|Computer memory types|
|Early stage NVRAM|
Random-access memory (RAM // ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the same amount of time irrespective of the physical location of data inside the memory. In contrast, with other direct-access data storage media such as hard disks, CD-RWs, DVD-RWs and the older magnetic tapes and drum memory, the time required to read and write data items varies significantly depending on their physical locations on the recording medium, due to mechanical limitations such as media rotation speeds and arm movement.
RAM contains multiplexing and demultiplexing circuitry, to connect the data lines to the addressed storage for reading or writing the entry. Usually more than one bit of storage is accessed by the same address, and RAM devices often have multiple data lines and are said to be "8-bit" or "16-bit", etc. devices.
In today's technology, random-access memory takes the form of integrated circuit (IC) chips with MOS (metal-oxide-semiconductor) memory cells. RAM is normally associated with volatile types of memory (such as dynamic random-access memory (DRAM) modules), where stored information is lost if power is removed, although non-volatile RAM has also been developed.Other types of non-volatile memories exist that allow random access for read operations, but either do not allow write operations or have other kinds of limitations on them. These include most types of ROM and a type of flash memory called NOR-Flash .
The two main types of volatile random-access semiconductor memory are static random-access memory (SRAM) and dynamic random-access memory (DRAM). Commercial uses of semiconductor RAM date back to 1965, when IBM introduced the SP95 SRAM chip for their System/360 Model 95 computer, and Toshiba used DRAM memory cells for its Toscal BC-1411 electronic calculator, both based on bipolar transistors. Commercial MOS memory, based on MOS transistors, was developed in the late 1960s, and has since been the basis for all commercial semiconductor memory. The first commercial DRAM IC chip, the Intel 1103, was introduced in October 1970. Synchronous dynamic random-access memory (SDRAM) later debuted with the Samsung KM48SL2000 chip in 1992.
Early computers used relays, mechanical countersor delay lines for main memory functions. Ultrasonic delay lines were serial devices which could only reproduce data in the order it was written. Drum memory could be expanded at relatively low cost but efficient retrieval of memory items required knowledge of the physical layout of the drum to optimize speed. Latches built out of vacuum tube triodes, and later, out of discrete transistors, were used for smaller and faster memories such as registers. Such registers were relatively large and too costly to use for large amounts of data; generally only a few dozen or few hundred bits of such memory could be provided.
The first practical form of random-access memory was the Williams tube starting in 1947. It stored data as electrically charged spots on the face of a cathode ray tube. Since the electron beam of the CRT could read and write the spots on the tube in any order, memory was random access. The capacity of the Williams tube was a few hundred to around a thousand bits, but it was much smaller, faster, and more power-efficient than using individual vacuum tube latches. Developed at the University of Manchester in England, the Williams tube provided the medium on which the first electronically stored program was implemented in the Manchester Baby computer, which first successfully ran a program on 21 June 1948.In fact, rather than the Williams tube memory being designed for the Baby, the Baby was a testbed to demonstrate the reliability of the memory.
Magnetic-core memory was invented in 1947 and developed up until the mid-1970s. It became a widespread form of random-access memory, relying on an array of magnetized rings. By changing the sense of each ring's magnetization, data could be stored with one bit stored per ring. Since every ring had a combination of address wires to select and read or write it, access to any memory location in any sequence was possible. Magnetic core memory was the standard form of computer memory system until displaced by solid-state MOS (metal-oxide-silicon) semiconductor memory in integrated circuits (ICs) during the early 1970s.
Prior to the development of integrated read-only memory (ROM) circuits, permanent (or read-only) random-access memory was often constructed using diode matrices driven by address decoders, or specially wound core rope memory planes. [ citation needed ]
Semiconductor memory began in the 1960s with bipolar memory, which used bipolar transistors. While it improved performance, it could not compete with the lower price of magnetic core memory.
The invention of the MOSFET (metal-oxide-semiconductor field-effect transistor), also known as the MOS transistor, by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959,led to the development of metal-oxide-semiconductor (MOS) memory by John Schmidt at Fairchild Semiconductor in 1964. In addition to higher performance, MOS semiconductor memory was cheaper and consumed less power than magnetic core memory. The development of silicon-gate MOS integrated circuit (MOS IC) technology by Federico Faggin at Fairchild in 1968 enabled the production of MOS memory chips. MOS memory overtook magnetic core memory as the dominant memory technology in the early 1970s.
