If you're new to processors, it's easy to understand that "a processor which can process n bits of data at a time is called an n-bit processor". But to understand it more accurately, we need to know about the components that make up a processor.
A processor is not a single element device, but a set of elements that are packed together. These include the control unit, the ALU (arithmetic logic unit) or data processing unit, registers, and the system bus.
When you give an instruction, the control unit generates a control signal. This signal collects data from memory or the outside world and tells the ALU what operation it needs to perform.
The data comes from memory or the outside world and is stored in registers. The ALU then collects the data from the registers, processes it, and sends it back to the registers. Once the data is sent back to memory or the outside world, all communication between memory-to-registers-to-ALU or vice versa is done through the system bus, which is a cable system that has three different lines to pass data, the address of data at memory, and control signals. These are known as the data bus, address bus, and control bus, respectively.
For an ideal n-bit processor, all of these elements should be n bits. However, several manufacturers complicate matters by changing the size of the elements. For example, for a 16-bit processor, some manufacturers use a 20/16-bit address bus, 8/13/14/16-bit registers, and a 16-bit ALU. So how they determine the processor bits.
In determining the processor bits, here are some basic facts to consider:
If the ALU is 16 bits, it can perform operations on 16 bits of data at a time.
If the register is 16 bits, it can store 16 bits of data at a time.
If the data bus is 16 bits, it can pass 16 bits of data at a time.
If the address bus is 16 bits, it can pass 16 bits of the address of data at a time.
Consider the facts for a 16 bits processor : Actually size of the address bus related to memory. If memory size is huge, each data address is also long as so address bus. Higher bits of address bus is used so that processor may work with more big memory storage.
If registers are 8 bits , two combining registers can be used to store 16 bits data.
If ALU is 8 bits , it can't process a 16 bit data at a time need twice. But some manufacture uses extra bits ALU in a 16 bits processor to get faster operation. However, the data path for a 16-bit processor is always 16 bits because you need to transfer data memory-to-registers-to-ALU at a time to process. Therefore, we can say that an n-bit processor means it has an n-bit data path.
