CPU cache is a type of RAM built into a microprocessor for immediate memory access, improving performance. L1 and L2 caches are common, with L3 also available. Cache stores frequently accessed data, improving efficiency. Larger caches can outperform faster processors with less cache. FSB speed also affects performance.
The central processing unit (CPU) cache is a type of random access memory (RAM) that is built directly into a computer’s microprocessor itself and is designated as an L1 cache. Another variety of CPU caches are the limited capacity L2 static RAM (SRAM) chips on the motherboard. Both of these types of memory are accessed first by the microprocessor in executing routine instructions before standard RAM memory is used, which gives the processors improved performance characteristics.
The practice of placing CPU cache memory on microprocessors for immediate memory access in order to speed up data access for the processor has been practiced since the creation of the 80486 computer processor made in 1989, which had an L1 cache register integrated rudimentary. Larger levels of L2 cache that were directly integrated into processor functionality came into use in 1995. As of 2011, there is also a third level of CPU cache memory in some computer systems known as L3, which is accessed before the main RAM memory of the system itself is used. Each cache level is designed to be larger and slower in performance as its distance from the microprocessor increases. Early levels of CPU L1 caches were 8 kilobytes in size, with L2 cache on machines starting in 2007 already exceeding the 6 megabyte limit, and some systems starting in 2011 had an L4 cache buffer built in size up to to 64 megabytes.
The function of high-speed, low-volume cache memory for microprocessors centers on how they execute instructions. When a microprocessor performs operations, it traditionally has to send data requests to main memory over the system bus. In computing terms, this is a very slow process, so CPU designers have created process shortcuts for data that is repeatedly accessed by the microprocessor. When frequently accessed data is already loaded into the CPU cache, the microprocessor can perform operations at a much faster and more efficient rate. For this reason, this central processing unit memory is often referred to as the instruction cache or data cache where it is tied directly to the functionality of the microprocessor and the hardware of the computer itself. In contrast, much of the data stored in a computer’s standard RAM is software caches for the many programs that the computer runs simultaneously.
L1 cache is also often referred to as protected memory or non-write allocated memory, because the data stored in this cache is essential for the computer to function. If it is accidentally overwritten, the computer can experience a general protection fault in which it is forced to shut down and restart to clear the corrupted CPU cache. Various levels of CPU caches have write buffer capabilities, where they will rewrite data stored in main memory to free up space in the cache for when more frequently accessed operations need higher priority processing.
Large amounts of CPU cache will improve the performance of a microprocessor to a point where it can outperform a faster processor that has less cache memory built into the system. The speed of the front-side bus (FSB) is also a determining factor in determining the performance of the microprocessor. Bus speeds in general have traditionally been a bottleneck to performance characteristics on personal computers (PCs) where processing must be piped back and forth across the bus to memory. High FSB rates as of 2011 for Core 2 processors are at a level of 1,600 megahertz, or 1,600 million cycles per second, of computer instruction sets.
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