An integrated bipolar static random-access memory (SRAM) was invented by Robert H. Norman at Fairchild Semiconductor in 1963.It was followed by the development of MOS SRAM by John Schmidt at Fairchild in 1964. SRAM became an alternative to magnetic-core memory, but required six MOS transistors for each bit of data. Commercial use of SRAM began in 1965, when IBM introduced the SP95 memory chip for the System/360 Model 95.
Dynamic random-access memory (DRAM) allowed replacement of a 4 or 6-transistor latch circuit by a single transistor for each memory bit, greatly increasing memory density at the cost of volatility. Data was stored in the tiny capacitance of each transistor, and had to be periodically refreshed every few milliseconds before the charge could leak away. Toshiba's Toscal BC-1411 electronic calculator, which was introduced in 1965,used a form of capacitive bipolar DRAM, storing 180-bit data on discrete memory cells, consisting of germanium bipolar transistors and capacitors. While it offered improved performance over magnetic-core memory, bipolar DRAM could not compete with the lower price of the then dominant magnetic-core memory.
MOS technology is the basis for modern DRAM. In 1966, Dr. Robert H. Dennard at the IBM Thomas J. Watson Research Center was working on MOS memory. While examining the characteristics of MOS technology, he found it was capable of building capacitors, and that storing a charge or no charge on the MOS capacitor could represent the 1 and 0 of a bit, while the MOS transistor could control writing the charge to the capacitor. This led to his development of a single-transistor DRAM memory cell. µm MOS process with a capacity of 1 Kibit, and was released in 1970.In 1967, Dennard filed a patent under IBM for a single-transistor DRAM memory cell, based on MOS technology. The first commercial DRAM IC chip was the Intel 1103, which was manufactured on an 8
Synchronous dynamic random-access memory (SDRAM) was developed by Samsung Electronics. The first commercial SDRAM chip was the Samsung KM48SL2000, which had a capacity of 16 Mibit. It was introduced by Samsung in 1992, and mass-produced in 1993. The first commercial DDR SDRAM (double data rate SDRAM) memory chip was Samsung's 64 Mibit DDR SDRAM chip, released in June 1998. GDDR (graphics DDR) is a form of DDR SGRAM (synchronous graphics RAM), which was first released by Samsung as a 16 Mibit memory chip in 1998.
The two widely used forms of modern RAM are static RAM (SRAM) and dynamic RAM (DRAM). In SRAM, a bit of data is stored using the state of a six-transistor memory cell, typically using six MOSFETs (metal-oxide-semiconductor field-effect transistors). This form of RAM is more expensive to produce, but is generally faster and requires less dynamic power than DRAM. In modern computers, SRAM is often used as cache memory for the CPU. DRAM stores a bit of data using a transistor and capacitor pair (typically a MOSFET and MOS capacitor, respectively),which together comprise a DRAM cell. The capacitor holds a high or low charge (1 or 0, respectively), and the transistor acts as a switch that lets the control circuitry on the chip read the capacitor's state of charge or change it. As this form of memory is less expensive to produce than static RAM, it is the predominant form of computer memory used in modern computers.
Both static and dynamic RAM are considered volatile, as their state is lost or reset when power is removed from the system. By contrast, read-only memory (ROM) stores data by permanently enabling or disabling selected transistors, such that the memory cannot be altered. Writeable variants of ROM (such as EEPROM and flash memory) share properties of both ROM and RAM, enabling data to persist without power and to be updated without requiring special equipment. These persistent forms of semiconductor ROM include USB flash drives, memory cards for cameras and portable devices, and solid-state drives. ECC memory (which can be either SRAM or DRAM) includes special circuitry to detect and/or correct random faults (memory errors) in the stored data, using parity bits or error correction codes.
In general, the term RAM refers solely to solid-state memory devices (either DRAM or SRAM), and more specifically the main memory in most computers. In optical storage, the term DVD-RAM is somewhat of a misnomer since, unlike CD-RW or DVD-RW it does not need to be erased before reuse. Nevertheless, a DVD-RAM behaves much like a hard disc drive if somewhat slower.
