Computer System Components

Computer System components

Computer system

Hardware Software Live ware

Computer system

Computer systemA computer system is the integration of physical entities called

hardware and non-physical entities called software. The hardware components include input devices, processor, storage devices output devices and Communication technologies. The software items are programs and operating aids(systems) so that the computer can process data.

Functional Units of a Computer SystemComputer system is a tool for solving problems. The hardware

should be designed to operate as fast as possible. The software(system software) should be designed to minimize the amount of idle computer time and yet provide flexibility by means of controlling theoperations. Basically any computer is supposed to carry out thefollowing functions.

Accept the data and program as input

Store the data and program and retrieve as and when required.

Process the data as per instructions given by the program and convert it into useful information

Communicate the information as output

Based on the functionalities of the computer, the hardwarecomponents can be classified into four main units, namely- Input Unit- Output Unit- Central Processing Unit-Memory Unit-Communication technologies

These units are interconnected by minute electrical wires topermit communication between them. This allows the computer tofunction as a system. The block diagram is shown below.

THE CENTRAL PROCESSING UNIT

The central processing unit (CPU) performs the actual computation or “number crunching” inside any computer. The CPU is a microprocessor (for example, a Pentium 4 by Intel) made up of millions of microscopic transistors embedded in a circuit on a silicon wafer or chip. (Hence, microprocessors are commonly referredto as chips.) Examples of specific microprocessors are listed in Table

the microprocessor has different parts, which perform different functions. The control unit sequentially accesses program instructions, decodes them, and controls the flow of data to and from the ALU, the registers, the caches, primary storage, secondary storage, and various output devices. The arithmetic-logic unit (ALU) performs the mathematic calculations and makes logical comparisons. The registers are high-speed storage areas that store very small amounts of data and instructions for short periods of time.

H o w t h e C P U W o r k s

The CPU, on a basic level, operates like a tiny factory. Inputs come in and are stored until needed, at which point they are retrieved and processed and the output is stored and then delivered somewhere. Figure illustrates this process, which works as follows:

• The inputs are data and brief instructions about what to do with the data. These instructions come from software in other parts of the computer. Data might be entered by the user through the keyboard, for example, or read from a data file in another part of the computer. The inputs are stored in registers until they are sent to the next step in the processing. • Data and instructions travel in the chip via electrical pathways called buses. The size of the bus—analogous to the width of a highway—determines how much information can flow at any time.• The control unit directs the flow of data and instructions within the chip.• The arithmetic-logic unit (ALU) receives the data and instructions from the registers and makes the desired computation. These data and instructions have been translated into binary form, that is, only 0s and 1s. The CPU can process only binary data.

• The data in their original form and the instructions are sent to storage registers and then are sent back to a storage place outside the chip, such as the computer’s hard drive Meanwhile, the transformed data go to another register and then on to other parts of the computer

This cycle of processing, known as a machine instruction cycle, occurs millions of times per second or more. It is faster or slower, depending on the following four factors of chip design:

I. clock speedThe preset speed of the clock that times all chip activities, measured in megahertz (MHz), millions of cycles per second, and gigahertz (GHz), billions of cycles per second. The faster the clock speed, the faster the chip. (For example, all other factorsbeing equal, a 1.0 GHz chip is twice as fast as a 500 MHz chip.)

I. word lengthThe word length, which is the number of bits (0s and 1s) that can be processed by the CPU at any one time. The majority of current chips handle 32-bit word lengths, and the Pentium 4 is designed to handle 64-bit word lengths. Therefore, the Pentium 4 chip will process 64 bits of data in one machine cycle. The larger the word length, the faster the chip.

II. bus widthThe bus width. The wider the bus (the physical paths down which the data and instructions travel as electrical impulses), the more data can be moved and the faster the processing. A processor’s bus bandwidth is the product of the width of its bus (measured in bits) times the frequency at which the bus transfers data (measured in megahertz). For example, Intel’s Pentium 4 processor uses a 64-bit bus that runsat 400 MHz. That gives it a peak bandwidth of 3.2 gigabits per second.

