CHAPTER 4: COMPUTER HARDWARE
4.1 INPUT DEVICES
- Definition: Hardware components used to enter data and instructions into the computer for processing.
- Keyboard: Primary text entry device. Classification of keys: Alphanumeric keys (letters A-Z, numbers 0-9), Numeric Keypad (for rapid number entry), Function Keys (F1-F12, for special software commands), Control Keys (Ctrl, Alt, Shift), and Cursor Control Keys (arrows, Home, End).
- Mouse: A pointing device used to control the cursor on the screen. Functions: Pointing, clicking (selecting), double-clicking (opening), dragging, and scrolling (using the wheel).
- Light Pen: A pointing device sensitive to light, used to draw or select objects directly on the monitor screen (now largely obsolete).
- Scanner: Converts hardcopy documents, photos, or images into a digital format that can be stored and manipulated by the computer.
- Joystick: A stick with a base used to control movement in gaming and simulation applications.
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4.2 OUTPUT DEVICES
- Definition: Hardware components used to display or present processed data (information) to the user.
- Monitors (VDU): Primary output device for soft-copy (non-permanent, on-screen) visual output.
- Printers: Devices that produce hard-copy (permanent, paper) output.
- Inkjet Printers: Spray tiny droplets of liquid ink onto the paper. Good quality, low initial cost, but high running cost for high volume. Slower than laser.
- Laser Printers: Use a laser beam and dry powdered ink (toner) to fuse the image onto the paper. Fast, high quality, and economical for high-volume office use.
- Line Printers: Print an entire line of text at a time. Very fast, primarily used for large reports or industrial tasks.
- Speakers: Convert digital audio signals into audible sound output.
- Plotters: Specialized output devices used to produce high-quality, large-scale vector graphics such as architectural blueprints, maps, and engineering drawings.
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| Characteristic | Input Devices | Output Devices |
| Direction of Data | Into the CPU | Out of the CPU |
| Example Function | Enter data, select commands | Display results, print documents |
| Type of Copy | N/A | Soft copy (Monitor), Hard copy (Printer) |
4.3 CENTRAL PROCESSING UNIT (CPU)
- Definition: Often called the microprocessor or the “brain” of the computer. It executes instructions, performs calculations, and manages all system operations.
- Components:
- Arithmetic Logic Unit (ALU): Performs all arithmetic operations (addition, subtraction, multiplication, division) and logical operations (comparisons like equals to, greater than, AND, OR, NOT).
- Control Unit (CU): The manager of the CPU. It fetches instructions from memory, decodes them, and directs all other parts of the computer (ALU, memory, I/O devices) on what to do.
- System Unit: The main box that houses the CPU chip, the motherboard, power supply, main memory, and other essential components.
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4.4 MEMORY UNIT
- Primary Memory (Main Memory): Directly accessible by the CPU, fast, and expensive.
- RAM (Random Access Memory): Volatile (data is lost when power is turned off). It is the computer’s working memory; holds programs and data currently being used.
- ROM (Read Only Memory): Non-Volatile (data is retained when power is off). Stores permanent, essential system software like the BIOS (Basic Input/Output System) needed to boot the computer.
- Secondary Memory (Auxiliary Storage): Slower, cheaper, and non-volatile. Used for permanent, long-term storage of files and programs.
- Examples: Hard Disk Drive (HDD) (magnetic disks), Solid State Drive (SSD) (flash memory, faster than HDD), CD/DVD-ROM (optical media), Flash Drive/Pen Drive.
- Storage Units:
- Bit (b): The smallest unit (0 or 1).
- Byte (B): 8 bits.
- Kilobyte (KB): 1024 bytes.
- Megabyte (MB): 1024 KB.
- Gigabyte (GB): 1024 MB.
- Terabyte (TB): 1024 GB.
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| Memory Type | Volatility | Speed | Function/Use |
| RAM | Volatile (data lost when power off) | Very Fast | Temporary workspace for current tasks |
| ROM | Non-Volatile (data retained) | Fast (Read-only) | Stores BIOS/Firmware (boot instructions) |
| Hard Disk/Flash | Non-Volatile | Slow | Permanent long-term storage of OS and files |
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4.5 LOGIC CIRCUITS
- Logic Gates: The fundamental electronic building blocks of all digital computers. They are circuits that perform a single logical function (Boolean operation) on one or more binary inputs to produce a single binary output.
- Basic Gates:
- AND: Output is 1 only if all inputs are 1.
- OR: Output is 1 if at least one input is 1.
- NOT: Inverts the input (0 becomes 1, 1 becomes 0).
- Alternative Gates: NAND (NOT-AND) and NOR (NOT-OR). These are called universal gates because any other logic gate (AND, OR, NOT) can be constructed using only NAND or only NOR gates.
- XOR (Exclusive OR): Output is 1 only if the inputs are different.
- Uses of Logic Gates: They are used to build complex digital circuits like adders (to perform arithmetic), comparators (to perform logical operations), registers (to store data), and the entire CPU architecture.
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