introduction to computers

introduction to computers

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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 92 5.1 BASIC COMPONENTS OF A COMPUTER The following five units (also called "The functional units") correspond to the five basic operations performed by all computer systems. Fig 5.1 Basic components of a computer Input Unit An input unit performs the following functions. 1. It accepts (or reads) the list of instructions and data from the outside world. 2. It converts these instructions and data in computer acceptable format. 3. It supplies the converted instructions and data to the computer system for further processing. Output Unit The following functions are performed by an output unit. 1. It accepts the results produced by the computer which are in coded form and hence cannot be easily understood by us. 2. It converts these coded results to human acceptable (readable) form. 3. It supplied the converted results to the outside world. Storage Unit The Storage Unit or the primary / main storage of a computer system provides space for storing data and instructions, space for intermediate results and also space for the final results. The specific functions of the storage unit are to store: 1. All the data to be processed and the instruction required for processing (received from input devices). 2. Intermediate results of processing. 3. Final results of processing before these results are released to an output device. Computer’s memory can be classified into two types; primary memory and secondary memory. a. Primary Memory can be further classified as RAM and ROM.
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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 93 • RAM or Random Access Memory is the unit in a computer system. It is the place in a computer where the operating system, application programs and the data in current use are kept temporarily so that they can be accessed by the computer’s processor. It is said to be ‘volatile’ since its contents are accessible only as long as the computer is on. The contents of RAM are no more available once the computer is turned off. • ROM or Read Only Memory is a special type of memory which can only be read and contents of which are not lost even when the computer is switched off. It typically contains manufacturer’s instructions. Among other things, ROM also stores an initial program called the ‘bootstrap loader’ whose function is to start the operation of computer system once the power is turned on. Fig 5.2 types of computer storage b. Secondary Memory These include devices that are peripheral and are connected and controlled by the computer to enable permanent storage of programs and data. Examples are CD ROM, Hard Disk and Digital Video Disk Central Processing Unit (CPU) The main unit inside the computer is the CPU. This unit is responsible for all events inside the computer. It controls all internal and external devices, performs "Arithmetic and Logical operations". The control Unit and the Arithmetic and Logic unit of a computer system are jointly known as the Central Processing Unit (CPU). The CPU is the brain of any computer system. Arithmetic and Logic Unit (ALU) The arithmetic and logic unit (ALU) of a computer system is the place where the actual execution of the instructions take place during the processing operations. All calculations are performed and all comparisons (decisions) are made in the ALU.
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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 94 Control Unit The control unit directs and controls the activities of the internal and external devices. It interprets the instructions fetched into the computer, determines what data, if any, are needed, where it is stored, where to store the results of the operation, and sends the control signals to the devices involved in the execution of the instructions. 5.2 I/O DEVICES Input/output devices are required for users to communicate with the computer. In simple terms, input devices bring information INTO the computer and output devices bring information OUT of a computer system. Examples of Input Devices are Keyboard, Mouse, Joystick, Scanner, Light Pen, Touch Screen etc 5.3 PRINTERS Printers are used to produce paper (commonly known as hardcopy) output. Based on the technology used, they can be classified as Impact or Non-impact printers. • Impact printers use the typewriting printing mechanism wherein a hammer strikes the paper through a ribbon in order to produce output. Dot-matrix and Character printers fall under this category. • Non-impact printers do not touch the paper while printing. They use chemical, heat or electrical signals to etch the symbols on paper. Inkjet, Deskjet, Laser, Thermal printers fall under this category of printers. When we talk about printers we refer to two basic qualities associated with printers: resolution, and speed. Print resolution is measured in terms of number of dots per inch (dpi). Print speed is measured in terms of number of characters printed in a unit of time and is represented as characters-per-second (cps), lines-per- minute (lpm), or pages-per-minute (ppm). 5.4 DISPLAY DEVICES A display device is an output device for presentation of information for visual or tactile reception, acquired, stored, or transmitted in various forms. When the input information is supplied as an electrical signal, the display is called electronic display. CRT MONITOR [cathode-ray tube] A CRT monitor contains millions of tiny red, green, and blue phosphor dots that glow when struck by an electron beam that travels across the screen to create a visible image. In a CRT monitor tube, the cathode is a heated filament. The heated filament is in a vacuum created inside a glass tube. The electrons are negative and the screen gives a positive charge so the screen glows. LCD Monitor
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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 95 Flat panel displays encompass a growing number of technologies enabling video displays that are lighter and much thinner than traditional television and video displays that use cathode ray tubes, and are usually less than 4 inches (100 mm) thick. They can be divided into two general categories: Volatile or Static Volatile Volatile displays require pixels be periodically refreshed to retain their state, even for a static image. This refresh typically occurs many times a second. If this is not done, the pixels will gradually lose their coherent state, and the image will "fade" from the screen. Examples of volatile flat panel displays  Plasma displays  Liquid crystal displays (LCDs)  Organic light-emitting diode displays (OLEDs)  Light-emitting diode display (LED)  Electroluminescent displays (ELDs)  Surface-conduction electron-emitter displays (SEDs)  Field emission displays (FEDs)  Nano-emissive display (NEDs) Static Static flat panel displays rely on materials whose color states are bitable. This means that the image they hold requires no energy to maintain, but instead requires energy to change. This results in a much more energy-efficient display, but with a tendency towards slow refresh rates which are undesirable in an interactive display. Examples of static flat panel displays  electrophoretic displays (e.g. E Ink's electrophoretic imaging film)  bichromal ball displays (e.g. Xerox's Gyricon)  Interferometric modulator displays (e.g. Qualcomm's iMod, a MEMS display.)  Cholesteric displays (e.g. MagInk, Kent Displays)  Bistable nematic liquid crystal displays (e.g. ZBD) 5.5 SCANNERS Scanner is an input device used for direct data entry from the source document into the computer system. It converts the document image into digital form so that it can be fed into the computer. Capturing information like this reduces the possibility of errors typically experienced during large data entry. The most common types are flatbed scanners, sheetfed scanners, photo scanners, and portable scanners. 5.6 MOTHER BOARD
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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 96 This is the main circuit board of the PC. It contains all the basic, core components of the computer. It usually contains:  The CPU, which plugs into a socket designed for a particular CPU's pin arrangement. Because a motherboard has sockets that can only accept certain types of CPU, it is important to make sure when upgrading your CPU that your motherboard can accept it.  Memory chips - these hold data and programs that the CPU is currently using.  Input/output ports ("I/O") such as connectors that hard disk drives, floppy disk drives and CD-ROM drives plug in to, serial port sockets, parallel port sockets and USB port sockets.  BIOS chips (Basic Input Output System) - the BIOS chips are PROM (Programmable Read Only Memory) chips that contain the most basic information that a computer needs to start up and operate. The BIOS contains bootup information, details of what sort of CPU is installed, what hard disks are available, how the motherboard should behave etc. Fig 5.3 Motherboard components  Real time Clock (RTC) so the computer knows the time and date. The RTC needs a battery to keep the clock running when the computer's power is turned off.
