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#alternate Wikipedia (en)
Random-access memory
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Form of computer data storage
"RAM" redirects here. For other uses, see Ram.
Not to be confused with Random Access Memories or Random-access
machine.
Computer memory and data storage types
General
* Memory cell
* Memory coherence
* Cache coherence
* Memory hierarchy
* Memory access pattern
* Memory map
* Secondary storage
* MOS memory
+ floating-gate
* Continuous availability
* Areal density (computer storage)
* Block (data storage)
* Object storage
* Direct-attached storage
* Network-attached storage
+ Storage area network
+ Block-level storage
* Single-instance storage
* Data
* Structured data
* Unstructured data
* Big data
* Metadata
* Data compression
* Data corruption
* Data cleansing
* Data degradation
* Data integrity
* Data security
* Data validation
* Data validation and reconciliation
* Data recovery
* Storage
* Data cluster
* Directory
* Shared resource
* File sharing
* File system
* Clustered file system
* Distributed file system
* Distributed file system for cloud
* Distributed data store
* Distributed database
* Database
* Data bank
* Data storage
* Data store
* Data deduplication
* Data structure
* Data redundancy
* Replication (computing)
* Memory refresh
* Storage record
* Information repository
* Knowledge base
* Computer file
* Object file
* File deletion
* File copying
* Backup
* Core dump
* Hex dump
* Data communication
* Information transfer
* Temporary file
* Copy protection
* Digital rights management
* Volume (computing)
* Boot sector
* Master boot record
* Volume boot record
* Disk array
* Disk image
* Disk mirroring
* Disk aggregation
* Disk partitioning
* Memory segmentation
* Locality of reference
* Logical disk
* Storage virtualization
* Virtual memory
* Memory-mapped file
* Software entropy
* Software rot
* In-memory database
* In-memory processing
* Persistence (computer science)
* Persistent data structure
* RAID
* Non-RAID drive architectures
* Memory paging
* Bank switching
* Grid computing
* Cloud computing
* Cloud storage
* Fog computing
* Edge computing
* Dew computing
* Amdahl's law
* Moore's law
* Kryder's law
Volatile
RAM
* Hardware cache
+ CPU cache
+ Scratchpad memory
* DRAM
+ eDRAM
+ SDRAM
+ SGRAM
+ LPDDR
+ QDRSRAM
+ EDO DRAM
+ XDR DRAM
+ RDRAM
+ SDRAM
+ DDR
+ GDDR
+ HBM
* SRAM
+ 1T-SRAM
* ReRAM
* QRAM
* Content-addressable memory (CAM)
* VRAM
* Dual-ported RAM
+ Video RAM (dual-ported DRAM)
Historical
* Williams-Kilburn tube (1946-1947)
* Delay-line memory (1947)
* Mellon optical memory (1951)
* Selectron tube (1952)
* Dekatron
* T-RAM (2009)
* Z-RAM (2002-2010)
Non-volatile
ROM
* MROM
* PROM
+ EPROM
+ EEPROM
* ROM cartridge
* Solid-state storage (SSS)
+ Flash memory is used in:
+ Solid-state drive (SSD)
+ Solid-state hybrid drive (SSHD)
+ USB flash drive
+ IBM FlashSystem
+ Flash Core Module
* Memory card
+ Memory Stick
+ CompactFlash
+ PC Card
+ MultiMediaCard
+ SD card
+ SIM card
+ SmartMedia
+ Universal Flash Storage
+ SxS
+ MicroP2
+ XQD card
* Programmable metallization cell
NVRAM
* Memistor
* Memristor
* PCM (3D XPoint)
* MRAM
* Electrochemical RAM (ECRAM)
* Nano-RAM
* CBRAM
Early stage NVRAM
* FeRAM
* ReRAM
* FeFET memory
Analog recording
* Phonograph cylinder
* Phonograph record
* Quadruplex videotape
* Vision Electronic Recording Apparatus
* Magnetic recording
+ Magnetic storage
+ Magnetic tape
+ Magnetic tape data storage
+ Tape drive
+ Tape library
+ Digital Data Storage (DDS)
+ Videotape
+ Videocassette
+ Cassette tape
+ Linear Tape-Open
+ Betamax
+ 8 mm video format
+ DV
+ MiniDV
+ MicroMV
+ U-matic
+ VHS
+ S-VHS
+ VHS-C
+ D-VHS
* Hard disk drive
Optical
* 3D optical data storage
+ Optical disc
+ LaserDisc
+ Compact Disc Digital Audio (CDDA)
+ CD
+ CD Video
+ CD-R
+ CD-RW
+ Video CD
+ Super Video CD
+ Mini CD
+ Nintendo optical discs
+ CD-ROM
+ Hyper CD-ROM
+ DVD
+ DVD+R
+ DVD-Video
+ DVD card
+ DVD-RAM
+ MiniDVD
+ HD DVD
+ Blu-ray
+ Ultra HD Blu-ray
+ Holographic Versatile Disc
* WORM
In development
* CBRAM
* Racetrack memory
* NRAM
* Millipede memory
* ECRAM
* Patterned media
* Holographic data storage
+ Electronic quantum holography
* 5D optical data storage
* DNA digital data storage
* Universal memory
* Time crystal
* Quantum memory
Historical
* Paper data storage (1725)
* Punched card (1725)
* Punched tape (1725)
* Plugboard
* Delay-line memory
* Drum memory (1932)
* Magnetic-core memory (1949)
* Plated wire memory (1957)
* Core rope memory (1960s)
* Thin-film memory (1962)
* Disk pack (1962)
* Twistor memory (~1968)
* Bubble memory (~1970)
* Floppy disk (1971)
* v
* t
* e
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 (RAM; /raem/) 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.
