Random-access memory

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Example of writable volatile random-access memory: Synchronous Dynamic RAM modules, primarily used as main memory in personal computers, workstations, and servers. Swissbit 2GB PC2-5300U-555.jpg
Example of writable volatile random-access memory: Synchronous Dynamic RAM modules, primarily used as main memory in personal computers, workstations, and servers.
8GB DDR3 RAM stick with a white heatsink Random Access Memory HyperX.jpg
8GB DDR3 RAM stick with a white heatsink

Random-access memory (RAM; /ræm/ ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. [1] [2] 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), where 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.[ clarification needed ]

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. [3] 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.


These IBM tabulating machines from the mid-1930s used mechanical counters to store information Early SSA accounting operations.jpg
These IBM tabulating machines from the mid-1930s used mechanical counters to store information
1 Megabit (MBit) chip, one of the last models developed by VEB Carl Zeiss Jena in 1989 Bundesarchiv Bild 183-1989-0406-022, VEB Carl Zeiss Jena, 1-Megabit-Chip.jpg
1 Megabit (MBit) chip, one of the last models developed by VEB Carl Zeiss Jena in 1989

Early computers used relays, mechanical counters [4] or 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. [5] 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. [6] [7]

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. [8]

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. [9]


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, [10] led to the development of metal-oxide-semiconductor (MOS) memory by John Schmidt at Fairchild Semiconductor in 1964. [8] [11] In addition to higher performance, MOS semiconductor memory was cheaper and consumed less power than magnetic core memory. [8] 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. [12] MOS memory overtook magnetic core memory as the dominant memory technology in the early 1970s. [8]

An integrated bipolar static random-access memory (SRAM) was invented by Robert H. Norman at Fairchild Semiconductor in 1963. [13] It was followed by the development of MOS SRAM by John Schmidt at Fairchild in 1964. [8] SRAM became an alternative to magnetic-core memory, but required six MOS transistors for each bit of data. [14] Commercial use of SRAM began in 1965, when IBM introduced the SP95 memory chip for the System/360 Model 95. [9]

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, [15] [16] [17] used a form of capacitive bipolar DRAM, storing 180-bit data on discrete memory cells, consisting of germanium bipolar transistors and capacitors. [16] [17] 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. [18]

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. [14] In 1967, Dennard filed a patent under IBM for a single-transistor DRAM memory cell, based on MOS technology. [19] The first commercial DRAM IC chip was the Intel 1103, which was manufactured on an 8 µm MOS process with a capacity of 1  kbit, and was released in 1970. [8] [20] [21]

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  Mbit. [22] It was introduced by Samsung in 1992, [23] and mass-produced in 1993. [22] The first commercial DDR SDRAM (double data rate SDRAM) memory chip was Samsung's 64 Mbit DDR SDRAM chip, released in June 1998. [24] GDDR (graphics DDR) is a form of DDR SGRAM (synchronous graphics RAM), which was first released by Samsung as a 16 Mbit memory chip in 1998. [25]


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), [26] 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.

Memory cell

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.

SRAM Cell (6 Transistors) SRAM Cell (6 Transistors).svg
SRAM Cell (6 Transistors)
DRAM Cell (1 Transistor and one capacitor) DRAM Cell Structure (Model of Single Circuit Cell).PNG
DRAM Cell (1 Transistor and one capacitor)


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.

Memory hierarchy

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.

Other uses of RAM

A SO-DIMM stick of laptop RAM, roughly half the size of desktop RAM. Samsung-1GB-DDR2-Laptop-RAM.jpg
A SO-DIMM stick of laptop RAM, roughly half the size of desktop RAM.

In addition to serving as temporary storage and working space for the operating system and applications, RAM is used in numerous other ways.

Virtual memory

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 (10243 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.

RAM disk

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, or changes to the RAM disk are written out to a nonvolatile disk. The RAM disk is reloaded from the physical disk upon RAM disk initialization.

