What are registers?
One of a small number of high-speed memory locations in a computer's CPU. Registers differ from ordinary random access memory in several respects: There are only a small number of registers (the "register set"), typically 32 in a modern processor though some, e.g. SPARC, have as many as 144. A register may be directly addressed with a few bits. In contrast, there are usually millions of words of main memory (RAM), requiring at least twenty bits to specify a memory location. Main memory locations are often specified indirectly, using an {indirect addressing} mode where the actual memory address is held in a register. Registers are fast; typically, two registers can be read and a third written -- all in a single cycle. Memory is slower; a single access can require several cycles.
One of a small number of high-speed memory locations in a computer's CPU. Registers differ from ordinary random access memory in several respects: There are only a small number of registers (the "register set"), typically 32 in a modern processor though some, e.g. SPARC, have as many as 144. A register may be directly addressed with a few bits. In contrast, there are usually millions of words of main memory (RAM), requiring at least twenty bits to specify a memory location. Main memory locations are often specified indirectly, using an {indirect addressing} mode where the actual memory address is held in a register. Registers are fast; typically, two registers can be read and a third written -- all in a single cycle. Memory is slower; a single access can require several cycles.
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