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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 97  Slots for the system's main memory, typically in the form of DRAM chips, Slots for one or more hard drives to store files. The most common types of connections are Integrated Drive Electronics (IDE) and Serial Advanced Technology Attachment (SATA). A slot for a video or graphics card  Chipsets is a group of small circuits that coordinate the flow of data to and from key components of a PC. This includes the CPU itself, the main memory, the secondary cache and any devices situated on the buses. The chipset also controls data flow to and from hard disks, and other devices connected to the IDE channels. A computer has got two main chipsets:- NorthBridge (also called the memory controller) is in charge of controlling transfers between the processor and the RAM, which is why it is located physically near the processor. SouthBridge (also called the input/output controller or expansion controller) handles communications between slower peripheral devices. • BUS: A bus is simply a circuit that connects one part of the motherboard to another. The more data a bus can handle at one time, the faster it allows information to travel. The speed of the bus, measured in megahertz (MHz), refers to how much data can move across the bus simultaneously Fig 5.3 buses in motherboard
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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 98 BIOS Basic input/output system, the built-in software that determines what a computer can do without accessing programs from a disk. On personal computers (PCs), the BIOS contains all the code required to control the keyboard, display screen, disk drives, serial communications, and a number of miscellaneous functions. The four main functions of a PC BIOS  POST - Test the computer hardware and make sure no errors exist before loading the operating system. Additional information on the POST can be found on our POST and Beep Codes page.  Bootstrap Loader - Locate the operating system. If a capable operating system is located, the BIOS will pass control to it.  BIOS drivers - Low level drivers that give the computer basic operational control over your computer's hardware.  BIOS or CMOS Setup - Configuration program that allows you to configure hardware settings including system settings such as computer passwords, time, and date. 5.7 SECONDARY STORAGE DEVICES Secondary storage device is any volatile medium that holds data until it is deleted or overwritten. Secondary storage is about two orders of magnitude cheaper than primary storage. Consequently, hard drives (a prime example of secondary storage) are the go-to solution for nearly all data kept on today's computers. There are several types of secondary storage media used today in the world, each of these can be compared to each other in terms of portability, speed and capacity. Currently the most common forms of secondary storage device are:  Floppy disks  Hard disks  Optical Disks  Magnetic Tapes.  Solid State Devices 5.7.1 Hard Disk HD Is a data storage device used for storing and retrieving digital information. The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000: a 1-terabyte (TB) drive has a capacity of 1,000 gigabytes.
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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 99 Five Main Components Platters - The aluminum alloy disks upon which data is stored. It's a magnetic media, somewhat akin to the surface preparation on a cassette tape. However, the surface of the platter is magnetically formatted (on both sides) into sectors and tracks where digital information is written. Spindle - the platters or disks spin on the spindle, which is run by a motor on the drive. I guess you could say it's kind of like the axle on a wheel. Read/Write Heads - The heads move across the platters to write data to, and read data from the platters. There's a read/write head for each side of each platter. Access is random, meaning that the heads can jump straight to the information they want without having to fast-forward or rewind past unneeded information. Head Actuator - Controls the read/write heads. The heads are at the end of an actuator arm which is attached to the actuator. Circuit board - Receives commands from the hard drive controller and translates them in order to move the head actuator, which moves the read/write head across the platters to the required position. Fig 5.4 Hard Disk Internal Structure Data is recorded onto the magnetic surface of a platter in exactly the same way as it is on floppies or digital tapes. Essentially, the surface is treated as an array of dot positions, with each domain’ of magnetic polarization being set to a binary 1 or 0. The position of each array element is not identifiable in an absolute sense, and so a scheme of guidance marks helps the read/write head find positions on the disk. The need for these guidance markings explains why disks must be formatted before they can be used. When it comes to accessing data already stored, the disk spins round very fast so that any part of its circumference can be quickly identified. The drive translates a read request from the computer into reality.