[ ]
Contents
* 1 History
+ 1.1 MOS RAM
* 2 Types
* 3 Memory cell
* 4 Addressing
* 5 Memory hierarchy
* 6 Other uses of RAM
+ 6.1 Virtual memory
+ 6.2 RAM disk
+ 6.3 Shadow RAM
* 7 Recent developments
* 8 Memory wall
* 9 Timeline
+ 9.1 SRAM
+ 9.2 DRAM
+ 9.3 SDRAM
+ 9.4 SGRAM and HBM
* 10 See also
* 11 References
* 12 External links
History
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
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]
MOS RAM
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 um 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]
Types
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
Main article: Memory cell (computing)
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)
DRAM Cell (1 Transistor and one capacitor)
Addressing
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
Main article: 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.
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
Main article: 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 (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.
RAM disk
Main article: RAM drive
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 * 2^10 bytes) chip was
manufactured with 0.18 um technology in the summer of 2003.^[citation
needed] In June 2004, Infineon Technologies unveiled a 16 MB (16
* 2^20 bytes) prototype again based on 0.18 um 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 * 2^30 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]
Timeline
See also: Flash memory S: Timeline, Read-only memory S: Timeline, and
Transistor count S: Memory
SRAM
CAPTION: Static random-access memory (SRAM)
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 ^[9]
1965 ? 8-bit ? Bipolar IBM ? N/A
SP95 16-bit ? Bipolar IBM ? N/A ^[40]
? 64-bit ? MOSFET Fairchild ? PMOS ^[41]
1966 TMC3162 16-bit ? Bipolar (TTL) Transitron ? N/A ^[8]
? ? ? MOSFET NEC ? ? ^[42]
1968 ? 64-bit ? MOSFET Fairchild ? PMOS ^[42]
144-bit ? MOSFET NEC ? NMOS
512-bit ? MOSFET IBM ? NMOS ^[41]
1969 ? 128-bit ? Bipolar IBM ? N/A ^[9]
1101 256-bit 850 ns MOSFET Intel 12,000 nm PMOS ^[43]^[44]^[45]^[46]
1972 2102 1 kbit ? MOSFET Intel ? NMOS ^[43]
1974 5101 1 kbit 800 ns MOSFET Intel ? CMOS ^[43]^[47]
2102A 1 kbit 350 ns MOSFET Intel ? NMOS (depletion) ^[43]^[48]
1975 2114 4 kbit 450 ns MOSFET Intel ? NMOS ^[43]^[47]
1976 2115 1 kbit 70 ns MOSFET Intel ? NMOS (HMOS) ^[43]^[44]
2147 4 kbit 55 ns MOSFET Intel ? NMOS (HMOS) ^[43]^[49]
1977 ? 4 kbit ? MOSFET Toshiba ? CMOS ^[44]
1978 HM6147 4 kbit 55 ns MOSFET Hitachi 3,000 nm CMOS (twin-well) ^[49]
TMS4016 16 kbit ? MOSFET Texas Instruments ? NMOS ^[44]
1980 ? 16 kbit ? MOSFET Hitachi, Toshiba ? CMOS ^[50]
64 kbit ? MOSFET Matsushita
1981 ? 16 kbit ? MOSFET Texas Instruments 2,500 nm NMOS ^[50]
October 1981 ? 4 kbit 18 ns MOSFET Matsushita, Toshiba 2,000 nm CMOS
