1 How Computers Work

A computer works in three stages: It accepts input (through the input devices), then processes it (CPU) and gives us the output (through output devices).

1.1 Computer Hardware:

• Hardware refers to the physical parts of the computer and related devices. Hardware is used to run or interact with the software.
• Internal devices include the hard drive, motherboard, video and sound cards.
• External devices include the monitor, printer, scanner, keyboard, and mouse.
• Removable storages such as a USB flash drive, CD, or DVD Rom are also examples of hardware.
• External devices of a computer are also called peripheral devices.
• Computer hardware can be classified into input, output, storage, and processing devices.

1.1.1 Input Devices

• Input devices such as a keyboard or mouse permit users to communicate with the computer.
• Input devices: Keyboard – pointing devices (mouse, joystick) – voice input devices – digital camera – scanning devices

1.1.2 Output Devices

• Output can be in the form of a soft copy or hard copy.
• Output devices: Visual display unit (monitor, projector, LCD) – Speaker and Headset – Plotter – Printer (impact, non-impact)
• The display and printer are output devices through which a computer makes processing results visible to the user.
• A disk drive is both an input and an output device because it can either provide stored information or store it after processing.

1.2 Computer Memory and Storage Devices

1.2.1 Bit and Byte:

• Computer memory is a mechanism that stores data for use by a computer.
• In a computer, all data consists of numbers.
• A computer stores a number into a specific location in memory and later fetches the value.
• Most memories represent data with the binary number system.
• Binary digits or bits have two possible representations (“0” and “1”, or ‘off’ and ‘on’).
• If a second bit is added to a single bit of information, the number of representations is doubled, resulting in four possible combinations: 00 – 01 – 10 – 11.
• A third bit added to this two-bit representation again doubles the number of combinations, resulting in eight possibilities. 000 – 001 – 010 – 011 – 100 – 101 – 110 – 111.
• Each time a bit is added, the number of possible patterns is doubled.
• An Eight-bit combination is called a byte; a byte has 256 possible combinations of 0s and 1s.
• A byte is a useful quantity to store information because it provides enough possible patterns to represent the entire alphabet, in lower and upper cases, numeric digits, punctuation marks, and several character-sized graphic symbols., including non-English characters.
• A byte can also be interpreted as a pattern representing a number between 0 and 255.
  • A kilobyte is equal to 1,024 bytes and can store about 1,000 characters.
  • A megabyte can store about 1 million characters.
  • A gigabyte can store about 1 billion characters.
  • A terabyte can store about 1 trillion characters or 1,024 GB.

Computer memory may be divided into two broad categories: internal memory and external memory

1.2.2 Internal Memory or Primary Memory:

• Internal memory processes at the highest speed and can be accessed directly by the central processing unit.
• Internal memory is contained on computer chips and uses electronic circuits to store information. ROM, RAM, etc., are examples of internal memory.

1.2.2.1 Read-Only Memory (ROM)

• ROM is a memory containing hard-wired instructions that the computer uses when it boots up.
• Before the system software loads on the computer, the instructions are read from a small program in the ROM called “BIOS.”
• The data in the ROM is permanent.
• The CPU can only read the ROM, which cannot be changed.
• ROM is non-volatile memory.