Memory hierarchy in the context of Primary memory

Computer data storage or digital data storage is the retention of digital data via technology consisting of computer components and recording media. Digital data storage is a core function and fundamental component of computers.

Generally, the faster and volatile storage components are referred to as "memory", while slower persistent components are referred to as "storage". This distinction was extended in the Von Neumann architecture, where the central processing unit (CPU) consists of two main parts: The control unit and the arithmetic logic unit (ALU). The former controls the flow of data between the CPU and memory, while the latter performs arithmetic and logical operations on data. In practice, almost all computers use a memory hierarchy, which puts memory close to the CPU and storage further away.

Instructions per second (IPS) is a measure of a computer's processor speed. For complex instruction set computers (CISCs), different instructions take different amounts of time, so the value measured depends on the instruction mix; even for comparing processors in the same family the IPS measurement can be problematic. Many reported IPS values have represented "peak" execution rates on artificial instruction sequences with few branches and no cache contention, whereas realistic workloads typically lead to significantly lower IPS values. Memory hierarchy also greatly affects processor performance, an issue barely considered in IPS calculations. Because of these problems, synthetic benchmarks such as Dhrystone are now generally used to estimate computer performance in commonly used applications, and raw IPS has fallen into disuse.

The term is commonly used in association with a metric prefix (k, M, G, T, P, or E) to form kilo instructions per second (kIPS), mega instructions per second (MIPS), giga instructions per second (GIPS) and so on. Formerly TIPS was used occasionally for "thousand IPS".

A write buffer is a type of data buffer that can be used to hold data being written from the cache to main memory or to the next cache in the memory hierarchy to improve performance and reduce latency. It is used in certain CPU cache architectures like Intel's x86 and AMD64. In multi-core systems, write buffers destroy sequential consistency. Some software disciplines, like C11's data-race-freedom, are sufficient to regain a sequentially consistent view of memory.

A variation of write-through caching is called buffered write-through.