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Secondary storage is non-volatile (retaining data when its power is shut off). Modern computer systems typically have two orders of magnitude more secondary storage than primary storage because secondary storage is less expensive. In modern computers, hard disk drives (HDDs) or solid-state drives (SSDs) are usually used as secondary storage.
Historical lowest retail price of computer memory and storage Electromechanical memory used in the IBM 602, an early punch multiplying calculator Detail of the back of a section of ENIAC, showing vacuum tubes Williams tube used as memory in the IAS computer c. 1951 8 GB microSDHC card on top of 8 bytes of magnetic-core memory (1 core is 1 bit.)
In operating systems, memory management is the function responsible for managing the computer's primary memory. [1]: 105–208 The memory management function keeps track of the status of each memory location, either allocated or free. It determines how memory is allocated among competing processes, deciding which gets memory, when they receive ...
Memory hierarchy of an AMD Bulldozer server. The number of levels in the memory hierarchy and the performance at each level has increased over time. The type of memory or storage components also change historically. [6] For example, the memory hierarchy of an Intel Haswell Mobile [7] processor circa 2013 is:
For simplicity, main memory is called "RAM" (an acronym of random-access memory) and secondary storage is called "disk" (a shorthand for hard disk drive, drum memory or solid-state drive, etc.), but as with many aspects of computing, the concepts are independent of the technology used.
The memory cell is the fundamental building block of computer memory. The memory cell is an electronic circuit that stores one bit of binary information and it must be set to store a logic 1 (high voltage level) and reset to store a logic 0 (low voltage level). Its value is maintained/stored until it is changed by the set/reset process.
The memory cells are laid out in rectangular arrays on the surface of the chip. The 1-bit memory cells are grouped in small units called words which are accessed together as a single memory address. Memory is manufactured in word length that is usually a power of two, typically N=1, 2, 4 or 8 bits.
Memory architecture also explains how binary digits are converted into electric signals and then stored in the memory cells. And also the structure of a memory cell. For example, dynamic memory is commonly used for primary data storage due to its fast access speed.