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 value in the memory cell can be accessed by reading it.
In SRAM, the memory cell is a type of flip-flop circuit, usually implemented using FETs. This means that SRAM requires very low power when not being accessed, but it is expensive and has low storage density.
A second type, DRAM, is based around a capacitor. Charging and discharging this capacitor can store a "1" or a "0" in the cell. However, the charge in this capacitor slowly leaks away, and must be refreshed periodically. Because of this refresh process, DRAM uses more power, but it can achieve greater storage densities and lower unit costs compared to SRAM.
To be useful, memory cells must be readable and writeable. Within the RAM device, multiplexing and demultiplexing circuitry is used to select memory cells. Typically, a RAM device has a set of address lines A0... An, and for each combination of bits that may be applied to these lines, a set of memory cells are activated. Due to this addressing, RAM devices virtually always have a memory capacity that is a power of two.
Usually several memory cells share the same address. For example, a 4 bit 'wide' RAM chip has 4 memory cells for each address. Often the width of the memory and that of the microprocessor are different, for a 32 bit microprocessor, eight 4 bit RAM chips would be needed.
Often more addresses are needed than can be provided by a device. In that case, external multiplexors to the device are used to activate the correct device that is being accessed.
One can read and over-write data in RAM. Many computer systems have a memory hierarchy consisting of processor registers, on-die SRAM caches, external caches, DRAM, paging systems and virtual memory or swap space on a hard drive. This entire pool of memory may be referred to as "RAM" by many developers, even though the various subsystems can have very different access times, violating the original concept behind the random access term in RAM. Even within a hierarchy level such as DRAM, the specific row, column, bank, rank, channel, or interleave organization of the components make the access time variable, although not to the extent that access time to rotating storage media or a tape is variable. The overall goal of using a memory hierarchy is to obtain the highest possible average access performance while minimizing the total cost of the entire memory system (generally, the memory hierarchy follows the access time with the fast CPU registers at the top and the slow hard drive at the bottom).
In many modern personal computers, the RAM comes in an easily upgraded form of modules called memory modules or DRAM modules about the size of a few sticks of chewing gum. These can quickly be replaced should they become damaged or when changing needs demand more storage capacity. As suggested above, smaller amounts of RAM (mostly SRAM) are also integrated in the CPU and other ICs on the motherboard, as well as in hard-drives, CD-ROMs, and several other parts of the computer system.
In addition to serving as temporary storage and working space for the operating system and applications, RAM is used in numerous other ways.
Most modern operating systems employ a method of extending RAM capacity, known as "virtual memory". A portion of the computer's hard drive is set aside for a paging file or a scratch partition, and the combination of physical RAM and the paging file form the system's total memory. (For example, if a computer has 2 GB (1024^3 B) of RAM and a 1 GB page file, the operating system has 3 GB total memory available to it.) When the system runs low on physical memory, it can "swap" portions of RAM to the paging file to make room for new data, as well as to read previously swapped information back into RAM. Excessive use of this mechanism results in thrashing and generally hampers overall system performance, mainly because hard drives are far slower than RAM.
Software can "partition" a portion of a computer's RAM, allowing it to act as a much faster hard drive that is called a RAM disk. A RAM disk loses the stored data when the computer is shut down, unless memory is arranged to have a standby battery source.
Sometimes, the contents of a relatively slow ROM chip are copied to read/write memory to allow for shorter access times. The ROM chip is then disabled while the initialized memory locations are switched in on the same block of addresses (often write-protected). This process, sometimes called shadowing, is fairly common in both computers and embedded systems.
As a common example, the BIOS in typical personal computers often has an option called “use shadow BIOS” or similar. When enabled, functions that rely on data from the BIOS's ROM instead use DRAM locations (most can also toggle shadowing of video card ROM or other ROM sections). Depending on the system, this may not result in increased performance, and may cause incompatibilities. For example, some hardware may be inaccessible to the operating system if shadow RAM is used. On some systems the benefit may be hypothetical because the BIOS is not used after booting in favor of direct hardware access. Free memory is reduced by the size of the shadowed ROMs.