I. line widthThe physical design of the chip. Back to our “tiny factory” analogy, if the “factory” is very compact and efficiently laid out, then “materials” (data and instructions) do not have far to travel while being stored or processed. We also want to pack as many “machines” (transistors) into the factory as possible. The distance between transistors is known as line width. Historically, line width has been expressed in microns(millionths of a meter), but as technology has advanced, it has become more convenient to express line width in nanometers (billionths of a meter). Currently, most CPUs are designed with 180-nanometer technology (0.18 microns), but chip manufacturers are moving to 130-nanometer technology (0.13 microns). The smaller the line width, the more transistors can be packed onto a chip, and the faster the chip.

These four factors make it difficult to compare the speeds of different processors. As a result, Intel and other chip manufacturers have developed a number of benchmarks to compare processor speeds.

Functions of a Central Processing UnitThe CPU is the brain of the computer system. It performsarithmetic operations as well as controls the input, output and storage units. The functions of the CPU are mainly classified into two categories :- Co – ordinate all computer operations- Perform arithmetic and logical operations on dataThe CPU has three major components.- Arithmetic and Logic Unit- Control Unit-Registers (internal memory)

The arithmetic and logic unit (ALU) is the part of CPU whereactual computations take place. It consists of circuits which performarithmetic operations over data received from memory and arecapable of comparing two numbers.

The control unit directs and controls the activities of the computer system. It interprets the instructions fetched from the main memory of the computer, sends the control signals to the devices involved in the execution of the instructions.While performing these operations the ALU takes data fromthe temporary storage area inside the CPU named registers. Theyare high-speed memories which hold data for immediate processingand results of the processing.

Memory UnitMemory units are the storage areas in a computer. The term“memory” usually refers to the main memory of the computer,whereas, the word “storage” is used for the memory that exists ondisks, CDs, floppies or tapes. P r i m a r y S t o r a g eThe main memory is usually called aphysical memory which refers to the ‘chip’ (Integrated Circuit) capable of holding data and instruction.There are different types of memory. They are

I. Random Access Memory (RAM),II. Read Only Memory (ROM),III. Programmable Read-Only Memory (PROM),IV. Erasable Programmable Read-Only Memory(EPROM),V. Electrically Erasable Programmable Read-Only Memory

(EEPROM).

Random Access Memory - RAMRAM is the most common type of memory found in the moderncomputers. This is really the main store and is the place where theprogram gets stored. When the CPU runs a program, it fetches theprogram instructions from the RAM and carries them out. If the CPU needs to store the results of the calculations it can store them in RAM. When we switch off a computer, whatever is stored in theRAM gets erased. It is a volatile form of memory.

Read Only Memory - ROMIn ROM, the information is burnt (pre-recorded) into the ROMchip at manufacturing time. Once data has been written into a ROM chip, it cannot be erased but you can read it. When we switch off the computer, the contents of the ROM are not erased but remain stored permanently. ROM is a non-volatile memory. ROM stores critical programs such as the program that boots the computer.

Programmable Read Only Memory - PROMPROM is a memory on which data can be written only once. A variation of the PROM chip is that it is not burnt at the manufacturing time but can be programmed using PROM programmer or a PROM burner. PROM is also a non-volatile memory.Erasable Programmable Read Only Memory - EPROMIn EPROM, the information can be erased and reprogrammed using a special PROM – programmer. EPROM is non-volatile memory. A EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. But an ultraviolet light is used to erase the contents of the EPROM.Electrically Erasable Programmable Read Only Memory- EEPROMEEPROM is a recently developed type of memory. This is equivalent to EPROM, but does not require ultraviolet light to erase its content. It an be erased by exposing it to an electrical charge. It is also non-volatile in nature. EEPROM is not as fast as RAM or other types of ROM. A flash memory is a special type of EEPROM.

Cache memoryCache memory is a type of high-speed memory that a processor can access more rapidly than main memory (RAM).

