It ends at an interface called expansion slot on a motherboard.

PERIPHERALS Expansion Cards (ref.) It ends at an interface called expansion slot on a motherboard. With theses slots the system unit can be connected with other external peripheral devices by inserting different kinds of expansion cards (interface cards). Three main types of the slots: i. Accelerated Graphics Ports (AGP) : It holds a high-speed video graphics card for video applications. Peripheral Component Interconnect (PCI) slots : They are used for general-purpose expansion cards such as Network Interface Card (NIC) or sound card. i Industry Standard Architecture (ISA) slots : They are used for compatibility with earlier systems. Interfacing 介面 介面 (ref.) Peripheral devices are externally connected to a PC through different ports (or interfaces) Common types of ports: i. Serial ports. E.g. RS-232 interface or COM port. Parallel ports. E.g. printer port. i Universal Serial Bus (USB). It supports a maximum of 127 peripheral devices, transmitting data in serial mode at speed from 12Mbps up to 5Gbps (USB 3.0). iv. IEEE 1394 High Performance Serial Bus. It supports a maximum of 63 peripheral devices, transmitting data at speed up to 400Mbps. Input Device and Media (p.38 48) Input devices are responsible for the reading of information to be processed by the CPU. The input data are encoded onto an input medium; and an input device is used to convert the encoded data into a machine-sensible form, 0 or 1. **- same as machine-readable, is the name given to any data that is in a form suitable to be read into a machine such as a computer. Keyboard and keypads It has keys of alphabets and numbers arranged as those on. Other keys may include function keys, a calculator-like keypad, cursors keys, etc. It works with the VDU to form a terminal. Keying-in a character will result in a display of the character on the screen of the VDU. At the same time, the corresponding ASCII is sent to the CPU. PERIPHERALS page 1

In some computer connected peripheral devices such as Automatic Teller Machine (ATM), Stock Taking Devices, specially designed keypad are used where just a smaller number of keys and some function keys are present in them. Mouse, Trackball, Touchpad, Point Stick (trackpoint) Pointing Devices A mouse also works with the VDU. It controls the display of a VDU (mouse pointer) by its movement on a flat surface. It also has at least two bottom for single-click, double-click and right-click. On its bottom surface, there may be a moving ball or two lightemitting diode (LED) to sense its movement (optical mouse). Trackballs, touchpads and point sticks are similar in principle to a mouse except that you roll the ball or touch the pad instead of moving the body as in the mouse. (used in notebook computer) Game paddles / Joystick A game paddle is an analogue input device designed for playing computer games. An example is a joystick has a control stick controlling X-axis and Y- axis movement. Graphic Tablet It is a device that is used for manual graphic input. It consists of a grid of sensor wires and a cursor (or a pen). The cursor moves over the grid to specify the points on the graph. Touch Screen A menu is displayed on the screen. To choose an option, what you have to do is to use your finger to touch the option on the screen. The position of touching is recognized by photocells and infra-red light beams on the sides of the screen. Scanner It converts printed figures or pictures into computer sensible form by detecting the reflection of light from the built-in light source. Three types of scanners: flatbed scanner, paper-feeding scanner and hand-held scanners. As the flatbed scanners were the most reliable type giving image product of highest quality it is the most common type used nowadays. PERIPHERALS page 2

Digital camera / Digital Video Cameras / WebCam It functions like an ordinary camera except that the image is stored in digital format on the camera s internal memory and then storage media like specially designed memory cards. The larger the number of light-sensitive photosites in the light-sensitive processor chips, the higher the resolution of the digital image will be. A web cam is a special type of digital cameras connected to a computer. It may be used for video conferencing or remote surveillance. Document Reader (Source-data entry device) Sometimes, data are input to the CPU directly from source document by different types of document reader. Mark reader (Optical Mark Recognition, OMR) i. It senses the presence of marks in the prescribed position, by detecting the reflection of light or the conductivity (HB pencil mark). e.g. Multiple Choice answer sheet of HKCEE Optical Character Reader (Optical Character Recognition, OCR) i. It senses different characters by identifying their shapes photo-electrically. Advantages of OCR: a. The characters of OCR are humanly readable. b. Characters can be read by passing the scanner over them. The time and manual labour for data entry can be greatly reduced. i Limitation of OCR: a. The scanner must be properly placed over the characters along printed lines from left to right. b. OCR may not recognize all the characters without mistakes. Recognition for hand writing is still error Magnetic Ink Character Reader (Magnetic Ink Character Recognition, MICR) i. It senses different characters by recognition their shapes inscribed on documents with ink containing magnetized particles. It is usually found on bank cheques. Advantages of MICR: Figure 2 a. Magnetic ink characters are difficult to counterfeit. b. Like OCR, ordinary people can read these characters. c. Magnetic ink reader can read cheques with a high degree of accuracy and sort cheques at high speed. PERIPHERALS page 3

