Processor registers, are the fastest memory with the least amount of space. Most direct computation on modern computers occurs with source and destination operands in registers before being updated to the cache, main memory and virtual memory if needed. On a processor core, there are typically on the order of hundreds of bytes or fewer of register availability, although a register file may contain more physical registers than architectural registers defined in the instruction set architecture. Cache memory is the second fastest, and second smallest, available in the memory hierarchy. Caches are present in processors such as CPUs or GPUs, where they are typically implemented in static RAM, though they can also be found in peripherals such as disk drives. Processor caches often have their own multi-level hierarchy; lower levels are larger, slower and typically shared between processor cores in multi-core processors. In order to process operands in cache memory, a processing unit must fetch the data from the cache, perform the operation in registers and write the data back to the cache. This operates at speeds comparable (about 2-10 times slower) with the CPU or GPU's arithmetic logic unit or floating-point unit if in the L1 cache. It is about 10 times slower if there is an L1 cache miss and it must be retrieved from and written to the L2 cache, and a further 10 times slower if there is an L2 cache miss and it must be retrieved from an L3 cache, if present. Main physical memory is most often implemented in dynamic RAM (DRAM). The main memory is much larger (typically gigabytes compared to ≈8 megabytes) than an L3 CPU cache, with read and write latencies typically 10-100 times slower. , RAM is increasingly implemented on-chip of processors, as CPU or GPU memory. Paged memory, often used for virtual memory management, is memory stored in secondary storage such as a hard disk, and is an extension to the memory hierarchy which allows use of a potentially larger storage space, at the cost of much higher latency, typically around 1000 times slower than a cache miss for a value in RAM. While originally motivated to create the impression of higher amounts of memory being available than were truly available, virtual memory is more important in contemporary usage for its time-space tradeoff and enabling the usage of virtual machines. Cache misses from main memory are called page faults, and incur huge performance penalties on programs.
Processor registers, are the fastest memory with the least amount of space. Most direct computation on modern computers occurs with source and destination operands in registers before being updated to the cache, main memory and virtual memory if needed. On a processor core, there are typi?cally on the order of hundreds of bytes or fewer of register availability, although a register file may contain more physical registers than architectural registers defined in the instruction set architecture. Cache memory is the second fastest, and second smallest, available in the memory hierarchy. Caches are present in processors such as CPUs or GPUs, where they are typic,ally implemented in static RAM, though they can also be found in peripherals such as disk drives Processor caches often have their own multi-level hierarchy; lower levels are larger, slower and typically shared between processor cores in multi-core processors. In order to process operands in cach.e memory, a processing unit must fetch the data from the cache, perfo?rm the operation in registers and write the data back to the cache. This operates at speeds comparable (about 2-10 times slower) with the CPU or GPU's arithmetic logic unit or floating-point unit if in the L1 cache. It is about 10 times slower if there is an L1 cache miss and it must be retrieved from and written to the L2 cache, and a further 10 times slower if there is an L2 cache miss and it must be retrieved from an L3 cache, if present. Main physical memory is most often implemented in dynamic RAM (DRAM). The main memory is much larger (typically gigabytes compared to ≈8 megabytes) than an L3 CPU cache, with read and write latencies typically 10-100 times slower. , RAM is increasingly implemented on-chip of processors, as CPU or GPU memory. Paged memory, often used for virtual memory manag.ement, is memory stored in secondary storage such as a hard disk and is an extension to the memory hierarchy which allows use of a potentially larger storage space, at the cost of much higher latency, typically around 1000 times slower than a cache miss for a value in RAM. While .originally motivated to create the impression of higher amounts of memory being available than were truly available, virtual memory is more important in contemporary usage for its time-space tradeoff and enabling the usage of virtual machines. Cache misses from main memory are called page faults, and incur huge performance penalties on programs.