Shadow RAM

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. [27]

Recent developments

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 kbit (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  MB (16 × 220 bytes) prototype again based on 0.18 µm technology. There are two 2nd generation techniques currently in development: thermal-assisted switching (TAS) [28] which is being developed by Crocus Technology, and spin-transfer torque (STT) on which Crocus, Hynix, IBM, and several other companies are working. [29] Nantero built a functioning carbon nanotube memory prototype 10  GB (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. [30]

Memory wall

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. [31]

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. [32]

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" [33] 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. [34] Memory subsystem design requires a focus on the gap, which is widening over time. [35] 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. [36] There can be up to a 53% difference between the growth in speed of processor and the lagging speed of main memory access. [37]

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 1 TB of RAM would cost thousands of dollars. [38] [39]



Static random-access memory (SRAM)
Date of introductionChip nameCapacity (bits) Access time SRAM typeManufacturer(s) Process MOSFET Ref
March 1963N/A 1-bit ? Bipolar (cell) Fairchild N/AN/A [9]
1965? 8-bit ? Bipolar IBM ?N/A
SP95 16-bit ?BipolarIBM?N/A [40]
? 64-bit ? MOSFET Fairchild? PMOS [41]
1966TMC316216-bit?Bipolar (TTL) Transitron ?N/A [8]
???MOSFET NEC ?? [42]
1968?64-bit?MOSFETFairchild?PMOS [42]
512-bit ?MOSFETIBM?NMOS [41]
1969? 128-bit ?BipolarIBM?N/A [9]
1101 256-bit 850 ns MOSFET Intel 12,000 nm PMOS [43] [44] [45] [46]
197221021 kbit ?MOSFETIntel?NMOS [43]
197451011 kbit800 nsMOSFETIntel? CMOS [43] [47]
2102A1 kbit350 nsMOSFETIntel?NMOS (depletion) [43] [48]
197521144 kbit450 nsMOSFETIntel?NMOS [43] [47]
197621151 kbit70 nsMOSFETIntel?NMOS (HMOS) [43] [44]
21474 kbit55 nsMOSFETIntel?NMOS (HMOS) [43] [49]
1977?4 kbit?MOSFET Toshiba ?CMOS [44]
1978HM61474 kbit55 nsMOSFET Hitachi 3,000 nm CMOS (twin-well) [49]
TMS401616 kbit?MOSFET Texas Instruments ?NMOS [44]
1980?16 kbit?MOSFETHitachi, Toshiba?CMOS [50]
64 kbit?MOSFET Matsushita
1981?16 kbit?MOSFETTexas Instruments2,500 nmNMOS [50]
October 1981?4 kbit18 nsMOSFETMatsushita, Toshiba2,000 nmCMOS [51]
1982?64 kbit?MOSFETIntel 1,500 nm NMOS (HMOS) [50]
February 1983?64 kbit50 nsMOSFET Mitsubishi ?CMOS [52]
1984?256 kbit?MOSFETToshiba1,200 nmCMOS [50] [45]
1987?1 Mbit ?MOSFET Sony, Hitachi, Mitsubishi, Toshiba?CMOS [50]
December 1987?256 kbit10 ns BiMOS Texas Instruments800 nm BiCMOS [53]
1990?4 Mbit1523 nsMOSFETNEC, Toshiba, Hitachi, Mitsubishi?CMOS [50]
1992?16 Mbit1215 nsMOSFET Fujitsu, NEC400 nm
December 1994?512 kbit2.5 nsMOSFETIBM?CMOS (SOI) [54]
1995?4 Mbit6 ns Cache (SyncBurst)Hitachi100 nmCMOS [55]
256 Mbit?MOSFET Hyundai ?CMOS [56]