i Limitations of MICR: S6 ICT/CH/Sept 2013 a. There are only 10 digits, namely, 0 to 9, and 4 special characters, which are used exclusively by the banking industry. You cannot use alphabets or other symbols in MICR. b. The equipment used to print and read magnetic ink characters is very expensive and not widely available. It is limited to the bank cheques. c. To enable the reader to read the characters correctly, the magnetic ink character must be printed precisely at the right positions on the cheque. Handwriting Reader (Handwriting Recognition) When one writes on a pad, corresponding graphics appear on the screen. If it is an alphanumeric character, the reader can recognize it and the character is entered into the computer. It is usually used for input of Chinese characters as it is difficult to input Chinese characters using the traditional keyboard. Microphone It records sound into a computer. Microphones are usually connected to a sound card and the recorded sound can then be saved as a digitial file. Voice Recognition Recent research in voice recognition techniques enables data to be inputted into the computer verbally via microphone. The voice recognition system has to be trained to respond to the speech of a particular person, e.g. the person has to read 250 sentences into the system before the system can be used. It seems to be best method at all as it is the most natural for human beings to communicate with speech. However, the techniques still have some defects: i. Some words may be of the same phonetics. The computer has to recognize from the context of the speech. It is not suitable in quiet working environment. Point-Of-Sale Entry (POS) The point-of-sale may use punched tags, bar-codes or magnetic strips. It is used in shops where the input may invoke the calculation for the transaction and updating the transaction file. The input method must be fast to shorten the transaction time. Magnetic strip card reader It can read the magnetic strips on the back of bank cards and telephone cards. PERIPHERALS page 4

The magnetic strips store data appropriately for the application, e.g. the account number of the bank card or the amount of money remaining on the telephone card. Smart card reader (RFID, radio-frequency identification) A smart card contains a small processor and a small amount of memory storage. Smart cards are commonly used locally as a stored-value ticket for public transports like MTR, KCR and buses. Each time we take a train or bus journey, we place the card onto the reader. The reader then automatically updates the amount of money and records the fare and time of travel on the card. We can also increase the amount of money stored on the card by using a value adding machine at the station. Bar code reader A bar-code consists of varying thickness vertical lines that represent a unique code for the product. As a bar code reader is moved over the surface of the bar code, the data is recorded in the computer. In some supermarket, an optical wand is not necessary and the product can be put into an automatic laser scanning mechanism. Digitizer With a suitable interface it is now easy to plug in standard audio and video signal from a CD player, camcorder or a TV receiver, and digitise them into computer formats. The sound and graphic can usually be played or displayed in real time. As a result, it is now common to watch TV or listen radio on PC, or to monitor home through internet with small digital camera. Communication Device and Media (for both Input and Output) Modem It is used in transmitting data from one computer to another through telephone lines. It consists of a modulator and demodulator. Modulator data in computer Demodulator signal through telephone lines Network Interface Card (NIC) A network interface card (NIC) is a computer circuit board that is installed in a computer so that it can be connected to a network. Each NIC is unique. NICs provide a dedicated, full-time connection to a network. PERIPHERALS page 5

Output Device and Media Visual Display Unit (VDU) It is also known as monitor, as it helps to monitor the computer s operations. In addition to reflect the input key and mouse actions, the output data of process are also usually displayed by the VDU. All colours on the VDU are made up by a mixture of the three primary colours: RED, GREEN and BLUE ( RGB ). The Super VGA (SVGA) monitor that we use in our computer rooms has a resolution from 640 480, 1024 768 to 1600 1200 pixels, each can be one of 16 colours to 2 24 colours (i.e. 24 bit colours). The two common types of VDU are Cathode Ray Tube (CRT) display and Liquid Crystal Display (LCD). Another common type of display devices is the video projector. Printer It output data in paper forms (hardcopies). There are 3 types of printers: character printer : print 1 character at a time. line printer : print 1 whole line at a time. page printer : print 1 page at a time. Dot-matrix printer i. A character printer or line printer. Characters in a dot-matrix character impact printer are produced by printing appropriate dot patterns. Figure 3 PERIPHERALS page 6

i They are adequate for ordinary printout where print quality is not so important. S6 ICT/CH/Sept 2013 Ink-jet printer i. A line printer. It uses the dot-matrix principle droplets of electrically charged ink injected through a nozzle toward the paper instead of impact. Laser printer i. A page printer. Printing process: The laser printers use a laser beam to create images onto a drum. The images are electronically charged to attract toner, which is then transferred from the drum onto paper. A heating process follows which fixes the images onto the paper. i It produces the best quality printouts among the printers we study and thus is widely used for business printing. Thermal printer i. A thermal printer produces printed image by selectively heating thermal paper when the paper passes over the thermal print head. The coating of the thermal paper turns black in the areas where it is heated. Figure 4 Figure 5 PERIPHERALS page 7

Comparison between printers Dot-matrix Ink-jet Laser Cost Low Medium High Speed Slow Fast Very fast Quality Good Very good Excellent Popularity Low High for home use High for business use Plotter It is designed to draw continuous curves instead of discrete characters or matrix of dots, resulting in the form of graphics or pictures. It is commonly used in drawing professional diagram for building and cars or maps. Three kinds of plotters: flatbed, rotary (drum) and turtle. Figure 6 Video Projectors A video projector projects projects the computer display onto a large screen by using a high intensity light bulb and a set of optical lenses. The quality of a video projector is usually measured by the display resolution and the brightness (lumens). Other output media Microfilm and Microfiches, Voice synthesiser, Braille embosser PERIPHERALS page 8

