Where Does the CPU Store its Computations?

The CPU, also known as the processor, is the most critical part of a computer that processes all instructions received from the hardware and software running on the computer. It is also responsible for the retrieval and execution of instructions and all the other computing operations. If you refer to the CPU as the “brain” of the computer, it won’t be wrong. Without a CPU, we cannot run programs and perform any tasks on a computer. So, you have to make sure that it works properly without lagging in any of the situations. 

As we all know, the CPU is responsible for reading data and instructions from memory and then storing the results. So the CPU performs multiple computations in a second. You must know where does the CPU store its computations to better know it. This may be a difficult task but we’re here to make it easy. In this article, we’ll discuss where the CPU stores computations and give an overview of what exactly “compute” is. We’ll delve into the instruction cycle and its components while explaining what RAM is and its role in the process.

What is a computation? 

By definition, computation is just the act of mathematical calculation, since basically all CPUs are digital processors. When you give a CPU instruction, the CPU processes the instruction and stores the outputs as a string of 1s and 0s – binary code. In addition, the CPU consists of logic gate transistors with two values, yes and no which is another way to look at the 1s and 0s. The way binary code is converted is that yes means one, no means zero – binary code is the basic language of computers.

Where does the CPU store its computations? 

You may have heard that the RAM and cache stores the instructions for the CPU, which is true. But there is another type of storage where the CPU stores its instructions and we’ll know about exactly the same memory. Let’s face it, this is a very niche problem, so it’s probably in a computer science test somewhere. That’s probably all you need to know to get through the question, but if you’re interested, we’ll explain it further because there are more factors at play. The CPU utilizes things called registers to store its computations. This can be used as a form of temporary memory for the CPU – very fast, but also very small.

What’s the difference between registers and cache? 

The difference is that registers are built closer to the CPU and are only used to store and retrieve specific information. Unlike caches, registers can be accessed multiple times per clock cycle. You can think of registers as something that sits before the CPU cache.

To understand these differences further, we need to briefly explain what a CPU cache is.

Cache  

A CPU cache is a type of volatile memory, volatile means it erases what is stored in it when power is lost. The opposite applies to non-volatile memory. This type of memory does not forget data until it is overwritten. The cache is built close to the CPU cores for speed and easy access. The cache usually consists of three levels, L1 cache, L2, and L3—there may be a single-level cache in some processors. Anyhow, all three levels have specific functions, and they are configured differently. This is temporary storage that the CPU uses to enter and fetch data it may need again.

Level 1: Cache at this level has the smallest capacity but the fastest speed. This is where critical CPU instructions are stored for faster access.

Level 2: The second cache level is a nice middle ground, with moderate capacity and moderate speed. This is where less important CPU instructions are stored but will still benefit from fast access speeds.

Level 3: The third and last cache level is there with the highest capacity but is much slower compared to the other levels. This is where frequently used paths, such as application paths, are stored to increase CPU usage when accessing frequently used data.

Registers 

The level of the register is lower than that of the cache, which can be considered the L0 cache level. Registers are much smaller and faster than L1 cache. Most of the data registers can hold only a few calculations and partial results. For example, when multiplying, registers will store intermediate results and calculations while the CPU is calculating until it gets to the final result.

Both registers and caches are very important, without either of them, the CPU would be very slow and inefficient. For now, you can consider the register as faster cache memory. 

How does a register work?

Registers are basically not the direct memory part, instead, they are special auxiliary memory locations that provide speed benefits over the actual cache. They work by holding, transferring, and performing arithmetic comparisons at high speed under the direction of the control unit. When the CPU is instructed to perform calculations, it retrieves data from larger memory and stores them in registers for easy access. So these are freed when a new computation is started. In addition, the function can be determined according to the class of the register. 

What are the types of registers?

Not all registers store calculations and similar values. They are divided into seven different categories based on their utility in processing. Let’s look at each of them:

Accumulator: An accumulator is a basic and frequently used register that is a type of data storage memory. These vary in number among the various processors.

Memory Address Registers (MARs): As the name suggests, these registers store the memory addresses used to fetch data to the CPU. Typically, these are parallel load registers that primarily hold the next memory address that needs to be manipulated.

Memory Data Register (MDR): This register stores the data that needs to be written or fetched from a given location. Also known as a memory buffer register, it is used to store data for the next clock cycle.

General Purpose Registers (GPRs): Modern CPUs have GPRs for storing temporary data during ongoing operations. The information stored in these registers can be accessed by the assembler.

Program Counter (PC): As the name suggests, this register keeps track of program execution by holding the address of the next instruction. Sometimes, it also has a function to count the number of instructions.

Instruction Register (IR): PC holds the address of the next instruction, and IR holds the instruction to be processed. Instructions from the PC are fetched from memory and stored in the IR so that the CPU starts executing when the PC points to the next instruction.

Condition Code Register (CCR): Stores the current value of the condition code. It has five flag bits, which are set by the ALU (Logical Arithmetic Unit) to hold information about the operation just performed. These can be carry (C), overflow (V), zero (Z), negation (N), and extension (X).

Role of RAM in CPU Computation

RAM is the separate temporary hardware storage used to store operating system files and other applications. It takes those files or instructions from the storage devices like SSDs, HDDs, or other secondary storage to reduce buffering time and ensure smooth performance. Caches and registers are the internal memory of the processor or CPU, while RAM is external memory but all stores instructions. Therefore, the CPU does not use RAM to store computations. However, it retrieves larger data that would otherwise be accessed again and again. All in all, RAM does the same job as cache.

Conclusion

A processor is an integral part of the computer since it supervises all ins and outs of the system. You must know how does the CPU store its computations so you could better know its working and importance. For your information, the CPU computations are stored exclusively in registers. However, you wouldn’t say that computations are stored too far in the CPU cache as that also plays a vital role. Your CPU needs registers to save and fetch small amounts of data very quickly. It also requires different cache levels to hold data, since these cache levels have much higher capacity than registers.

The difference between the two is that the registers are faster and closer to the actual chip so they are also important for the processor to operate. The similarity is that they are both faster than RAM and integrated closer to the CPU. Also, they both reside in the actual CPU itself. But the caches are larger and slower than registers, which is why registers are used to store the most important data needed for operations. Registers typically store data or instructions that the CPU can use to accomplish its tasks. Your CPU needs registers and caches to be as fast and efficient as possible.

Arslan Ashraf
Arslan Ashraf is Computer Expert. He developed his passion for reviewing the latest tech products. He likes to review every single piece of Hardware. If you have any questions related to Tech Products. He'll be happy to answer you.