Several new types of non-volatile RAM, which preserve data while powered down, are under development. The technologies used include carbon nanotubes and approaches utilizing Tunnel magnetoresistance. Amongst the 1st generation MRAM, a 128 KiB (128 × 210 bytes) chip was manufactured with 0.18 µm technology in the summer of 2003.[ citation needed ] In June 2004, Infineon Technologies unveiled a 16 MiB (16 × 220 bytes) prototype again based on 0.18 µm technology. There are two 2nd generation techniques currently in development: thermal-assisted switching (TAS) which is being developed by Crocus Technology, and spin-transfer torque (STT) on which Crocus, Hynix, IBM, and several other companies are working. Nantero built a functioning carbon nanotube memory prototype 10 GiB (10 × 230 bytes) array in 2004. Whether some of these technologies can eventually take significant market share from either DRAM, SRAM, or flash-memory technology, however, remains to be seen.
Since 2006, "solid-state drives" (based on flash memory) with capacities exceeding 256 gigabytes and performance far exceeding traditional disks have become available. This development has started to blur the definition between traditional random-access memory and "disks", dramatically reducing the difference in performance.
Some kinds of random-access memory, such as "EcoRAM", are specifically designed for server farms, where low power consumption is more important than speed.
The "memory wall" is the growing disparity of speed between CPU and memory outside the CPU chip. An important reason for this disparity is the limited communication bandwidth beyond chip boundaries, which is also referred to as bandwidth wall. From 1986 to 2000, CPU speed improved at an annual rate of 55% while memory speed only improved at 10%. Given these trends, it was expected that memory latency would become an overwhelming bottleneck in computer performance.
CPU speed improvements slowed significantly partly due to major physical barriers and partly because current CPU designs have already hit the memory wall in some sense. Intel summarized these causes in a 2005 document.
First of all, as chip geometries shrink and clock frequencies rise, the transistor leakage current increases, leading to excess power consumption and heat... Secondly, the advantages of higher clock speeds are in part negated by memory latency, since memory access times have not been able to keep pace with increasing clock frequencies. Third, for certain applications, traditional serial architectures are becoming less efficient as processors get faster (due to the so-called Von Neumann bottleneck), further undercutting any gains that frequency increases might otherwise buy. In addition, partly due to limitations in the means of producing inductance within solid state devices, resistance-capacitance (RC) delays in signal transmission are growing as feature sizes shrink, imposing an additional bottleneck that frequency increases don't address.
The RC delays in signal transmission were also noted in "Clock Rate versus IPC: The End of the Road for Conventional Microarchitectures"which projected a maximum of 12.5% average annual CPU performance improvement between 2000 and 2014.
A different concept is the processor-memory performance gap, which can be addressed by 3D integrated circuits that reduce the distance between the logic and memory aspects that are further apart in a 2D chip.Memory subsystem design requires a focus on the gap, which is widening over time. The main method of bridging the gap is the use of caches; small amounts of high-speed memory that houses recent operations and instructions nearby the processor, speeding up the execution of those operations or instructions in cases where they are called upon frequently. Multiple levels of caching have been developed to deal with the widening gap, and the performance of high-speed modern computers relies on evolving caching techniques. There can be up to a 53% difference between the growth in speed of processor speeds and the lagging speed of main memory access.
Solid-state hard drives have continued to increase in speed, from ~400 Mbit/s via SATA3 in 2012 up to ~3 GB/s via NVMe/PCIe in 2018, closing the gap between RAM and hard disk speeds, although RAM continues to be an order of magnitude faster, with single-lane DDR4 3200 capable of 25 GB/s, and modern GDDR even faster. Fast, cheap, non-volatile solid state drives have replaced some functions formerly performed by RAM, such as holding certain data for immediate availability in server farms - 1 Terabyte of SSD storage can be had for $200, while 1TB of RAM would cost thousands of dollars.
