Processor registers are the fastest memory access on a CPU, storing regularly accessed values. Different types of registers exist, and developers design programs to operate in register memory for faster processing. CPUs search register cache first before examining RAM and hard drives.
The fastest access to storable memory on a computer processing unit (CPU) is a processor register. Computer architectures design the processor register memory capacity into a CPU cache so that values regularly accessed by computer processes can be stored there. Processes can access and run quickly based on those stored values. Because processor registers are stored on the CPU, they are considered the top of the memory storage hierarchy, and allocation is usually determined by variables. Once processed, the data is restored to cache, random access memory (RAM), or hard disk storage.
Computer processors have registers of different types, according to instructions or tests that operate on them or according to their specific content. Data, addresses, and general purpose registers contain math values and addresses for storage in memory. There are conditional registers with truth values for logic operation instructions, constant registers with read-only values like pi and zero, and special purpose registers that maintain a program counter, status register, and stack pointers for memory usage of the stack. Control registers contain instructions from an instruction set built into the CPU architecture; and there are several that fetch from RAM and CPU circuits that access memory buffers, memory data, memory type ranges, and addresses. Variables not assigned to a processor register are stored in RAM and loaded in and out for read and write operations, however, these are slower to process.
Knowing the speed difference between processing in registers and RAM, developers of compiler computer programs usually design their programs to operate as much in processor register memory as possible for functions to run quickly. For just-in-time compiler programs, a register allocation technique known as linear scan allocation tracks register operations and quickly releases register computing power to the program. Register allocation techniques attempt to get the largest number of program variables assigned to registers and in a flow of operations that maximizes the minimum number of registers for fast compilation.
Since many processor registers are for temporary storage of variables and instruction sets, all operations for program use can be stored for manipulation by the CPU. In operation, a CPU will first search the CPU’s register cache for a copy of any data to be processed in read, write, or move operations, before examining RAM and secondary storage on hard drives. As of 2011, most CPUs maintain three individual caches. Instruction caches involve performing fetch operations per instruction, a translation-like buffer speeds address translations for virtual to physical addresses, and a data cache contains a multilevel hierarchical store of data to be manipulated by an processor register instruction set.
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