Simple Hypothetical Computer
A computer accepts inputs from a user and provides the desired output to the user after processing the input data. All the functional components of a computer that process the data are fixed inside the cabinet of a computer. A microprocessor incorporates the functions of a CPU on a single integrated circuit (IC) or on a few integrated circuits. A microprocessor processes the data that is represented in the binary numeral system and produces output as per it is being programmed. Not only computers but also all the digital data processing devices are powered by microprocessors. According to the requirements, the architecture of a microprocessor is designed. A Simple Hypothetical Computer is used as a base to explain the operation of a real computer. It is done in order to understand the essential and universal aspects of a microprocessor. A Simple Hypothetical Computer includes following blocks: ALU, Registers, Interrupt Control, Instruction Decoder, Timing and Control Section. ALU (Arithmetic Logic Unit) is a 8-bit unit that performs all the arithmetical and logical operations. Registers are used to store data (operators, operands, results and addresses) for processing. Interrupt Control executes required steps to handle interruptions from various peripherals attached to a computer. Timing and Control Section generates appropriate signals to control various peripheral devices in order to carry out an instruction.
As an instruction is fetched from the memory, the value of Program Counter gets incremented to point the next instruction. Therefore, instructions are fetched sequentially from the memory. However, control transfer instructions may change the sequence by placing a new value in the PC. Status Word is a collection of flag bits for a processor that contains information about the state of the processor. It includes at least three central flags, namely zero, carry and overflow, which are set or cleared automatically as per the operations performed by the ALU.