|Date of introduction||Chip name||Capacity (bits)||Access time||SRAM type||Manufacturer(s)||Process||MOSFET||Ref|
|March 1963||N/A||1-bit||?||Bipolar (cell)||Fairchild||N/A||N/A|
|1101||256-bit||850 ns||MOSFET||Intel||12,000 nm||PMOS|
|1974||5101||1 Kibit||800 ns||MOSFET||Intel||?||CMOS|
|2102A||1 Kibit||350 ns||MOSFET||Intel||?||NMOS (depletion)|
|1975||2114||4 Kibit||450 ns||MOSFET||Intel||?||NMOS|
|1976||2115||1 Kibit||70 ns||MOSFET||Intel||?||NMOS (HMOS)|
|2147||4 Kibit||55 ns||MOSFET||Intel||?||NMOS (HMOS)|
|1978||HM6147||4 Kibit||55 ns||MOSFET||Hitachi||3,000 nm||CMOS (twin-well)|
|TMS4016||16 Kibit||?||MOSFET||Texas Instruments||?||NMOS|
|1980||?||16 Kibit||?||MOSFET||Hitachi, Toshiba||?||CMOS|
|1981||?||16 Kibit||?||MOSFET||Texas Instruments||2,500 nm||NMOS|
|October 1981||?||4 Kibit||18 ns||MOSFET||Matsushita, Toshiba||2,000 nm||CMOS|
|1982||?||64 Kibit||?||MOSFET||Intel||1,500 nm||NMOS (HMOS)|
|February 1983||?||64 Kibit||50 ns||MOSFET||Mitsubishi||?||CMOS|
|1984||?||256 Kibit||?||MOSFET||Toshiba||1,200 nm||CMOS|
|1987||?||1 Mibit||?||MOSFET||Sony, Hitachi, Mitsubishi, Toshiba||?||CMOS|
|December 1987||?||256 Kibit||10 ns||BiMOS||Texas Instruments||800 nm||BiCMOS|
|1990||?||4 Mibit||15–23 ns||MOSFET||NEC, Toshiba, Hitachi, Mitsubishi||?||CMOS|
|1992||?||16 Mibit||12–15 ns||MOSFET||Fujitsu, NEC||400 nm|
|December 1994||?||512 Kibit||2.5 ns||MOSFET||IBM||?||CMOS (SOI)|
|1995||?||4 Mibit||6 ns||Cache (SyncBurst)||Hitachi||100 nm||CMOS|
|Date of introduction||Chip name||Capacity (bits)||DRAM type||Manufacturer(s)||Process||MOSFET||Area||Ref|
|1970||1102||1 Kibit||DRAM (IC)||Intel, Honeywell||?||PMOS||?|
|1103||1 Kibit||DRAM||Intel||8,000 nm||PMOS||10 mm²|
|?||2 Kibit||DRAM||General Instrument||?||PMOS||13 mm²|
|1973||?||8 Kibit||DRAM||IBM||?||PMOS||19 mm²|
|1977||?||64 Kibit||DRAM||NTT||?||NMOS||35 mm²|
|?||64 Kibit||DRAM||Siemens||?||VMOS||25 mm²|
|1980||?||256 Kibit||DRAM||NEC, NTT||1,000– 1,500 nm||NMOS||34–42 mm²|
|1981||?||288 Kibit||DRAM||IBM||?||MOS||25 mm²|
|1983||?||64 Kibit||DRAM||Intel||1,500 nm||CMOS||20 mm²|
|256 Kibit||DRAM||NTT||?||CMOS||31 mm²|
|January 5, 1984||?||8 Mibit||DRAM||Hitachi||?||MOS||?|
|February 1984||?||1 Mibit||DRAM||Hitachi, NEC||1,000 nm||NMOS||74–76 mm²|
|NTT||800 nm||CMOS||53 mm²|
|1984||TMS4161||64 Kibit||DPRAM (VRAM)||Texas Instruments||?||NMOS||?|
|January 1985||μPD41264||258 Kibit||DPRAM (VRAM)||NEC||?||NMOS||?|
|June 1986||?||1 Mibit||PSRAM||Toshiba||?||CMOS||?|
|1986||?||4 Mibit||DRAM||NEC||800 nm||NMOS||99 mm²|
|Texas Instruments, Toshiba||1,000 nm||CMOS||100–137 mm²|
|1987||?||16 Mibit||DRAM||NTT||700 nm||CMOS||148 mm²|
|October 1988||?||512 Kibit||HSDRAM||IBM||1,000 nm||CMOS||78 mm²|
|1991||?||64 Mibit||DRAM||Matsushita, Mitsubishi, Fujitsu, Toshiba||400 nm||CMOS||?|
|1993||?||256 Mibit||DRAM||Hitachi, NEC||250 nm||CMOS||?|
|1995||?||4 Mibit||DPRAM (VRAM)||Hitachi||?||CMOS||?|
|January 9, 1995||?||1 Gibit||DRAM||NEC||250 nm||CMOS||?|
|1997||?||4 Gb||QLC||NEC||150 nm||CMOS||?|
|June 2001||TC51W3216XB||32 Mibit||PSRAM||Toshiba||?||CMOS||?|
