A computer is an electronic device, operating under the control of instructions stored in its own memory unit, that can accept data (input), process data arithmetically and logically, produce results (output), and store the results for future use.
Components of a computer
Strengths of Computers
Types of Computer
Increasing speed & processing power!
off or on digital value, short term for binary digits.
a group of eight bits, a unique code can be assigned to 256 different data possibilities. (e.g. 01000001 represents the letter A.)
ASCII (American Standard Code for Information Interchange)
It coordinates the flow of data and instructions. It contains a clock that generates a uniform stream of electrical pulses that synchronize the operating of the CPU and other computer components
Note: The control unit controls the computer by repeating 4 operations, called the machine cycle. The 4 operations are: fetching program instructions from memory; decoding the instructions into commands that the computer can process; executing the commands; and storing the results in memory Control Unit ALU Registers Memory Bus CPU
The Central Processing Unit
Arithmetic and Logic Unit (ALU)
It performs calculations and comparisons of data.
Control Unit ALU Registers Memory Bus CPU
They hold program instructions, data values, and memory locations as the computer executes a program.
The Central Processing Unit Control Unit ALU Registers Memory Bus CPU
They are electrical pathways that carry signal (bits) between a CPU’s components and outside devices.
The Central Processing Unit Control Unit ALU Registers Memory Bus CPU
Large computer systems, as well as newer workstations and network servers, frequently contain more than one central processing unit.
Multiple CPUs enable the computer to execute more than one instruction or process more than one program, at the same time.
Before programs are executed or data processed, they must first enter into main memory .
Main memory holds information read from disk or captured by input devices.
The CPU then moves information from the main memory into its registers for processing.
RAM ROM CACHE
Random Access Memory (RAM)
Integrated circuit containing data that can be read and written by the microprocessor or other devices.
Volatile - programs & data stored in RAM are erased when the power is off.
Chips that store information or instructions that can be read and used, but cannot be changed.
Non-volatile - retains its contents even the power is turned off.
The instructions to start the computer are on a special chip known as a ROM BIOS chip (Basic Input/Output System).
Read Only Memory (ROM)
Cache memory is a specialized chip used with the computer's memory.
Cache chips are faster and more expensive than regular RAM chips.
The computer stores the most frequently used instructions and data in cache. Cache has a relatively small storage capacity but can significantly increase the system's speed.
In summary, memory
accepts and holds program instruction and data
acts as the CPU’s source for data and instructions and as a destination for operation results
holds the final processed information until it can be sent to the desired output or storage devices, such as printer or disk drive
A circuit board that contains most of the electronic components of the system unit.
CPU Slot (PII) DIMM Sockets for Memory BIOS Chip Ports & Connectors Expansion Slots (for display card, modem card…)
Internet References How microprocessor works ( http://www.intel.com/education/mpuworks/index.htm ) Introduction to PC ( http://www.pcguide.com/intro/index.htm ) Computer Hardware ( http://www.ied.edu.hk/has/comp/component/index.htm ) Tom’s Hardware Guide ( http://www.tomshareware.com/guides/cpu.html ) Multimedia Tutorials (Available in SLCSS Intranet Only) Lab 1: Computer Fundamentals Lab 2: Central Processing Unit
2. Input Devices
Input devices, such as keyboards or scanners, are hardware components that capture, collect, and transmit data and programs to the computer in a form that computer can understand.
Input devices transmit the input to the computer in a series of electronic pulses representing bits, or digits, of the binary code.
Types of Input
raw facts that a computer receives and processes to produce information
instructions that direct the computer operations
key words that direct the computer to perform certain activities
data a user enters to respond to a question or message.
The most commonly used input devices.
Contains alphanumeric, cursors and function keys.
Function key Numeric keypad
Function Keys , labeled from F1 to F12, allow user to quickly access commands and functions, such as saving a document or calling up a program’s Help feature.
Cursor-control Keys govern the movement of the cursor on the screen. They include Up Arrow, Down Arrow, Left Arrow and Right Arrow key on the keyboard.
Special Purpose Keys are used in conjunction with other keys to enter commands into a computer. Control (Ctrl), Alternate (Alt) and Shift keys are example of special purpose keys.
Toggle Keys are keys that, when pressed, activates a certain mode or condition, and when pressed again, deactivates the condition. The Num Lock key, Cap Lock key and the Scroll Lock key are examples of toggle keys. (For example, pressing the Cap Lock key will cause all the alphanumeric characters to appear in capitals without holding down the Shift key.)
