A real time is a system that is capable of processing data so quickly that the results are available to influence the activity currently taking place.  Its primary characteristics is that it responds to an event within a well defined time. Page 27 ORGANIZATION OF COMPUTER SYSTEMS  Fewer errors are made and those made are easier to find. These programs are easier to modify.  Easier to learn  Easier to locate correct errors Disadvantage  Coding is time consuming. It is also machine-oriented program. The programmers must know the machine characteristics and requirements  The program size is big like machine codes  It is usually unique to a particular computer series  It is not directly executable by the computer. It needs assembler to translate it into machine codes  High Level Programming Language The high level programming languages are problem oriented unlike the machine language, which is machine oriented programming language. The high level languages are symbolic languages that use English like words and/or mathematical symbols rather than mnemonic codes. A programmer may not be needed to know the details of the internal logical structure of a computer. Some of the Common High Level Languages: FORTRAN, COBOL, PASCAL, C, C++, Java, etc. Advantage  Easier to learn and write the codes  Codes are written with out any particular machine in mind  Portable  Small program size  These languages may be used with different makes of computers with little modifications.  They are easier to learn.  They require less time to write. Disadvantage Page 30 ORGANIZATION OF COMPUTER SYSTEMS  Require more time to run and more computer memory space  Cannot access all components of the computer hardware such computer accessories. In that case we have to use lower level languages  They require additional time during translation  They are less efficient compared to the machine code languages. 3.3.2. Application Software  Is software that is designed to perform tasks for the specific area or areas. But for use in more than one installation.  Are usually called application packages as they may include a number of programs along with operating instruction, documentation and so forth.  Depending on their function or task they are categorized in to the following. 1. Word Processors/ Word processing - is a computerized typewriter which permits the electronic creation, editing, formatting, filing and printing text. - Is the most common application of microcomputers. - Until recently, word processing could be done only dedicated word processors. A dedicated word processor is a computer that denies its users the opportunity to execute any other program. Example: WordStar, WordPerfect, Microsoft word 2. Spreadsheet - is an electronic worksheet display on the VDU. - Until recently, financial analysis and other mathematical calculation were done by entering numbers on pages of an accountants ruled ledger pad. - You can quickly create a model of a situation on a spreadsheet by entering labels, numbers & formulas. - Using the programs built-in function you can perform complicated calculations such as net percent value, internal rates of return, and monthly payments on a loan. Example: Lotus 1-2-3, Microsoft Excel, Quatropro Page 31 ORGANIZATION OF COMPUTER SYSTEMS 3. Database management system. - Allow you to store information on a computer, retrieve it when you need it and update it when necessary. - You can do this with index cards, but database management programs do them more quickly and easily. - Example: You can store large mailing list, inventory record or billing and collect information in lists stored in files and manipulate this information, one file at a time with database management program. - You can record or create a database about employee information as Name, sex,Marital status, salary, Date of Birth, Date of employment, Post, Department, Level of education, Field of study, etc. Then you can ask the computer the following question - How many female workers are there? - List employees with a salary of birr 500 and above - List those employees who are department head and have Bachelor degree or higher and so on. Example: Dbase IV, FoxPro, Microsoft Access. Page 32