|February 2001||?||4 Gibit||DRAM||Samsung||100 nm||CMOS||?|
|Date of introduction||Chip name||Capacity (bits)||SDRAM type||Manufacturer(s)||Process||MOSFET||Area||Ref|
|1996||MSM5718C50||18 Mb||RDRAM||Oki||?||CMOS||325 mm²|
|N64 RDRAM||36 Mb||RDRAM||NEC||?||CMOS||?|
|?||1 Gb||SDR||Mitsubishi||150 nm||CMOS||?|
|1998||MD5764802||64 Mb||RDRAM||Oki||?||CMOS||325 mm²|
|March 1998||Direct RDRAM||72 Mb||RDRAM||Rambus||?||CMOS||?|
|June 1998||?||64 Mb||DDR||Samsung||?||CMOS||?|
|1 Gb||DDR||Samsung||140 nm||CMOS||?|
|2000||GS eDRAM||32 Mb||eDRAM||Sony, Toshiba||180 nm||CMOS||279 mm²|
|2003||EE+GS eDRAM||32 Mb||eDRAM||Sony, Toshiba||90 nm||CMOS||86 mm²|
|?||72 Mb||DDR3||Samsung||90 nm||CMOS||?|
|2004||?||2 Gb||DDR2||Samsung||80 nm||CMOS||?|
|2005||EE+GS eDRAM||32 Mb||eDRAM||Sony, Toshiba||65 nm||CMOS||86 mm²|
|Xenos eDRAM||80 Mb||eDRAM||NEC||90 nm||CMOS||?|
|?||512 Mb||DDR3||Samsung||80 nm||CMOS||?|
|2006||?||1 Gb||DDR2||Hynix||60 nm||CMOS||?|
|April 2008||?||8 Gb||DDR3||Samsung||50 nm||CMOS||?|
|2008||?||16 Gb||DDR3||Samsung||50 nm||CMOS||?|
|2 Gb||DDR3||Hynix||40 nm|
|2011||?||16 Gb||DDR3||Hynix||40 nm||CMOS||?|
|2 Gb||DDR4||Hynix||30 nm||CMOS||?|
|2014||?||8 Gb||LPDDR4||Samsung||20 nm||CMOS||?|
|2015||?||12 Gb||LPDDR4||Samsung||20 nm||CMOS||?|
|2018||?||8 Gb||LPDDR5||Samsung||10 nm||FinFET||?|
|128 Gb||DDR4||Samsung||10 nm||FinFET||?|
|Date of introduction||Chip name||Capacity (bits)||SDRAM type||Manufacturer(s)||Process||MOSFET||Area||Ref|
|November 1994||HM5283206||8 Mibit||SGRAM (SDR)||Hitachi||350 nm||CMOS||58 mm²|
|December 1994||µPD481850||8 Mibit||SGRAM (SDR)||NEC||?||CMOS||280 mm²|
|1997||µPD4811650||16 Mibit||SGRAM (SDR)||NEC||350 nm||CMOS||280 mm²|
|September 1998||?||16 Mibit||SGRAM (GDDR)||Samsung||?||CMOS||?|
|1999||KM4132G112||32 Mibit||SGRAM (SDR)||Samsung||?||CMOS||?|
|2002||?||128 Mibit||SGRAM (GDDR2)||Samsung||?||CMOS||?|
|2003||?||256 Mibit||SGRAM (GDDR2)||Samsung||?||CMOS||?|
|March 2005||K4D553238F||256 Mibit||SGRAM (GDDR)||Samsung||?||CMOS||77 mm²|
|October 2005||?||256 Mibit||SGRAM (GDDR4)||Samsung||?||CMOS||?|
|2005||?||512 Mibit||SGRAM (GDDR4)||Hynix||?||CMOS||?|
|2007||?||1 Gibit||SGRAM (GDDR5)||Hynix||60 nm|
|2009||?||2 Gibit||SGRAM (GDDR5)||Hynix||40 nm|
|2010||K4W1G1646G||1 Gibit||SGRAM (GDDR3)||Samsung||?||CMOS||100 mm²|
|2012||?||4 Gibit||SGRAM (GDDR3)||SK Hynix||?||CMOS||?|
|March 2016||MT58K256M32JA||8 Gibit||SGRAM (GDDR5X)||Micron||20 nm||CMOS||140 mm²|
|June 2016||?||32 Gibit||HBM2||Samsung||20 nm||CMOS||?|
|2017||?||64 Gibit||HBM2||Samsung||20 nm||CMOS||?|
|January 2018||K4ZAF325BM||16 Gibit||SGRAM (GDDR6)||Samsung||10 nm||FinFET||?|
In computing, memory refers to a device that is used to store information for immediate use in a computer or related computer hardware device. It typically refers to semiconductor memory, specifically metal–oxide–semiconductor (MOS) memory, where data is stored within MOS memory cells on a silicon integrated circuit chip. The term "memory" is often synonymous with the term "primary storage". Computer memory operates at a high speed, for example random-access memory (RAM), as a distinction from storage that provides slow-to-access information but offers higher capacities. If needed, contents of the computer memory can be transferred to secondary storage; a very common way of doing this is through a memory management technique called "virtual memory". An archaic synonym for memory is store.
