$0
The bit pattern 0x00000000 occurs so frequently in machine language
that register $0 is wired to permanently hold it.
That bit pattern represents the integer zero, a very common integer.
It also represents a null, which is used to mark the end of
character strings and some data structures.
The arithmetic/logic unit (ALU) of a processor performs integer arithmetic and logical operations. For example, one of its operations is to add two 32-bit integers. An integer used as input to an operation is called an operand. One operand for the ALU is always contained in a register. The other operand may be in a register or may be part of the machine instruction itself. The result of the operation is put into a general purpose register.
Machine instructions that use the ALU specify four things:
The picture shows a 32-bit addition operation.
The operands come from register $8 and from register $9.
The result is put in register $10.
Here is how that instruction is
written as assembly language:
addu $10,$8,$9
Here is another instruction that involves the ALU, written as assembly language:
subu $25,$16,$17
Identify the following: