A program residing in the main memory of a computer contains a sequence of instructions. These instructions executed by the CPU by completing a cycle for each instruction.
In a basic computer, each cycle for instruction consists of the following steps:
- Fetch the instruction from memory.
- Decode the instruction.
- Read the effective address from memory.
- Execute the instruction.
In computer architecture, input-output devices act as an interface between the user and the computer. A Block diagram for the input-output configuration for a basic computer, given below.
- The input and output terminals send and receive information respectively.
- The amount of information transferred through the input unit will always have eight bits.
- The information generated by the input unit i.e. keyboard is transferred into an input register ‘INPR’.
- The information for the printer is store in the output register ‘OUTR’.
- Registers INPR and OUTR communicate with each other serially through AC. But AC works parallel.
- The transmitter interface gets the information from the input unit i.e. keyboard and transmits it to INPR serially.
- The receiver interface receives information from the output register (OUTR) and sends it to the printer serially.
Design of a Basic Computer
A basic computer consists of the following hardware components.
- A memory unit with 4096 words and size of each word is 16.
- Registers: AC (Accumulator), DR (Data register), IR (Instruction register), PC (Program counter), AR (Address register), TR (Temporary register), SC (Sequence Counter), INPR (Input register), and OUTR (Output register).
- Flip-Flops: I, S, E, R, IEN, FGI, and FGO
- Two decoders: a 3 x 8 operation decoder and 4 x 16 timing decoder
- A 16-bit common bus
- Control Logic Gates
- The Logic and Adder circuits which are connect with the input of AC.
Note: FGI and FGO are consider as control flip-flops.