Double Data Rate Synchronous Dynamic Random-Access Memory, officially abbreviated as DDR SDRAM, is a double data rate (DDR) synchronous dynamic random-access memory (SDRAM) class of memory integrated circuits used in computers. DDR SDRAM, also retroactively called DDR1 SDRAM, has been superseded by DDR2 SDRAM, DDR3 SDRAM and DDR4 SDRAM. None of its successors are forward or backward compatible with DDR1 SDRAM, meaning DDR2, DDR3, and DDR4 memory modules will not work in DDR1-equipped motherboards, and vice versa.
Flash memory is an electronic (solid-state) non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory are named after the NAND and NOR logic gates. The individual flash memory cells, consisting of floating-gate MOSFETs, exhibit internal characteristics similar to those of the corresponding gates.
Static random-access memory is a type of semiconductor random-access memory (RAM) that uses bistable latching circuitry (flip-flop) to store each bit. SRAM exhibits data remanence, but it is still volatile in the conventional sense that data is eventually lost when the memory is not powered.
Dynamic random-access memory (DRAM) is a type of random access semiconductor memory that stores each bit of data in a memory cell consisting of a tiny capacitor and a transistor, both typically based on metal-oxide-semiconductor (MOS) technology. The capacitor can either be charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1. The electric charge on the capacitors slowly leaks off, so without intervention the data on the chip would soon be lost. To prevent this, DRAM requires an external memory refresh circuit which periodically rewrites the data in the capacitors, restoring them to their original charge. This refresh process is the defining characteristic of dynamic random-access memory, in contrast to static random-access memory (SRAM) which does not require data to be refreshed. Unlike flash memory, DRAM is volatile memory, since it loses its data quickly when power is removed. However, DRAM does exhibit limited data remanence.
Synchronous dynamic random-access memory (SDRAM) is any dynamic random-access memory (DRAM) where the operation of its external pin interface is coordinated by an externally supplied clock signal.
Non-volatile random-access memory (NVRAM) is random-access memory that is non-volatile. This is in contrast to dynamic random-access memory (DRAM) and static random-access memory (SRAM), which both maintain data only for as long as power is applied.
Volatile memory, in contrast to non-volatile memory, is computer memory that requires power to maintain the stored information; it retains its contents while powered on but when the power is interrupted, the stored data is quickly lost.