Dynamic random-access memory (DRAM)
Date of introductionChip nameCapacity (bits)DRAM typeManufacturer(s) Process MOSFET AreaRef
1965N/A 1 bit DRAM (cell) Toshiba N/AN/AN/A [16] [17]
1967N/A1 bitDRAM (cell) IBM N/A MOS N/A [19] [42]
1968? 256 bit DRAM (IC) Fairchild ? PMOS ? [8]
1969N/A1 bitDRAM (cell) Intel N/APMOSN/A [42]
1970 1102 1 kbit DRAM (IC)Intel, Honeywell ?PMOS? [42]
1103 1 kbitDRAMIntel8,000 nm PMOS10 mm² [57] [58] [20]
1971μPD4031 kbitDRAM NEC ? NMOS ? [59]
?2 kbitDRAM General Instrument ?PMOS13 mm² [60]
197221074 kbitDRAMIntel?NMOS? [43] [61]
1973?8 kbitDRAMIBM?PMOS19 mm² [60]
1975211616 kbitDRAMIntel?NMOS? [62] [8]
1977?64 kbitDRAM NTT ?NMOS35 mm² [60]
1979MK481616 kbit PSRAM Mostek ?NMOS? [63]
?64 kbitDRAM Siemens ? VMOS 25 mm² [60]
1980?256 kbitDRAMNEC, NTT1,000 1,500 nm NMOS3442 mm² [60]
1981?288 kbitDRAMIBM?MOS25 mm² [64]
1983?64 kbitDRAMIntel 1,500 nm CMOS 20 mm² [60]
256 kbitDRAMNTT?CMOS31 mm²
January 5, 1984?8 Mbit DRAM Hitachi ?MOS? [65] [66]
February 1984?1 MbitDRAMHitachi, NEC 1,000 nm NMOS7476 mm² [60] [67]
NTT 800 nm CMOS53 mm² [60] [67]
1984TMS416164 kbit DPRAM (VRAM) Texas Instruments ?NMOS? [68] [69]
January 1985μPD41264256 kbitDPRAM (VRAM)NEC?NMOS? [70] [71]
June 1986?1 MbitPSRAMToshiba?CMOS? [72]
1986?4 MbitDRAMNEC800 nmNMOS99 mm² [60]
Texas Instruments, Toshiba1,000 nmCMOS100137 mm²
1987?16 MbitDRAMNTT700 nmCMOS148 mm² [60]
October 1988?512 kbitHSDRAMIBM1,000 nmCMOS78 mm² [73]
1991?64 MbitDRAM Matsushita, Mitsubishi, Fujitsu, Toshiba400 nmCMOS? [50]
1993?256 MbitDRAMHitachi, NEC 250 nm CMOS?
1995?4 MbitDPRAM (VRAM)Hitachi?CMOS? [55]
January 9, 1995?1 Gbit DRAMNEC250 nmCMOS? [74] [55]
Hitachi160 nmCMOS?
1996?4 Mbit FRAM Samsung ?NMOS? [75]
1997?4 Gbit QLC NEC150 nmCMOS? [50]
1998?4 GbitDRAMHyundai?CMOS? [56]
June 2001TC51W3216XB32 MbitPSRAM Toshiba ?CMOS? [76]
February 2001?4 GbitDRAMSamsung 100 nm CMOS? [50] [77]