M e m o r y C a p a c i t yAs already noted, CPUs process only 0s and 1s. All data are translated through computer languages (covered in the next chapter) into series of these binary digits, or bits. A particular combination of bits represents a certain alphanumeric character or simple mathematical operation. Eight bits are needed to represent any one of these characters. This 8-bit string is known as a byte. The storage capacity of a computer is measured in bytes. (Bits are used as units of measure typically only for telecommunications capacity, as in how many million bits per second can be sent through a particular medium.) The hierarchy of byte memory capacity is as follows:

• Kilobyte. Kilo means one thousand, so a kilobyte (KB) is approximately one thousandbytes. Actually, a kilobyte is 1,024 bytes (210 bytes).• Megabyte. Mega means one million, so a megabyte (MB) is approximately one millionbytes (1,048,576 bytes, or 1,024 1,024, to be exact). Most personal computers have hundreds of megabytes of RAM memory (a type of primary storage, discussed in a later section).• Gigabyte. Giga means one billion; a gigabyte (GB) is actually 1,073,741,824 bytes(1,024 1,024 1,024 bytes). The storage capacity of a hard drive (a type of secondary storage, discussed shortly) in modern personal computers is often many gigabytes.• Terabyte. One trillion bytes (actually, 1,078,036,791,296 bytes) is a terabyte.

S e c o n d a r y S t o r a g eSecondary storage is designed to store very large amounts of data for extended periods of time. Secondary storage can have memory capacity of several terabytes or more and only small portions of that data are placed in primary storage at any one time. Secondary storage has the following characteristics:It is nonvolatile.• It takes much more time to retrieve data from secondary storage than it does fromRAM because of the electromechanical nature of secondary storage devices.• It is much more cost effective than primary storage (see Figure 3.6).• It can take place on a variety of media, each with its own technology, as discussednext.

• The overall trends in secondary storage are toward more direct-access methods, higher capacity with lower costs, and increased portability.

Magnetic disks come in a variety of styles and are popular because they allowmuch more rapid access to the data than does magnetic tape. Magnetic disks, called hard disks or fixed disk drives, are the most commonly used mass storage devices because of their low cost, high speed, and large storage capacity. Fixed disk drives read from, and write to, stacks of rotating magnetic disk platters mounted in rigid enclosures and sealed against environmental or atmospheric contamination. These disks are permanently mounted in a unit that may be internal or external to the computer.

The read/write heads are attached to arms that hover over the disks, moving in and out (see Figure 3.8). They read the data when positioned over the correct track and when the correct sector spins by. Because the head floats just above the surface ofthe disk (less than 25 microns), any bit of dust or contamination can disrupt the device. When this happens, it is called a disk crash and usually results in catastrophic loss of data. For this reason, hard drives are hermetically sealed when manufactured.

Optical storage devices. Unlike magnetic media, optical storage devices do not store data via magnetism. As shown in Figure 3.9, to record information on these devices, a pinpoint laser beam is used to burn tiny holes into the surface of a reflective plastic platter (such as a compact disk). When the information is read, another laser, installed in the optical disk drive of the computer (such as a compact disk drive), shines on thesurface of the disk. If light is reflected, that corresponds to one binary state. If the light shines on one of the holes burned by the recording laser, there is no reflection and the other binary state is read. Compared to magnetic media, optical disk drives are slower than magnetic hard drives. On the other hand, they are much less susceptible to damage from contamination and are also less fragile.

Types of optical disks include compact disk read-only memory (CD-ROM), digital video disk (DVD), and fluorescent multilayer disk (FMD-ROM).

Memory cards. PC memory cards are credit-card-size devices that can be installed in an adapter or slot in many personal computers. The PC memory card functions as if it were a fixed hard disk drive. The cost per megabyte of storage is greater than for traditional hard disk storage, but the cards do have advantages. They are less failure prone than hard disks, are portable, and are relatively easy to use. Software manufacturers often store the instructions for their programs on a memory card for use with laptop computers. The Personal Computer Memory Card International Association (PCMCIA) is a group of computer manufacturers who are creating standards for these memory cards.

E n t e r p r i s e S t o r a g e S y s t e m sThe amount of digital information is doubling every two years. As a result, many companies are employing enterprise storage systems. An enterprise storage system is an independent, external system with intelligence that includes two or more storage devices. These systems are an alternative to allowing each host or server to manage its own storage devices directly. Enterprise storage systems provide large amounts of storage, high-performance data transfer, a high degree of availability, protection against data loss, and sophisticated management tools.There are three major types of enterprise storage subsystems: redundant arrays ofindependent disks (RAIDs), storage area networks (SANs), and network-attachedstorage (NAS).

