how computer works

A computer in its simplest form comprises five functional
units: the input unit, the output unit, the memory unit, the
arithmetic & logic unit (ALU), and the control unit.
Program execution involves the CPU fetching instructions
sequentially one-by-one from the main memory. The CPU then
decodes the instruction and performs the specified operation
on associated data operands, typically in the ALU. The internal
operation of the computer can be summarized as: Fetch,
Decode, and Execute steps.
An instruction generally consists of two parts: an Operation
code (Opcode) and one or more operands. The Opcode
specifies the operation to be performed, and the operands are
the data or addresses associated with that operation.
The Program Counter (PC) register keeps track of the
execution of the program. It specifically holds the address of
the next instruction to be read from memory after the current
instruction is executed. Instruction words are read and
executed in sequence unless a branch instruction is
encountered.
The ALU performs the actual computation or processing of
data, containing necessary logic circuits (like adders and
comparators) to perform operations such as addition,
multiplication, and comparison. The Control Unit (CU)
coordinates the activities of all units by issuing control signals.
The CU also reads and interprets (decodes) the program
instructions.