Q. Explain about Registers?

A register is a group of flip-flops that store binary information and gates that controls when and how information is transferred to register. An n-bit register contains n flip-flops and stores n-bits of binary information. Two fundamental types of registers are: Shift register and Parallel registers.

A parallel register is one of simplest registers comprising a set of flip-flops which can be read or written concurrently. Figure demonstrates a 4-bit register with parallel input-output. Signal lines I_o to I₃ inputs to flip-flops that may be output of other arithmetic circuits such as multipliers so that data from different sources can be loaded in the register. It has one extra line known as clear line that can clear register completely.  This register is known as a parallel register as all bits of register can be loaded in a single clock pulse.  

Figure: 4-bit parallel register

A shift register is used for shifting data to left or right. A shift register operates in serial input-output mode it implies that data is entered in register one bit at a time from one end of register and can be read from other end as one bit at a time. Figure below demonstrates a 4-bit right shift register employing D logical shift functions.

Figure: 4-bit right - shift register