Processor
The processor is the brain in the system. It is responsible for executing programs and supervising the functioning of the other parts of the system. The processor is perhaps the most complex element in the system.
Main Memory
Main memory can be split into two categories;
RAM
Or random access memory is used for memory that is readable and writable. It can be implemented in many technologies. RAM is used by the processor to store (write) data and load (read) it back. The contents of RAM is volatile - they are forgotten when the power is turned off
ROM
Read-only memory (ROM) doesn't forget when the power is turned off - the content is not volatile. ROM provides random access like RAM but it cannot be written to once it is set up. It is used to hold fixed programs such as the bootstrap program in a PC.
I/O
To be useful, the CPU needs to communicate with devices known as peripherals.
I/O controller: allows the computer to communicate with peripherals without the CPU knowing how they work.
I/O Ports: its a method of performing inputs and outputs between CPU and peripheral devices in a computer.
Bus
Address
a unidirectional bus, typically consisting of 32 wires, used to address memory and I/O locations
Data
a bidirectional bus, typically consisting of 32 wires, used to transport data between the three components of the three box model
Control
a bidirectional bus, typically consisting of 8 wires, used to transport control signals between the three components of the three box model
