What is the register? How many types of registers and what are they?

Register

The register is a FF or memory element group, which works to store digital information together. It stores data in binary system. An FF can store one bit of digital data. The number of FFs needed to store a word depends on the number of bits in that word. For example, a group of 8 FFs is required to store a word of 8 bits. Thus, registers are groups of FFs or memory elements that work together to store digital information. In various digital systems, such as-

 (i) Microprocessors of computers 

(ii) Arithmetic and logic circuits. 

Types of Registers: Registers are divided into different categories according to the type of work. Such as—

(i) Temporary registers, 

(ii) Flag registers, 

(iii) General purpose registers are of 2 types based on providing inputs and outputs, namely— 

(i) Serial and 

(ii) Parallel.

Four types according to data shifting or mode, namely : (i) SISO (ii) SIPO (iii) PISO (iv) PIPO Based on data shifting it is three types, namely : (i) Left Shift (ii) Right Shift ( iii) Bidirectional or universal shift.

Structure of Register: Serial-In Serial-Out (SISO) Register: The registers in which data enters serially and is output serially are called Serial-In Serial-Out (SISO) registers. Four D-type FFs are added to transfer four bits of data. FFS must be reset by a signal before entering data. The data to be entered into the register is first fed to the input of FF and is shifted sequentially in the form of a right shift by clock pulses. And the output is taken from the last FF.