Chapter 19: ICT Fundamentals, Data Representation, and Digital Logic

Information and communication technology

Data are raw facts; information is data that have been processed to be meaningful; knowledge is information that has been understood and can be applied. An information system takes inputs, processes them, stores them, and produces outputs. ICT combines computing, communication, and information management, and it shapes every area of life, from education and health to business and government. Its impacts are both positive (access to information, efficiency, new services) and negative (privacy risks, cybercrime, the digital divide, job displacement), and responsible use requires awareness of ethics and law.

Computer organization

A modern computer follows the von Neumann architecture: a CPU (control unit, arithmetic logic unit, registers) fetches instructions and data from memory, executes them, and communicates with input/output devices through buses. The fetch–decode–execute cycle repeats for every instruction. The memory hierarchy runs from fast, small, expensive registers and cache to RAM and then to slow, large, cheap secondary storage (SSD, hard disk). Performance depends on clock speed, number of cores, cache, memory, and the instruction set. Input devices (keyboard, scanner, sensors), output devices (monitor, printer), and storage devices make up the rest of the system, and firmware (BIOS/UEFI) starts the machine.

Number systems and data representation

Computers use binary (base 2). Conversions:

Decimal to binary: divide repeatedly by 2 and read the remainders upward. : , so .

Binary to hexadecimal: group in fours. . Hexadecimal digits go from 0–9 and A–F, so .

Octal groups bits in threes.

Negative integers use two’s complement: invert the bits and add 1. For in 8 bits: ; inverted ; adding 1 gives . An 8-bit two’s complement integer represents to . To add numbers in two’s complement, add as ordinary binary and ignore any carry out of the leftmost bit; overflow occurs when the sign of the result is wrong.

Real numbers are stored in floating-point form (sign, exponent, mantissa), typically according to the IEEE 754 standard, which means that some decimals (like 0.1) cannot be represented exactly and small rounding errors arise.

Text is stored with a code: ASCII (7 bits, 128 characters) or Unicode (UTF-8 and others), which covers all the world’s scripts including Sinhala and Tamil. Images are arrays of pixels; the file size is roughly (width × height × bits per pixel) ÷ 8 bytes before compression. Sound is stored by sampling the waveform at a rate (at least twice the highest frequency, by the Nyquist theorem) with a given number of bits per sample. Example: 1 minute of stereo audio at 44.1 kHz and 16 bits is MB uncompressed. Compression is lossless (ZIP, PNG) or lossy (JPEG, MP3).

Boolean algebra and logic gates

The basic gates are AND (), OR (), NOT (), and the derived NAND, NOR, XOR (), and XNOR. NAND and NOR are universal gates; any circuit can be built from either alone.

Laws: , , , ; commutative, associative, distributive laws; absorption ; and De Morgan’s laws:

Example: . Group: , so (absorption of in the second term). So . A Karnaugh map (K-map) simplifies a function visually by grouping adjacent 1s in powers of two.

Combinational and sequential circuits

A half adder adds two bits: Sum , Carry . A full adder adds two bits and a carry-in: Sum , . Chains of full adders form a ripple-carry adder. Other combinational circuits: multiplexers, decoders, and comparators. Sequential circuits have memory. An SR latch and flip-flops (D, JK, T) store one bit; registers and counters are built from flip-flops, and clocks synchronize them.

Common mistakes

Forgetting to specify the number of bits for two’s complement.

Reading remainders from top to bottom in a decimal-to-binary conversion.

Confusing with .

Treating bits (b) and bytes (B) as the same.

Practice questions

Convert to binary and hexadecimal. [11010110₂; D6₁₆]

Represent in 8-bit two’s complement. [11101110]

Simplify . []

Draw a full adder using XOR, AND, and OR gates.