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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.)
Another reason for the disparity is the enormous increase in the size of memory since the start of the PC revolution in the 1980s. Originally, PCs contained less than 1 mebibyte of RAM, which often had a response time of 1 CPU clock cycle, meaning that it required 0 wait states.
Consequently, the proportion of die allocated to the memory array itself has decreased over time: from 70–78% for SDRAM and DDR1 to 47% for DDR2, 38% for DDR3, and potentially less than 30% for DDR4. [46] The specification defined standards for ×4, ×8 and ×16 memory devices with capacities of 2, 4, 8 and 16 Gbit. [1] [47]
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: Processor registers – the fastest possible access (usually 1 CPU cycle). A few ...
RAM with an access time of 70 ns will output valid data within 70 ns from the time that the address lines are valid. Some SRAM cells have a page mode, where words of a page (256, 512, or 1024 words) can be read sequentially with a significantly shorter access time (typically approximately 30 ns). The page is selected by setting the upper ...
The individual chips making up a 1 GB memory module are usually organized as 2 26 8-bit words, commonly expressed as 64M×8. Memory manufactured in this way is low-density RAM and is usually compatible with any motherboard specifying PC3200 DDR-400 memory. [18] [citation needed]
Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal–oxide–semiconductor (MOS) technology. While most DRAM memory cell designs use a capacitor and transistor ...
Additionally, a memory management unit (MMU) is a small device between CPU and RAM recalculating the actual memory address, for example to provide an abstraction of virtual memory or other tasks. As the RAM types used for primary storage are volatile (uninitialized at start up), a computer containing only such storage would not have a source to ...