computer hardware

Computer, machine that performs tasks, such as calculations or electronic communication, under the control of a set of instructions called a program. Programs usually reside within the computer and are retrieved and processed by the computer’s electronics. The program results are stored or routed to output devices, such as video display monitors or printers. Computers perform a wide variety of activities reliably, accurately, and quickly.

It is an electronic machine that can accept, store, manipulate, and retrieve data and information.
PARTS OF A COMPUTER SYSTEM: hardware, software, and peopleware.

Computer hardware consists of the components that can be physically handled. The function of these components is typically divided into: CPU, input technologies, output technologies, memory, and communications technology.

CPU
CPUs contain processing units that interpret and implement software instructions, perform calculations and comparisons, make logical decisions (determining if a statement is true or false based on the rules of Boolean algebra), temporarily store information for use by another of the CPU’s processing units, keep track of the current step in the execution of the program, and allow the CPU to communicate with the rest of the computer.

A CPU is similar to a calculator, only much more powerful. The main function of the CPU is to perform arithmetic and logical operations on data taken from memory or on information entered through some device, such as a keyboard, scanner, or joystick. The CPU is controlled by a list of software instructions, called a computer program.

It consists of: Arithmetic/Logic Unit (ALU) - which performs calculations and comparisons. It performs specific operations such as addition, multiplication, and conditional tests.
Control Unit – which controls other hardware functions
Registers - store data and keep track of operations
Internal bus - connects the units of the CPU with each other and with external components of the system

INPUT TECHNOLOGIES
These are devices that permit the computer user to communicate with the computer.

HUMAN DATA ENTRY DEVICES Needs data entered by a user. These devices allow people to communicate with the computer.

Keyboard - keypad device with buttons or keys that a user presses to enter data characters and commands into a computer. Keyboards emerged from the combination of typewriter and computer-terminal technology.

Patterned from the typewriter’s QWERTY which was invented by American typewriter inventor and printer, Christopher Sholes in the 1890’s. The computer keyboard can be attached to the system unit through cable or by infrared transmitter.

Mouse - a pointing device that helps a user navigate through a graphical computer interface. Connected to the computer by a cable, it is generally mapped so that an on-screen cursor may be controlled by moving the mouse across a flat surface. Two common types of mouse, the Microsoft mouse (bottom) and the Apple ADB (Apple Desktop Bus) mouse (top).

It is popularized by Apple Macintosh.

Light pen - a stylus with a light sensitive tip that is used to draw directly on a computer's video screen or to select information on the screen by pressing a clip in the light pen or by pressing the light pen against the surface of the screen. The pen contains light sensors that identify which portion of the screen it is passed over.

The light pen doesn't require a special screen or screen coating, as does a touch screen, but its disadvantage is that holding the pen up for an extended length of time is tiring to the user.

Joystick - a pointing device composed of a lever that moves in multiple directions to navigate a cursor or other graphical object on a computer screen.

Trackball - basically an inverted mouse; the user rotates the ball itself while clicking nearby buttons. Trackball users argue the device is more efficient because it is stationary and saves arm movement; however, many mouse users are uncomfortable with the different style of input.

SOURCE DATA AUTOMATION
Objective: to input data with minimal human intervention. These technologies speed up data collection, reduce errors, and can gather data at the source of a transaction or other event.

Cash Transaction Devices – devices that are common in association with cash transactions.

1. Automated Teller Machine (ATM) - interactive input/output devices that enable people to make bank transactions from remote locations.
2. Point-of-sale (POS) – computerized cash registers that also can incorporate touch screen technology and bar code scanners. Allow the input of numerous data.
Optical Scanners
1. Bar Code Scanners – scans the black and white bar code lines
2. Optical Mark Reader – can detect the presence of pencil marks
3. Magnetic Character Reader – used in banking industry
4. Optical Character Recognition Software – scans to convert text into digital form
Sensors
Cameras
Voice Recognition Systems


OUTPUT TECHNOLOGIES
External devices that transfer information from the computer's CPU to the computer user.

Monitor or video display screen – used with most computers that display input as well as output. It uses cathode ray tube (CRT) technology to shoot beams of electrons to the screen.
Printers - take text and image from a computer and print them on paper.



MEMORY
Stores data for use by a computer

PRIMARY MEMORY A.k.a Main Memory Stores for very brief periods of time three types of information:
1. data to be processed by the CPU
2. instructions for the CPU as to how to process the data
3. operating system programs that manage various aspects of the computer’s operation

RAM Stands for Random Access Memory. A memory that can be read and written by the microprocessor or any hardware device.

Stores more information than the registers.

When you start most software programs on your computer, the entire program is brought from secondary storage into RAM. As you use the program, small parts of the program’s instructions and data are sent into the registers and then to the CPU.
ROM Stands for Read Only Memory. A memory that contains instructions or data that can be read but cannot be modified.

Non-volatile memory since critical instructions is safeguarded. ROM retains these instructions when the power to the computer is turned off.
CACHE MEMORY Consists of a small, high-speed memory system that holds recently used values. When the CPU makes a request to fetch or store a memory value, the CPU sends the request to the cache. If the item is already present in the cache, the cache can honor the request quickly because the cache operates at higher speed than main memory.

SECONDARY MEMORY Designed to store very large amounts of data for extended periods of time. Can have memory capacity or a gigabyte or more.
HARD DISK Made of a rigid metal, with the read-write head flying just above its surface on a cushion of air to prevent wear.

FLOPPY DISKS - made of flexible plastic with small pieces of a magnetic material imbedded in its surface. The read-write head touches the surface of the disk as it scans the floppy


CD-ROMS - high quality capacity, low cost, and high durability.
MAGNETIC TAPES Used primarily for backup storage. The surface of tape is coated with a material that can be magnetized. As the tape passes over an electromagnet, individual bits are magnetically encoded. Computer systems using magnetic tape storage devices employ machinery similar to that used with analog tape: open-reel tapes, cassette tapes, and helical-scan tapes (similar to video tape).

FLASH DISKS Holds more data than CD-ROMS and floppy. It can hold data as large as hard disks can, depending on its capacity.