Numeric Keypad , located in the far right portion of the keyboard, is used for entering numbers quickly and for performing the same operations as a calculator.
Not all keyboards have the same layout. Most keyboards have adopted the so-called QWERTY layout for the alphanumeric keys.
Types of Keyboard 104-key keyboard Natural keyboard Keyboard for the Mac
B. Pointing Devices
Many people use pointing devices instead of keyboards whenever possible.
Pointing devices minimize the amount of typing (and the number of errors).
Palm-sized pointing devices
a ball on the bottom senses its movement
various actions can be preformed by moving the pointer and then pressing one of the buttons on top of the mouse.
Types of Mouse Cordless wheel mouse 3-button mouse Wheel mouse for notebooks iMouse for iMac
Mouse Interfaces Serial PS2 USB
Up-side down mouse
user rotates the ball itself while clicking nearby buttons
The mouse is not practical for people using a notebook computer in a small space. Track Point or Touch pad is therefore used instead to control the pointer.
Touch screens enable the user to select an option by pressing a specific part of the screen.
Touch screens are commonly used in grocery stores, fast-food restaurants, and information kiosks.
A touch screen kit solution
Use the movement of a vertical stem to direct the pointer.
C. Pen Input Devices
Input data with hand written characters, select items by pressing the pen against the screen, and use gestures, which are special symbols, to issue commands.
Used to select processing options or to draw on the screen
The tip of a light pen contains a highly sensitive photoelectric cell. When the light pen is pointed close to the screen, the photoelectric cell detects the light emitted from the exact spot the pen is touching. This accuracy makes light pens very popular among engineers and draftsmen who use computer-aided design (CAD) software to create blueprints and drawings of products or construction projects.
A digitizing tablet consists of a grid on which designs and drawings can be entered.
Most tablets are pressure-sensitive, and the user draws directly on the tablet using a special pen called a stylus.
Digitizing tablets are used to design cars, buildings, medical devices, and robots.
Chinese Handwriting Recognition Device
Used for inputting and recognizing Chinese handwriting
Nowadays, sophisticated Chinese handwriting recognition system also contains voice recognition function.
D. Scanning Devices
Electronically capture an entire image & convert it into digital form that can be processed by a computer
Image Scan Edit
Bar Code Reader
Bar code consists of a set of vertical lines and spaces of different widths
Universal Product Code (UPC) is very common
An example of a bar code
Magnetic Ink Character Recognition (MICR)
Use a special ink that can be magnetized during processing
MICR is used by the banking industry as a means of processing checks it receives in every day.
Magnetic Ink Character
Optical Character Recognition
OCR software can be installed in a computer to perform character recognition.
a system of producing machine-readable code on a data source item and reading that code by means of optical scanning devices.
Optical Mark Recognition
Optical marks are the filled-in shape, usually ovals or rectangles, on scan sheets.
The data collected on the scan sheets are translated into binary form by an optical mark reader (OMR)
Use lead pencil to mark on scan sheet Feed the scan sheets into the OMR
A smart card, often the size of a credit card, contains a built-in microprocessor and memory that identify the card (and its owner) and assists in financial and other transactions.
Its primary advantage is increased security: the information can only be read by an authorized user with appropriated password.
E. Multimedia Input Devices
Voice Input Devices
A voice input device has two functions:
First, it can simply record and play back the voice inputted by the user.
Secondly, it can record a human voice, then with appropriate voice recognition software , convert the voice input to ASCII characters.
Record images in a form that can be stored by a computer.
Some digital cameras resemble traditional cameras and are portable. Some are connected directly to a computer.
View Cam Digital camera
Video digitizers can capture input from virtually any type of video device, such as VCRs, televisions, and camcorders.
Audio digitizers can digitize music or voice from a microphone.
