Diagram of the computer memory hierarchy

The hierarchical arrangement of storage in current computer architectures is called the memory hierarchy. @@@ main@@@ - title Hierarchy@@@ keywords structure; sociology; information@@@ review@@@ - Computer data storage, often called storage or memory, refers to Computer components devices and recording media that retain digital In Computer engineering, computer architecture is the conceptual design and fundamental operational structure of a Computer system It is designed to take advantage of memory locality in computer programs. In Computer science, locality of reference, also known as the principle of locality, is the phenomenon of the same value or related storage locations Computer programs (also software programs, or just programs) are instructions for a Computer. Each level of the hierarchy has the properties of higher speed, smaller size, and lower latency than lower levels. Speed is the rate of motion, or equivalently the rate of change in position often expressed as Distance d traveled per unit of Latency is a time delay between the moment something is initiated and the moment one of its effects begins or becomes detectable

Most modern CPUs are so fast that for most program workloads, the locality of reference of memory accesses and the efficiency of the caching and memory transfer between different levels of the hierarchy are the practical limitation on processing speed. In Computer science, locality of reference, also known as the principle of locality, is the phenomenon of the same value or related storage locations In Computer science, a cache (kæʃ like "cash") is a collection of data duplicating original As a result, the CPU spends much of its time idling, waiting for memory I/O to complete.

The memory hierarchy in most computers is:

• Processor registers – fastest possible access (usually 1 CPU cycle), only hundreds of bytes in size
• Level 1 (L1) cache – often accessed in just a few cycles, usually tens of kilobytes
• Level 2 (L2) cache – higher latency than L1 by 2× to 10×, often 512 KiB or more
• Level 3 (L3) cache – (optional) higher latency than L2, often several MiB
• Main memory (DRAM) – may take hundreds of cycles, but can be multiple gigabytes. In Computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International A mebibyte (a contraction of me ga bi nary byte) is a unit of Information or Computer storage, abbreviated MiB. Computer data storage, often called storage or memory, refers to Computer components devices and recording media that retain digital Access times may not be uniform, in the case of a NUMA machine. Non-Uniform Memory Access or Non-Uniform Memory Architecture ( NUMA) is a computer memory design used in Multiprocessors where the memory access
• Flash Memory – faster than disk storage, with up to 4GB or more of data, transferring (usually) over universal serial bus (USB)
• Disk storage – millions of cycles latency, but very large
• Tertiary storage – tape, optical disk (WORM)

Management

Modern programming languages mainly assume two levels of memory, main memory and disk storage, though in assembly language, and in inline assembler in languages such as C, registers can be directly accessed. Disk storage is a general category of a Computer storage mechanisms in which data is recorded on planar round and rotating surfaces ( disks, discs, or Computer data storage, often called storage or memory, refers to Computer components devices and recording media that retain digital A programming language is an Artificial language that can be used to write programs which control the behavior of a machine particularly a Computer. See the terminology section below for information regarding inconsistent use of the terms assembly and assembler In Computer programming, the inline assembler is a feature of some Compilers that allows very low level code written in assembly to be embedded in a tags please moot on the talk page first! --> In Computing, C is a general-purpose cross-platform block structured Taking optimal advantage of the memory hierarchy requires the cooperation of programmers, hardware, and compilers (as well as underlying support from the operating system):

• Programmers are responsible for moving data between disk and memory through file I/O.
• Hardware is responsible for moving data between memory and caches.
• Optimizing compilers are responsible for generating code that, when executed, will cause the hardware to use caches and registers efficiently. Compiler optimization is the process of tuning the output of a Compiler to minimize or maximize some attribute of an Executable computer program

See also

• Virtual memory