Register File

A small number of fast memory units Lets multiple values be read and written simultaneously (wait whattodo)

• A collection/array of registers
• Each register has an address (a number for the register)
• Depending on the total number of address bits we can handle for reading or writing, say k, then we can have at most 2^k registers!
  • i.e. if k is 5 bits, you can store 32 registers
• Each register also has a certain n-bit width (i.e. each register can hold n-bits of info)
  • Each register might be 64 bits in, say, x86-64
  • In MIPS it’s 32 bits!

Functionality

• We can read two registers with this implementation! Register A and B draw from the Q outputs of all registers and uses a one-hot decoder to get the selected output. This results in n-bit outputs
• For writing we have a n bit input to override a register’s data with.
• For writing we also have a k bit input as well. This is our Destination Reg.
• To know if we are writing we have a WriteEnable input. We don’t need a ReadEnable because we can just decide not to read the data… Reading is trivial. You pass in k bits and that represents the address. You can decode that to select the right register’s output Q and output that. Double that for A and B to read many data simultaneously

As for writing you need write enable true. The destination register address is decoded to enable writing for the specific register. We want to load when WriteEnable and the decoder agree on a register, so we need k AND gates as well. Then the n bit input, passed into all registers, finally gets to change the register value.