Q. Total number of registers in a CPU?

Factors to consider when choosing total number of registers in a CPU are: 

• CPU can access registers faster than it can access main memory.
• For addressing a register depending on the number of addressable registers a few bit addresses are required in an instruction. These address bits are definitely quite less in comparison to a memory address. For illustration, for addressing 256 registers you just require 8 bits while the common memory size of 1MB needs 20 address bits which makes a difference of 60%.
• Compilers tend to employ a small number of registers since large numbers of registers are very difficult to use efficiently. A general good number of registers is 32 in a general machine.
• Registers are more costly than memory though far less in number.