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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 100 There was a time when the cylinder/head/sector location that the computer worked out really was the data’s location, but today’s drives are more complicated than the BIOS can handle, and they translate BIOS requests by using their own mapping. Reading Data When the computer wants to read data, the operating system works out where the data is on the disk. To do this it first reads the FAT (File Allocation Table) at the beginning of the partition. This tells the operating system in which sector on which track to find the data. With this information, the head can then read the requested data. The disk controller controls the drive’s servo-motors and translates the fluctuating voltages from the head into digital data for the CPU. More often than not, the next set of data to be read is sequentially located on the disk. For this reason, hard drives contain between 256KB and 8MB of cache buffer in which to store all the information in a sector or cylinder in case it’s needed. This is very effective in speeding up both throughput and access times. A hard drive also requires servo information, which provides a continuous update on the location of the heads. This can be stored on a separate platter, or it can be intermingled with the actual data on all the platters. A separate servo platter is more expensive, but it speeds up access times, since the data heads won’t need to waste any time sending servo information. 5.7.2 Compact Disc A CD is 1.2 mm thick and rotates at a speed that varies between around 500 r.p.m. at the inside of the disc to around 200 r.p.m. at the outside (the disc is read from the inside to the outside). The speed reduces as the laser moves towards the outside of the disc to keep the linear read-out speed constant. This is usually 1.2 m/s, corresponding to a theoretical maximum playing time of 74 minutes. The frequency response of a CD is flat within ±0.5 dB from 5 Hz to 20 kHz, with a signal-to-noise ratio of better than 90 db. A compact disc (CD) is a flat, round, portable metal storage medium that usually is 4.75 inches in diameter and less than one-twentieth of an inch thick. Compact discs store items using microscopic pits (indentations) and land (flat areas) that are in the middle layer of the disc. A high-powered laser light creates the pits in a single track, divided into evenly spaced sectors, that spirals from the center to the edge of the disc. A low-powered laser reads items by reflecting light off the disc surface. The reflected light is converted into a series of bits that the computer can process.
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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 101 Fig 5.5 CD structure Some variations of the CD include: CD-Audio (CD-A) This kind of disc, commonly known as an audio CD, contains digitized recordings lasting up to 63, 74 or 80 minutes, depending on the length of the spiral on the disc, although the older 63 minute variety is now very rare. Audio CDs can be played on almost any kind of computer CD-ROM drive, as well as on a standard audio CD player. CD single he 8 cm ‘CD single’ was launched to take over the ‘singles’ function, with a maximum playing time of around 20 minutes and the same sound quality as a normal 12 cm CD. CD Graphics CD Graphics makes it possible to store song lyrics and other information on a CD, which can be displayed on a TV screen when a disc is played. CD-ROM Has a diameter of 12 cm and a storage capacity of 650 to 700 MB. A CD-ROM allows fast data access and has a very high reliability. This is why it is now universally used to store computer software and data. CD Video Three discs sizes - 12, 20 and 30 cm - were developed. The 12 cm 'CD with video' was referred to as 'CDV'. It contained up to 5 minutes of (analogue) video (like LaserDisc) plus up to 20 minutes of CD
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  MODULE 5 MCA-102DIGITAL SYSTEMS & LOGIC DESIGN ADMN 2014-‘17 Dept. of Computer Science And Applications, SJCET, Palai Page 102 digital audio, which could be played on any CD player. The 12 cm discs were yellow; to distinguish them from the silver audio CDs. Philips intended these discs to be an ideal carrier for video clips. 20 and 30 cm CD Video discs were also introduced, with playing times of 40 to 120 minutes. CD-i, the interactive CD The CD-i combined CD sound with video, text, animation and interactivity. This means that users could ‘communicate’ with a CD-i player and the software on the discs. CD-i disc had a capacity of 650 MB, allowing the storage of around 7,000 photos, 72 minutes of animation or 19 hours of speech. Or any combination of these, as the CD-i titles showed. Picture quality was also excellent, thanks to digital video with more than 16 million colors. Video CD A Video CD disc, with the same size as an audio CD, had a capacity of up to 74 minutes of digital audio and video. This meant that 2 discs were needed for a full-length movie, although these could be packaged in a box just as flat as a normal CD case, and much smaller than the same film on a video cassette or Laser Disc. CD-RW CD-Rewritable discs were initially much more expensive, is an erasable disc you can write on multiple times. 5.7.3 DVD A DVD-ROM (digital video disc-ROM) is an extremely high-capacity compact disc capable of storing from 4.7 GB to 17 GB. In order to read a DVD-ROM, you must have a DVD-ROM drive. You also can obtain recordable and rewritable versions of DVD. A DVD-R (DVD-recordable) allows you to write on it once and read (play) it many times. With the new rewritable DVD, called a DVD+RW, you can erase and record on the disc multiple times.