Computer Fundamentals and Hardware

What a computer does

A computer is an electronic machine that accepts input, processes it according to stored instructions, produces output and stores data for later use. Hardware is the physical equipment; software is the set of instructions that tells the hardware what to do.

Generations of computers

Types of computers

• By working principle: analog (continuous quantities), digital (discrete 0s and 1s), hybrid (both).
• By size and power: microcomputer, minicomputer, mainframe, supercomputer. Banks traditionally ran central processing on mainframes; supercomputers are used for weather and scientific work.

The CPU

The Central Processing Unit is the brain of the computer. Its parts are:

1. Arithmetic Logic Unit (ALU): performs calculations and comparisons.
2. Control Unit (CU): directs the fetch, decode and execute cycle and coordinates other units; it does not process data itself.
3. Registers: very small, very fast storage inside the CPU.

CPU clock speed is measured in hertz (MHz, GHz).

Memory hierarchy and units

From fastest, smallest and costliest per bit to slowest, largest and cheapest:

Registers, then cache, then main memory (RAM), then secondary storage (SSD, hard disk), then offline backup media.

• RAM is volatile: contents are lost when power goes off.
• ROM is non-volatile and holds start-up instructions. Variants: PROM (written once), EPROM (erased with ultraviolet light), EEPROM (erased electrically; flash memory is of this family).
• Cache is a small, fast memory between the CPU and RAM that holds frequently used data.

The table uses the binary convention followed in exams and in memory sizing. Strictly, SI prefixes mean powers of 1000, and the IEC names kibibyte, mebibyte and gibibyte were approved in 1998 for the powers of 1024.

Input, output and storage devices

• Input: keyboard, mouse, scanner, microphone, barcode reader, MICR (reads magnetic-ink characters on cheques), OCR (reads printed text), OMR (reads marks on answer sheets).
• Output: monitor, speaker, plotter, printer. Impact printers (dot matrix) strike a ribbon; non-impact printers (inkjet, laser) do not.
• Both input and output: touch screen.
• Storage: hard disk (magnetic), CD and DVD (optical), SSD and pen drive (flash, no moving parts).

Number systems

Worked examples:

• Binary to decimal: 101101 = 32 + 0 + 8 + 4 + 0 + 1 = 45.
• Decimal to binary: 25 = 16 + 8 + 1, so 25 = 11001. (Repeated division by 2 gives remainders 1, 0, 0, 1, 1 read bottom-up.)
• Binary to hexadecimal: group in fours from the right. 1010 1111 = AF = 10 x 16 + 15 = 175.
• Octal to binary: write each digit as three bits. Octal 57 = 101 111 = 101111 (decimal 47).

Exam pointers

• Vacuum tube, transistor, IC, microprocessor: match each to the first four generations in that order.
• The ALU calculates and compares; the CU controls; registers hold data inside the CPU.
• RAM is volatile, ROM is non-volatile; EPROM is erased by ultraviolet light.
• 1 nibble = 4 bits, 1 byte = 8 bits, and each larger unit is 1024 times the previous one in the binary convention.
• MICR is the cheque-reading device used in banking; OMR reads marks, OCR reads text.
• One hexadecimal digit equals four binary digits; one octal digit equals three.