Semiconductor memory is a digital electronic semiconductor device used for digital data storage, such as computer memory. It typically refers to MOS memory, where data is stored within metal–oxide–semiconductor (MOS) memory cells on a silicon integrated circuit memory chip. There are numerous different types using different semiconductor technologies. The two main types of random-access memory (RAM) are static RAM (SRAM), which uses several transistors per memory cell, and dynamic RAM (DRAM), which uses a single transistor and MOS capacitor per cell. Non-volatile memory uses floating-gate memory cells, which consist of a single transistor per cell.
Ferroelectric RAM is a random-access memory similar in construction to DRAM but using a ferroelectric layer instead of a dielectric layer to achieve non-volatility. FeRAM is one of a growing number of alternative non-volatile random-access memory technologies that offer the same functionality as flash memory.
Memory refresh is the process of periodically reading information from an area of computer memory and immediately rewriting the read information to the same area without modification, for the purpose of preserving the information. Memory refresh is a background maintenance process required during the operation of semiconductor dynamic random-access memory (DRAM), the most widely used type of computer memory, and in fact is the defining characteristic of this class of memory.
The 32 nm node is the step following the 45 nm process process in CMOS (MOSFET) semiconductor device fabrication. "32-nanometre" refers to the average half-pitch of a memory cell at this technology level. Toshiba produced commercial 32 GiB NAND flash memory chips with the 32 nm process in 2009. Intel and AMD produced commercial microchips using the 32-nanometre process in the early 2010s. IBM and the Common Platform also developed a 32 nm high-κ metal gate process. Intel began selling its first 32 nm processors using the Westmere architecture on 7 January 2010.
GDDR4 SGRAM, an abbreviation for double data rate type four synchronous graphics random access memory, is a type of graphics card memory specified by the JEDEC Semiconductor Memory Standard. It is a rival medium to Rambus's XDR DRAM. GDDR4 is based on DDR3 SDRAM technology and was intended to replace the DDR2-based GDDR3, but it ended up being replaced by GDDR5 within a year.
The transistor count is the number of transistors on an integrated circuit (IC). It typically refers to the number of MOSFETs on an IC chip, as all modern ICs use MOSFETs. It is the most common measure of IC complexity. The rate at which MOS transistor counts have increased generally follows Moore's law, which observed that the transistor count doubles approximately every two years.
The memory controller is a digital circuit that manages the flow of data going to and from the computer's main memory. A memory controller can be a separate chip or integrated into another chip, such as being placed on the same die or as an integral part of a microprocessor; in the latter case, it is usually called an integrated memory controller (IMC). A memory controller is sometimes also called a memory chip controller (MCC) or a memory controller unit (MCU).
GDDR5, an abbreviation for graphics double data rate type five synchronous dynamic random-access memory, is a modern type of synchronous graphics random-access memory (SGRAM) with a high bandwidth interface designed for use in graphics cards, game consoles, and high-performance computing. It is a type of GDDR SDRAM.
Double Data Rate 4 Synchronous Dynamic Random-Access Memory, officially abbreviated as DDR4 SDRAM, is a type of synchronous dynamic random-access memory with a high bandwidth interface.
Thyristor RAM (T-RAM) is a new (2009) type of random-access memory invented and developed by T-RAM Semiconductor, which departs from the usual designs of memory cells, combining the strengths of the DRAM and SRAM: high density and high speed. This technology, which exploits the electrical property known as negative differential resistance and is called thin capacitively-coupled thyristor, is used to create memory cells capable of very high packing densities. Due to this, the memory is highly scalable, and already has a storage density that is several times higher than found in conventional six-transistor SRAM memory. It was expected that the next generation of T-RAM memory will have the same density as DRAM.
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 and reset to store a logic 0. Its value is maintained/stored until it is changed by the set/reset process. The value in the memory cell can be accessed by reading it.
The i1103 was manufactured on a 6-mask silicon-gate P-MOS process with 8 μm minimum features. The resulting product had a 2,400 µm² memory cell size, a die size just under 10 mm², and sold for around $21.
The first commercial synchronous DRAM, the Samsung 16-Mbit KM48SL2000, employs a single-bank architecture that lets system designers easily transition from asynchronous to synchronous systems.
The announcement of 1M DRAM in 1984 began the era of megabytes.