Internet References Jan’s Illustrated Computer Literacy 101 ( http://www.jegsworks.com/Lessons/lessonintro.htm ) Introduction to PC ( http://www.pcguide.com/intro/index.htm ) Computer Hardware ( http://www.ied.edu.hk/has/comp/compnent/index.htm ) Tom’s Hardware Guide ( http://www.tomshardware.com/guides/cpu.html ) Multimedia Tutorials (Available in SLCSS Intranet Only) Lab 3: Input/Output Devices
Also called secondary storage
store data & programs permanently for future use
can be used as both input & output devices
Magnetic Disk Storage
Most widely used storage medium
consists of a round piece of plastic or metal, the surface on which is covered by a magnetic materials.
e.g. floppy disks, hard disks and removable disk cartridge
Random-access storage medium
provides storage of 1.44MB data
A circular piece of thin plastic that is coated with magnetic material
the circular piece of plastic is enclosed by a rigid plastic shell
Formatting prepares a floppy disk for storage by defining the tracks, cylinders, and sectors on the disk surface
time required to locate data and transfer it to memory is called the access time .
Data is recorded on disk in concentric circular bands called tracks . The tracks on a disk are similar to the grooves on a phonograph record. Each track is divided into pie-shaped wedges called sectors . Two or more sectors combine to form a cluster .
Most computers maintain on the disk a table with the sector and track locations of data. This table, the file allocation table (FAT), enables the computer to locate data easily.
Structure of a Floppy Disk
Fixed in the System Unit
Consists of one or more rigid platters coated with a magnetic material
the platters, read/write heads, and the access arms that move the heads across the disk surface are all enclosed in an airtight, sealed case
Access time for a hard disk is significantly less than that for a floppy disk because a hard disk spins faster and unlike a floppy disk, a hard disk is spinning constantly (7200 revolutions per minute).
hard disks are permanently encased within the disk drive in a sealed environment free from dust and dirt. The disk can spin very rapidly, with the read/write head "floating" above the disk's surface.
Hard Disk Interfaces
To connect a hard disk to a microcomputer motherboard, you must have a hard disk interface.
This component includes circuitry that conforms to a standard recognized by both the hard disk and the motherboard manufacturer.
Common standards are Integrated Drive Electronics (IDE) and Small Computer System Interface (SCSI).
Provide both the storage capacity and fact access time of hard disk and the probability of floppy disks.
Iomega’s ZIP (100, 250, 750 MB)
Imation’s Superdisk (120MB)
Sony’s MO Disk (4~9GB)
Maintaining Stored Data
To prevent loss of data, 2 procedures should be performed regularly:
process of creating a copy of important programs and data
process of reorganizing data stored on a disk so that files are located in contiguous (adjacent) clusters.
CD-ROM and Optical Disks
By using laser technology, optical disk can store large quantities of data
a high power laser writes data on an optical disk by burning microscopic holes on the disk surface
a lower power laser reads the data by reflecting light off the disk surface. The reflected light is converted into a series of bits
CD-Read Only Memory
can store 650 MB data
suitable for reference material such as encyclopedias, catalogs and pictures
write once, read many
erasable; write many, read many
Floptical (Optical & Magnetic)
Consists of a thin ribbon of plastic, one side of which is coated with a material that can be magnetized to record binary data.
A sequential storage media (must write and read records on after another)
usually cartridge tape
serves as a primary means of
a method of transferring data between system, and
a cost-effective way to store data that does not have to be accessed immediately
Other types of Storage Devices
PC Cards (PCMCIA)
Compact Flash Memory Card
Types of Output
Output is data that has been processed into a useful form called information.
Types of Output
Most output can be divided into 2 categories: Soft copy & hard copy.
Soft copy is what you see on the monitor. Soft copy is temporary.
Hard copy can be touched and carried. Hard copy is usually some form of paper output.
A visual output device of a computer.
Monitor output is a most common form of soft copy.
CRT Monitor Flat-panel Monitor
Resolution of Display
Images on the screen are created by configurations of dots called pixels (picture elements)
The more the pixels, the better the resolution of the image
SVGA = pixel configuration of 800 by 600
XVGA = pixel configuration of 1024 by 768
Produce permanent output (hard copy)
consists of 2 main types: impact & non-impact
they can produce only text--no graphics.
Dot Matrix Printers
The most common character printers create images by using a dot pattern.
work in the same manner as copy machines; a laser beam creates electrical charges that attract toner to form an image and transfer it to paper.
Color Laser Printer Laser Printer
significantly less expensive than laser printers
relatively low resolution
Electronically charged ink is sprayed through a jet nozzle and passed through an electronic field, which deflects the ink to form a dot-matrix character
Other Output Devices
produce high-quality line drawings
A continuous-curve plotter is used to draw maps from stored data.
project a computer image onto screen
Voice Output Devices
generate spoken words from text
Computer Output microfilm (COM)
records output as microscopic images on roll film.