What do registers do for the cpu

The control units decodes the machine instruction stored into the instruction register as per the instruction format. The program counter register PC is a special purpose register used by the CPU to store the address of the next instruction to be executed. The program counter register is automatically incremented by one after the fetching the last instruction so that it always points to the address of the next instruction.

A program counter is also alternately referred to as an instruction counter, instruction pointer, instruction address register or sequence control register. In order to execute the program, the CPU repetitively performs the instruction cycle. The fetch operation is the first step of the instruction cycle.

The instructions are stored into the main memory RAM. The CPU fetches these instructions one by one. The program instruction is stored into the instruction register after it is fetched by the CPU.

It is the control unit that decodes the program machine instruction. The control unit decodes the instruction as per the instruction format. The instruction format typically has three parts. The operand part indicates either data or the address of the data.

The opcode stands for operation code that defines the operation to be performed and the addressing. The addressing mode part of the instruction format defines the either direct referencing or indirect referencing. For indirect referencing , the operand value contains the memory address or effective address of the operand.

The accumulator register is used by the ALU arithmetic and logic unit to perform the arithmetic and the logical operations performed by the CPU. The ALU operates on the data stored into the accumulator register. A CPU organization is said to be a single accumulator type when it has only one single accumulator. The memory address register MAR is also called as address register.

The memory address register MAR essentially contains the memory address from where the CPU either needs to fetch the data or write the data. During the program execution, the CPU performs the memory read and write operations at specific memory address.

This address is stored in the MAR. The memory address register is used by the CPU while performing the input and output operations. The memory address register specifies the memory address either for memory read or memory write operation. The memory buffer register MBR is also called as data register. It essentially contains the data that CPU either has to fetch from the memory. This data is stored in the MBR. The memory buffer register is used by the CPU while performing the input and output operations.

The memory buffer register stores the data fetched by the CPU during the memory read operation or the data for memory write operation. In some programs the user inputs the data that is processed by the computer. In computer architecture this data is temporarily stored into the input register. The input register INPR is a 8 bit register that stores the alphanumeric input data. The contents of the input register is transferred to the accumulator AC where ALU operates on the data.

Similarly , the CPU operates on the program data as per the program instructions. The processed data is stored in the output register OUTR. The data from the output register is then sent to the main memory RAM.

The operating system then sends the data to the output device. The temporary registers are general purpose registers used by the CPU during the program execution to temporarily store the data. This is the most comprehensive and unique C omputer Science And Programming Fundamentals course Online which will give you in depth understanding of most important fundamental concepts in computer science And Programming.

Home About Course Contents 1. Introduction To Computer Science 2. Thus the number of the register that is available in the CPU and how large is our instructions will be significantly impacting the time of execution of our code.

This having adequate CPU register will help in faster and smooth execution. Here we discuss an introduction to CPU Register, operations, different types, uses, advantages and disadvantages. You can also go through our other related articles to learn more —. Submit Next Question. By signing up, you agree to our Terms of Use and Privacy Policy.

Forgot Password? This website or its third-party tools use cookies, which are necessary to its functioning and required to achieve the purposes illustrated in the cookie policy.

By closing this banner, scrolling this page, clicking a link or continuing to browse otherwise, you agree to our Privacy Policy. Popular Course in this category. Course Price View Course. Free Software Development Course.

Login details for this Free course will be emailed to you. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only. Registers are typically addressed by mechanisms other than main memory, but may in some cases be memory mapped. 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. Jeroen Jeroen 1 1 gold badge 7 7 silver badges 13 13 bronze badges.

CPU level-1 cache is often made of the same type of silicon stuff as registers. It is not quite as fast because it needs extra lookups to associate cached addresses with cache locations.

But registers and cache are definitely different places on the chips. JimmyHoffa: I'm afraid that your comment will be very confusing to OP, to the detriment of computer science knowledge. And another difference is size: a register file is rarely larger than a couple of hundreds of words, while L1 cache can easily be something as large as 64k.

Show 5 more comments. Active Oldest Votes. EDIT: Here's a simple explanation for how register logic works. Improve this answer. Mason Wheeler Mason Wheeler And more stuff in the warehouse across town disk and other stuff he can have Fedex'd in network :- — Dan Pichelman.

Depends very heavily on the system architecture in question. Binero in a 16 bit x86 processor you have registers named Ax, Bx and so on. In 64 bit mode they named the registers RAx with the lower 32 bits being EAx and the lower 16 bits still being Ax. And in modern CPUs, this kinda breaks down, as well, due to the registers being merely temporary mappings to an in-core bank of Really Fast Memory, changing depending on the instruction stream and how closely it is following the predicted instruction stream.

MasonWheeler A good choice on your part. Show 10 more comments. You can see Mason Wheeler explanation for exaples. Add a comment. I think it helps to think that Registers are not memory and should not be thought of as such.