Redundant array of independent disks. Hard drives in all computer systems are susceptibleto failures caused by temperature variations, head crashes, motor failure, controller failure, and changing voltage conditions. To improve reliability and protect the data in their enterprise storage systems, many computer systems use redundant arrays of independent disks (RAID) storage products. RAID links groups of standard hard drives to a specialized microcontroller. The microcontroller coordinates the drives so they appear as a single logical drive, but they take advantage of the multiple physical drives by storing data redundantly, thus protecting against data loss due to the failure of any single drive.

Storage area network. A storage area network (SAN) is an architecture for buildingspecial, dedicated networks that allow rapid and reliable access to storage devices bymultiple servers. Storage over IP, sometimes called IP over SCSI or iSCSI, is a technologythat uses the Internet Protocol to transport stored data between devices withina SAN. Storage visualization software is used with SANs to graphically plot an entirenetwork and allow storage administrators to view the properties of, and monitor, alldevices from a single console.Network-attached storage. A network-attached storage (NAS) device is a specialpurposeserver that provides file storage to users who access the device over a network. The NAS server is simple to install (i.e., plug-and-play), and works exactly like a general-purpose file server, so no user retraining or special software is needed.

1.5 INPUT DEVICESInput devices accept data and instructions from the user. Following are the examples of various input devices, which are connected to the computer for this purpose.1. Keyboard2. Mouse3. Light Pen4. Optical/magnetic Scanner5. Touch Screen6. Microphone for voice as input7. Track Ball

1.5.1 KeyboardA keyboard (as shown in figure 1.3) is the most common inputdevice. Several kinds of keyboards are available, but theyresemble each other withminor variations. Thekeyboard in most commonuse is the QWERTY board.Generally standardkeyboard has 104 keys. Inthese keyboards, the cursorcontrol keys are duplicatedto allow easier use of thenumeric pad.

1.5.2 MouseA mouse is an electro-mechanical, hand-held device (as shown in figure 1. 4). It is used as a pointer. It can perform functions like selecting menu commands, moving icons, resizing windows, starting programs, and choosing options.

The most common mouse uses an internal, magnetically coatedball, to detect the movement of the mouse across a flat surface,usually a desktop. Now a days Optical or laser mouse is used todetect the movement. All windows based applications today aredesigned to work with a mouse. A mouse is used to replace hard-to-remember key combinations with easier "Point and Click"actions. However, it cannot substitute all keyboard operations.It can be alternative for commands based operations.

1.5.3 Light penAn input device that utilizes a light-sensitive detector to select objects on a display screen. A light pen is similar to a mouse (as shown in figure 1.5), except that with a light pen you can move the pointer and select objects on the display screen by directly pointing to the objects with the pen.

1.5.4 Optical ScannerThese devices are used for automatic data collection. The devices of this category completely eliminate manual input of data. For example, the bar-code reader is actually just a special type of image scanner. An image scanner translates printed images into an electronic format that can be stored in a computer’s memory, and with the right kind of software, one can alter a stored image. Another example of scanner is optical character recognition (OCR) device, used by banks to convert the scanned image of a typed or printed page into text that can be edited on the computer.

1.5.5 Touch ScreenTouch panel displays and pads are now being offered as lternatives to keyboard. Here the input can be given through the computer screen, that accepts the input through monitor; users touch electronic buttons displayed on the screen or they may use light pen.

1.5.6 MicrophoneMicrophone is an input device, which takes voice as input. The voice communication is more error-prone than information through keyboard. There are two types of microphones available (as shown in figure 1.8):

1.5.7 Track BallTrackball, a pointing device, is a mouse lying on its back (as shown in figure 1. 9). To move the pointer, you rotate the ball with your thumb, your fingers, or the palm of your hand. There are usually oneto three buttons next to the ball, which you use just like mouse buttons. The advantage of trackballs over mouse is that the trackball is stationary so it does not require much space to use it. In addition,you can place a trackball on any type of surface, including your lap. For both these reasons, trackballs are popular pointing devices for portable computers.

