Registers

2. Definition

A register is an extremely fast form of hardware memory residing in a microprocessor or microcontroller. The 'width' of a register is defined by how many binary bits it can store. For example an 8 bit register holds 8 binary digits, each one being a 0 or a 1.

Registers have a number of functions depending on their design. These include

• holding temporary data whilst processing is underway, for example the Accumulator in a microprocessor
• to hold machine status bits, for example the Program Status Word register holds the instantaneous state of the computer. The currently running software can access this to check on the state of the machine
• to hold the next instruction to be executed within the processor, for example the instruction register
• to handle data flowing in and out of RAM, for example the MDR and MAR registers within a processor
• To handle inputs and to set outputs, for example the IO control registers in a microcontroller.

So you can see that registers have a vital role to play within many digital devices.