Question

what are the uses of large register file in a
RISC ? Explain with the help of a diagram.

Answer 1

Answer:

Explanation:

Use of large Register file in RISC

The register storage is the faster storage device, faster than even the main memory and the cache. Thus, a strategy is needed that will allow the most frequently accessed operands to be kept in registers and to minimize register memory operations.

Two basic approaches are possible, one based on the software and the other based on the hardware. The software approach is to rely on the compiler to maximize register usage. The compiler will attempt to allocate the registers to those variables that will be used most in the given time period. This approach requires the use of sophisticated program-analysis algorithms. The hardware approach is simply to use more registers so that more variables can be held in registers for longer periods of time. RISC follows the hardware approach.

Since most operand references are to local scalars, the obvious approach is to store these in registers, with perhaps a few registers reserved for global variables. The problem is that the definition of local changes with each procedure call and return, operations that occur frequently. On every call, local variables must be saved from the registers into memory, so that the registers can be reused by the called program. Furthermore, the parameters must be passed. On return, the variables of the parent program must be restored and the results must be passed back to the parent program.

RISC takes care of these with the help of register windows. Multiple small sets of registers are used, each assigned to different procedure,. A procedure call automatically switches the CPU to use a different fixed size window of registers, rather than saving registers in memory. Windows for adjacent procedures are overlapped to allow parameter passing

Answer 2

The use of large register file in a RISC are as follows:

• For storing interim results and streamlining operand references, many registers are helpful. Register storage has the advantage over memory storage in that information can be transferred between registers much more quickly with registers than it can to and from memory.
• In contrast to complex instructions, RISC "reduced instructions" use fewer transistors, freeing up more space for general-purpose registers. Pipelining is possible because every instruction completes in exactly one clock's worth of time.
• When the floating-point extension is implemented, RISC-V will have separate 32 floating-point registers in addition to 32 integer registers (or 16 in the embedded variant). Instructions only address registers, with the exception of memory access instructions.

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