1.6 OUTPUT DEVICESOutput devices return processed data that is information, backto the user. Some of the commonly used output devices are:

1. Monitor (Visual Display Unit)2. Printers3. Plotter4. Speakers

1.6.1 MonitorOut of all the output devices, monitor (as shown in figure 1.10) is perhaps the most important output device because people interact with this device most intensively than others. Computerinformation is displayed, visually with a video adapter card and monitor. Information processed within the CPU, that needs to be visually displayed, is sent to video adapter. The video adapter converts information from the format used, in the same manner as a television displays information sent to it by a cable service.

Two basic types of monitors are used with microcomputers, which are as follows:

Cathode Ray Tube (CRT): CRT or Cathode Ray Tube Monitor is the typical monitor that you see on a desktop computer. It looks a lot like a television screen, and works the same way. This type uses a large vacuum tube, called cathode ray tube (CRT). Liquid Crystal Displays (LCD): This type of monitors are also known as flat panel monitor. Most of these employ liquid crystal displays (LCDs) to render images. These days LCD monitor are very popular.When people talk about the capabilities of various monitors, onecritical statistic is the resolution of the monitor. Most monitors have a resolution of at least 800 x 600 pixels. High-end monitorscan have resolutions of 1024 x 768 pixels or even 1280 x 1024 pixels. Thus monitors are available either in low resolution or in high resolution.

1.6.2 PrinterAfter a document is created on the computer, it can be sent to aprinter for a hard copy (printout). Some printers offer specialfeatures such as colored and large page formats. Some of themost commonly used printers are:1. Laser Printer2. Ink Jet Printer3. Dot Matrix Printer4. Line PrinterLaser Printer: A laser printer produces high quality print that one normally finds in publishing. It is extremely fast and quiet. Moreover, the operation of a laser printer is easy with automatic paper loading and no smudging or messing up of ink ribbons. The fastest laser printer. can print up to 200 pages per minute in monochrome (black and white) and up to 100 pages per minute in color.

Ink-Jet Printer: An ink-jet printer creates an image directly on paper by spraying ink through as many as 64 tiny nozzles. Although the image it produces is not generally quite as sharp as the output of a laser printer, the quality of ink-jet images is still high. In general, ink-jet printer offers an excellent middle ground between dot matrix and laser printer. Like laser printer, an ink-jet printer is quiet and convenient, but not particularly fast. Typically, an ink-jet printer is more expensive than a dot-matrix printer, but costs only half as much as a laser printer.

Dot Matrix Printer: The dot matrix printer was very popular at one point of time. It is a very versatile and inexpensive output device. In dot matrix printer the print head physically "hits" the paper through the ribbon and produces text (or images) by combinations of dots; hencethe name dot matrix printer. Its speed is measured in characters per second (CPS). Although it is less expensive, it is louder, slower and produces lower print quality.

Line Printer: A line printer is generally used with large computer systems to produce text based data processing reports. Line printers are high-speed printers with speeds ranging anywhere from 100 to about 3800 lines per minute. In the past, print quality on line printerswas not high. Developments in technology are improving the print quality on line printers. These are in the cost range of lacs of Rupees.

1.6.3 PlotterA plotter is a special kind of output device that, like a printer,produces images on paper, but does so in a different way. Plottersare designed to produce large drawings or images, such as construction plans for buildings or blueprints for mechanicalobjects. A plotter can be connected to the port normally used bya printer.

An array of different colored pens in a clip rack and a robotic armis part of plotter. The instructions that a plotter receives from acomputer consist of a color, and beginning and ending

coordinates for a line. With that information, the plotter picks upthe appropriate pen through its arm, positions it at the beginning coordinates drops the pen down to the surface of the paper anddraws to the ending coordinates. Plotters draw curves by creating a sequence of very short straight lines.Plotters usually come in two designs:1. Flat Bed: Plotters of small size to be kept on table withrestriction of paper size.2. Drum: These plotters are of big size using rolls of paper ofunlimited length.Fig. 1.15 Flat bed and Drum Plotter

1.6.4 SpeakerSpeakers (as shown in figure 1.16) are another type of output device, which allow you to listen to voice like music, and conversation with people.