Instruction Cycle

A program residing in the main memory of a computer contains a sequence of instructions. The CPU executes these instructions by completing a cycle for each instruction. In a primary computer, each cycle for instruction consists of the following steps:

1. Fetch the instruction from memory.
2. Decode the instruction.
3. Read the effective address from memory.
4. Execute the instruction.

Input-Output Configuration

In computer architecture, input-output devices act as an interface between the user and the computer. Below is a Block diagram for the input-output configuration for a basic computer

• is The input and output terminals send and receive information, respectively.
• The information transferred through the input unit will always have eight bits.
• The information generated by the input unit, i.e., the keyboard, is transferred into an input register, ‘INPR.’
• The printer’s information is stored 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., the keyboard, and transmits it to INPR serially.
• The receiver interface receives information from the output register (OUTR) and serially sends it to the printer.

Design of a Basic Computer

A primary computer consists of the following hardware components

1. A memory unit with 4096 words, each word size is 16.
2. 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).
3. Flip-Flops: I, S, E, R, IEN, FGI, and FGO
4. Two decoders: a 3 x 8 operation decoder and 4 x 16 timing decoder
5. A 16-bit common bus
6. Control Logic Gates
7. The logic and adder circuits are connected to the input of AC.

Note: FGI and FGO are considered as control flip-flops.