# What is the meaning of “Register.Rd”?

Reading Hennesy's book "Computer Organization and Design" it is mentioned "Register.Rd" and "Register.Rs" but what does it mean? The .Rd, .Rt and .Rs parts I can't understand, on page 365:

They are just generic ways of referring to cpu registers:

• Rd is usually denotes a destination register.
• Rs, Rt usually denote source registers.

For example, a cpu instruction could be:

add Rs,Rt,Rd

Which would mean: Rd = Rs+Rt

The Rd,Rs,Rt are placeholders for the actual registers used in this instruction. A specific example for this instruction could be:

add $1,$2,$3 Which would mean "write the sum of specific cpu registers $1 and $2 into $3".

I'm not very familiar with this exact subject, but within instruction sets tables for microcontrollers these conventions are often used:

• rd : destination register
• rs : first source register
• rt : second source register

This looks quite similar with your quote.