Storage Devices (Backing Store, Secondary memory) The reasons for not putting data only in main memory: i. main memory is expensive; data in main memory is not permanent (i.e. volatile); i if all data are stored in main memory, the size of main memory will be very large and accessing time of data in it will thus be very long. Magnetic Tape Data in it is stored in vertical columns of frames. A magnetic tape drive is used to read and to write magnetic tape. It is done by a read/write head. After a block of data is written, it is read back immediately for checking. The storage density of a magnetic tape is expressed in terms of bits per inch (bpi). The maximum number of bytes that can be read from or written on tape in a second is called data transfer rate. (byte per second, bps, or character per second, cps) On a magnetic tape, we must read or write from beginning to the end - sequential access. Figure 8 PERIPHERALS page 9

Advantages of magnetic tapes: i. Compact Economical i Fast Transfer Rate Limitation of magnetic tapes: Allows only sequential access Magnetic Disks A magnetic disk is a circular sheet(s) of plastic material or metal (harddisk). Magnetic materials is coated on both surfaces. Data are stored as strings of bits along concentric circles, called track. The disk surface is also divided into pie-shaped segments, called sector. i Figure 9 The mapping of a symbolic filename on to a physical location in a disk is achieved by means of a file directory or catalogue on the disk (e.g. File Allocation Table, FAT) - a table containing information about the locations of named files. Each record of data on a disk is addressed by a track number and a sector number. hence allowing random access. We can still read or write a magnetic disk sequentially, depending on our needs. i.e. It supports both sequential and random access. Two main kinds of magnetic disks: Harddisks and floppy disks (floppies). Harddisk stores much more data than a floppy diskette. However, floppies are more portable and inexpensive. The lifetime of a floppy is much shorter than a harddisk. Advantages of magnetic disk over magnetic tape: i. Direct access Easy updating PERIPHERALS page 10

The common formats of floppy disks are shown below: Size Notation Sides Tracks Sectors Total 5.25 DSDD 2 40 8 320K 5.25 DSDD 2 40 9 360K 5.25 DSHD 2 80 15 1200K 3.5 DSDD 2 80 9 720K 3.5 DSHD 2 80 18 1440K CD - ROM ( Compact Disc Read-Only Memory ) It uses the same techniques and is same in size as the audio compact disc; therefore, is good for circulating information in large value, storing archival information that can be retrieved later by searching under certain criteria. Now it has increasing importance as its low price and large volume. The only limitation is that it is unwritable. Figure 10 As the technology makes progress compact disk recordable (CD-R) and compact disk rewritable (CD-RW) i. CD-R can be written once but can be read many times. CD-RW can be read and written many times. DVD ( Digital Video Disk or Digital Versatile Disk ) It is different in format with the CD-ROMs. DVD can store a greater amount of data than a traditional CD. A double-sided DVD can store 17 GB of data. The DVD has many different variations: DVD+R, DVD-R, DVD+RW, DVD-RW and DVD-RAM. High-definitino digital versatile disc (HD DVD) and Blu-ray Disc are high density optical disc formats designed for storing digital media, such as high definition video. Magneto-optical (MO) Disks The MO disk drive uses a combination of magnetic and optical methods to read and write data fromand to the MO disk. PERIPHERALS page 11

Flash memory Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed. It is a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory, a type of ROM, refer to p. 3). It is a technology that is primarily used in memory cards and USB flash drives for general storage. Memory cards. i. A memory card is a solid-state electronic flash memory data storage device used with digital cameras, handheld and Mobile computers, telephones, music players, video game consoles, and other electronics. From the late 1990s into the early 2000s a host of new formats appeared, including SD/MMC, Memory Stick, xd-picture Card, and a number of variants and smaller cards. USB flash drives i. A USB flash drive is a flash memory data storage device integrated with a USB (refer to p. 5) interface. USB flash drives are typically removable and rewritable, much shorter than a floppy disk and weigh less than 60 g. i Storage capacities typically range from 64 MB to 32 GB with steady improvements in size and price per gigabyte. iv. USB Memory card readers are also available, whereby rather than being built-in, the memory is a removable flash memory card housed in Comparison between backing store and main memory Main memory Backing store technology semi-conductor magnetic disk magnetic tape physical size small larger storage capacity small larger cost expensive cheap (cents per bit) (50-500) 0.05-0.0025 0.005-0.0005 access time very fast (10-3 - 10-2 µs) fast (3-30 ms) slow (10s - 10 min) permanence of data volatile for RAM non-volatile for ROM non-volatile read/write mode read/write read-only read/write access mode random and direct random and direct sequential function Stores programs and data which are begin processed stores backup copies or large volume interactive results PERIPHERALS page 12