Invalid register operand when updating
Modern processors use either static or dynamic RAM as main memory, with the latter usually accessed via one or more cache levels.Processor registers are normally at the top of the memory hierarchy, and provide the fastest way to access data.The term normally refers only to the group of registers that are directly encoded as part of an instruction, as defined by the instruction set.However, modern high-performance CPUs often have duplicates of these "architectural registers" in order to improve performance via register renaming, allowing parallel and speculative execution.Registers are typically addressed by mechanisms other than main memory, but may in some cases be assigned a memory address e.g. Almost all computers, whether load/store architecture or not, load data from a larger memory into registers where it is used for arithmetic operations and is manipulated or tested by machine instructions.Manipulated data is then often stored back to main memory, either by the same instruction or by a subsequent one.
8086/8088, 80186/80188, 80286, with 8087, 80187 or 80287 for floating-point, with an 80-bit wide, 8 deep register stack with some instructions able to use registers relative to the top of the stack as operands; without 8087/80187/80287, no floating-point registers 80386 required 80387 for floating-point, later processors had built-in floating point, with both having an 80-bit wide, 8 deep register stack with some instructions able to use registers relative to the top of the stack as operands.
Processors that have the ability to execute single instruction on multiple data are called vector processors.
A processor often contains several kinds of registers, which can be classified according to their content or instructions that operate on them: Hardware registers are similar, but occur outside CPUs.
Modern x86 design acquired these techniques around 1995 with the releases of Pentium Pro, Cyrix 6x86, Nx586, and AMD K5.
A common property of computer programs is locality of reference, which refers to accessing the same values repeatedly and holding frequently used values in registers to improve performance; this makes fast registers and caches meaningful.