1.4 Overview of Hardware

The computer system consists of the following four main components (Stallings, William, (2011)):

		Processor.
		Main memory.
		I/O devices.
		System bus.

	CPU has buffers called registers to store the data transferred to and from the main memory. Examples of
	these registers are the following:

		Program counter (PC): it has the address of the next instruction to be executed.
		Instruction register (IR): it has the instruction currently executed.
		Memory address register (MAR): it has the address in memory for the next read or write operation.
		Memory buffer register (MBR): it has the data to be used in the read or write operations.
		I/O address register (I/O AR): it has the address of a particular I/O device.
		I/O buffer register (I/OBR): it has the data to be exchanged between an I/O module and the processor.
		Accumulator (AC): A buffer register is used to hold temporary data during execution.

1.4 Overview of Hardware

	CPU executes each program instruction using two cycles. The first cycle is the fetch cycle.
	The PC register has the address of the instruction in the main memory. The second cycle is the execution
	execution cycle which decodes the instruction and executes it.