Synchronous dynamic random-access memory (SDRAM)
Date of introductionChip nameCapacity (bits) [78] SDRAM typeManufacturer(s) Process MOSFET AreaRef
1992KM48SL200016 Mbit SDR Samsung ? CMOS ? [79] [22]
1996MSM5718C5018 Mbit RDRAM Oki ?CMOS325 mm2 [80]
N64 RDRAM 36 MbitRDRAM NEC ?CMOS? [81]
?1024 MbitSDR Mitsubishi 150 nm CMOS? [50]
1997?1024 MbitSDR Hyundai ? SOI ? [56]
1998MD576480264 MbitRDRAMOki?CMOS325 mm2 [80]
March 1998Direct RDRAM72 MbitRDRAM Rambus ?CMOS? [82]
June 1998?64 Mbit DDR Samsung?CMOS? [83] [84] [85]
1998?64 MbitDDRHyundai?CMOS? [56]
128 MbitSDRSamsung?CMOS? [86] [84]
1999?128 MbitDDRSamsung?CMOS? [84]
1024 MbitDDRSamsung 140 nm CMOS? [50]
2000 GS eDRAM 32 Mbit eDRAM Sony, Toshiba 180 nm CMOS279 mm2 [87]
2001?288 MbitRDRAMHynix?CMOS? [88]
? DDR2 Samsung 100 nm CMOS? [85] [50]
2002?256 MbitSDRHynix?CMOS? [88]
2003 EE+GS eDRAM 32 MbiteDRAMSony, Toshiba 90 nm CMOS86 mm2 [87]
?72 Mbit DDR3 Samsung90 nmCMOS? [89]
512 MbitDDR2Hynix?CMOS? [88]
Elpida 110 nm CMOS? [90]
1024 MbitDDR2Hynix?CMOS? [88]
2004?2048 MbitDDR2Samsung80 nmCMOS? [91]
2005 EE+GS eDRAM 32 MbiteDRAMSony, Toshiba 65 nm CMOS86 mm2 [92]
Xenos eDRAM 80 MbiteDRAMNEC90 nmCMOS? [93]
?512 MbitDDR3Samsung80 nmCMOS? [85] [94]
2006?1024 MbitDDR2Hynix60 nmCMOS? [88]
2008?? LPDDR2 Hynix?
April 2008?8192 MbitDDR3Samsung50 nmCMOS? [95]
2008?16384 MbitDDR3Samsung50 nmCMOS?
2009??DDR3Hynix 44 nm CMOS? [88]
2048 MbitDDR3Hynix 40 nm
2011?16384 MbitDDR3Hynix40 nmCMOS? [96]
2048 Mbit DDR4 Hynix 30 nm CMOS? [96]
2013?? LPDDR4 Samsung 20 nm CMOS? [96]
2014?8192 MbitLPDDR4Samsung20 nmCMOS? [97]
2015?12 GbitLPDDR4Samsung20 nmCMOS? [86]
2018?8192 Mbit LPDDR5 Samsung 10 nm FinFET ? [98]
128 GbitDDR4Samsung10 nmFinFET? [99]


Synchronous graphics random-access memory (SGRAM) and High Bandwidth Memory (HBM)
Date of introductionChip nameCapacity (bits) [78] SDRAM typeManufacturer(s) Process MOSFET AreaRef
November 1994HM52832068 Mbit SGRAM (SDR) Hitachi 350 nm CMOS 58 mm2 [100] [101]
December 1994μPD4818508 MbitSGRAM (SDR) NEC ?CMOS280 mm2 [102] [103]
1997μPD481165016 MbitSGRAM (SDR)NEC350 nmCMOS280 mm2 [104] [105]
September 1998?16 MbitSGRAM (GDDR) Samsung ?CMOS? [83]
1999KM4132G11232 MbitSGRAM (SDR)Samsung?CMOS? [106]
2002?128 MbitSGRAM (GDDR2)Samsung?CMOS? [107]
2003?256 MbitSGRAM (GDDR2)Samsung?CMOS? [107]
March 2005K4D553238F256 MbitSGRAM (GDDR)Samsung?CMOS77 mm2 [108]
October 2005?256 MbitSGRAM (GDDR4)Samsung?CMOS? [109]
2005?512 MbitSGRAM (GDDR4) Hynix ?CMOS? [88]
2007?1024 MbitSGRAM (GDDR5)Hynix 60 nm
2009?2048 MbitSGRAM (GDDR5)Hynix 40 nm
2010K4W1G1646G1024 MbitSGRAM (GDDR3)Samsung?CMOS100 mm2 [110]
2012?4096 MbitSGRAM (GDDR3) SK Hynix ?CMOS? [96]
2013?? HBM
March 2016MT58K256M32JA8 GbitSGRAM (GDDR5X) Micron 20 nmCMOS140 mm2 [111]
June 2016?32 Gbit HBM2 Samsung 20 nm CMOS? [112] [113]
2017?64 GbitHBM2Samsung20 nmCMOS? [112]
January 2018K4ZAF325BM16 GbitSGRAM (GDDR6)Samsung 10 nm FinFET ? [114] [115] [116]

See also

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DDR SDRAM Type of computer memory

Double Data Rate Synchronous Dynamic Random-Access Memory 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, DDR4 SDRAM and DDR5 SDRAM. None of its successors are forward or backward compatible with DDR1 SDRAM, meaning DDR2, DDR3, DDR4 and DDR5 memory modules will not work in DDR1-equipped motherboards, and vice versa.

Flash memory Electronic non-volatile computer storage device

Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. NAND flash and NOR flash use the same cell design, consisting of floating gate MOSFETs. They differ at the circuit level: in NAND flash, the relationship between the bit line and the word lines resembles a NAND gate; in NOR flash, it resembles a NOR gate; this depends on whether the state of the bit line or word lines is pulled high or low.

Static random-access memory Type of computer memory

Static random-access memory is a type of random-access memory (RAM) that uses latching circuitry (flip-flop) to store each bit. SRAM is volatile memory; data is lost when power is removed.

Dynamic random-access memory Type of computer memory

Dynamic random-access memory 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 Type of computer memory

Synchronous dynamic random-access memory is any DRAM where the operation of its external pin interface is coordinated by an externally supplied clock signal.

DDR2 SDRAM Second generation of double-data-rate synchronous dynamic random-access memory

Double Data Rate 2 Synchronous Dynamic Random-Access Memory is a double data rate (DDR) synchronous dynamic random-access memory (SDRAM) interface. It superseded the original DDR SDRAM specification, and was itself superseded by DDR3 SDRAM. DDR2 DIMMs are neither forward compatible with DDR3 nor backward compatible with DDR.

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 MOS transistors per memory cell, and dynamic RAM (DRAM), which uses a MOS transistor and a MOS capacitor per cell. Non-volatile memory uses floating-gate memory cells, which consist of a single floating-gate MOS transistor per cell.

Ferroelectric RAM Novel type of computer memory

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.The F-RAM chip contains a thin ferroelectric film of lead zirconate titanate, commonly referred to as PZT. The atoms in the PZT change polarity in an electric field, thereby producing a power efficient binary switch. However, the most important aspect of the PZT is that it is not affected by power disruption or magnetic interference, making F-RAM a reliable nonvolatile 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 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 SDRAM, an abbreviation for Graphics Double Data Rate 4 Synchronous Dynamic Random-Access Memory, is a type of graphics card memory (SGRAM) 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.

Transistor count Number of transistors in a device

The transistor count is the number of transistors in an electronic device. It typically refers to the number of MOSFETs on an integrated circuit (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.

GDDR5 SDRAM Type of high performance DRAM graphics card memory

Graphics Double Data Rate 5 Synchronous Dynamic Random-Access Memory is a 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.

Graphics DDR SDRAM is a type of synchronous dynamic random-access memory (SDRAM) specifically designed for graphics processing units (GPUs). GDDR SDRAM is distinct from the more widely known types of DDR SDRAM, such as DDR4, although they share some of the same features—including double data rate data transfers. As of 2018, GDDR SDRAM has been succeeded by GDDR2, GDDR3, GDDR4, GDDR5, GDDR5X, GDDR6, and GDDR6X.

Read-only memory Electronic memory that cannot be changed

Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing software that is rarely changed during the life of the system, also known as firmware. Software applications for programmable devices can be distributed as plug-in cartridges containing ROM.

Double Data Rate 4 Synchronous Dynamic Random-Access Memory is a type of synchronous dynamic random-access memory with a high bandwidth interface.

Memory cell (computing) Part of computer memory

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.

High Bandwidth Memory Type of memory used on processors that require high speed memory

High Bandwidth Memory (HBM) is a high-speed computer memory interface for 3D-stacked synchronous dynamic random-access memory (SDRAM) initially from Samsung, AMD and SK Hynix. It is used in conjunction with high-performance graphics accelerators, network devices, high-performance datacenter AI ASICs and FPGAs and in some supercomputers. The first HBM memory chip was produced by SK Hynix in 2013, and the first devices to use HBM were the AMD Fiji GPUs in 2015.


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