^[51]
1982 ? 64 kbit ? MOSFET Intel 1,500 nm NMOS (HMOS) ^[50]
February 1983 ? 64 kbit 50 ns MOSFET Mitsubishi ? CMOS ^[52]
1984 ? 256 kbit ? MOSFET Toshiba 1,200 nm CMOS ^[50]^[45]
1987 ? 1 Mbit ? MOSFET Sony, Hitachi, Mitsubishi, Toshiba ? CMOS ^[50]
December 1987 ? 256 kbit 10 ns BiMOS Texas Instruments 800 nm BiCMOS
^[53]
1990 ? 4 Mbit 15-23 ns MOSFET NEC, Toshiba, Hitachi, Mitsubishi ? CMOS
^[50]
1992 ? 16 Mbit 12-15 ns MOSFET Fujitsu, NEC 400 nm
December 1994 ? 512 kbit 2.5 ns MOSFET IBM ? CMOS (SOI) ^[54]
1995 ? 4 Mbit 6 ns Cache (SyncBurst) Hitachi 100 nm CMOS ^[55]
256 Mbit ? MOSFET Hyundai ? CMOS ^[56]
DRAM
CAPTION: Dynamic random-access memory (DRAM)
Date of introduction Chip name Capacity (bits) DRAM type
Manufacturer(s) Process MOSFET Area Ref
1965 N/A 1 bit DRAM (cell) Toshiba N/A N/A N/A ^[16]^[17]
1967 N/A 1 bit DRAM (cell) IBM N/A MOS N/A ^[19]^[42]
1968 ? 256 bit DRAM (IC) Fairchild ? PMOS ? ^[8]
1969 N/A 1 bit DRAM (cell) Intel N/A PMOS N/A ^[42]
1970 1102 1 kbit DRAM (IC) Intel, Honeywell ? PMOS ? ^[42]
1103 1 kbit DRAM Intel 8,000 nm PMOS 10 mm^2 ^[57]^[58]^[20]
1971 mPD403 1 kbit DRAM NEC ? NMOS ? ^[59]
? 2 kbit DRAM General Instrument ? PMOS 13 mm^2 ^[60]
1972 2107 4 kbit DRAM Intel ? NMOS ? ^[43]^[61]
1973 ? 8 kbit DRAM IBM ? PMOS 19 mm^2 ^[60]
1975 2116 16 kbit DRAM Intel ? NMOS ? ^[62]^[8]
1977 ? 64 kbit DRAM NTT ? NMOS 35 mm^2 ^[60]
1979 MK4816 16 kbit PSRAM Mostek ? NMOS ? ^[63]
? 64 kbit DRAM Siemens ? VMOS 25 mm^2 ^[60]
1980 ? 256 kbit DRAM NEC, NTT 1,000-1,500 nm NMOS 34-42 mm^2 ^[60]
1981 ? 288 kbit DRAM IBM ? MOS 25 mm^2 ^[64]
1983 ? 64 kbit DRAM Intel 1,500 nm CMOS 20 mm^2 ^[60]
256 kbit DRAM NTT ? CMOS 31 mm^2
January 5, 1984 ? 8 Mbit DRAM Hitachi ? MOS ? ^[65]^[66]
February 1984 ? 1 Mbit DRAM Hitachi, NEC 1,000 nm NMOS 74-76 mm^2
^[60]^[67]
NTT 800 nm CMOS 53 mm^2 ^[60]^[67]
1984 TMS4161 64 kbit DPRAM (VRAM) Texas Instruments ? NMOS ? ^[68]^[69]
January 1985 mPD41264 256 kbit DPRAM (VRAM) NEC ? NMOS ? ^[70]^[71]
June 1986 ? 1 Mbit PSRAM Toshiba ? CMOS ? ^[72]
1986 ? 4 Mbit DRAM NEC 800 nm NMOS 99 mm^2 ^[60]
Texas Instruments, Toshiba 1,000 nm CMOS 100-137 mm^2
1987 ? 16 Mbit DRAM NTT 700 nm CMOS 148 mm^2 ^[60]
October 1988 ? 512 kbit HSDRAM IBM 1,000 nm CMOS 78 mm^2 ^[73]
1991 ? 64 Mbit DRAM Matsushita, Mitsubishi, Fujitsu, Toshiba 400 nm
CMOS ? ^[50]
1993 ? 256 Mbit DRAM Hitachi, NEC 250 nm CMOS ?
1995 ? 4 Mbit DPRAM (VRAM) Hitachi ? CMOS ? ^[55]
January 9, 1995 ? 1 Gbit DRAM NEC 250 nm CMOS ? ^[74]^[55]
Hitachi 160 nm CMOS ?
1996 ? 4 Mbit FRAM Samsung ? NMOS ? ^[75]
1997 ? 4 Gbit QLC NEC 150 nm CMOS ? ^[50]
1998 ? 4 Gbit DRAM Hyundai ? CMOS ? ^[56]
June 2001 TC51W3216XB 32 Mbit PSRAM Toshiba ? CMOS ? ^[76]
February 2001 ? 4 Gbit DRAM Samsung 100 nm CMOS ? ^[50]^[77]
SDRAM
Part of this section is transcluded from Synchronous dynamic
random-access memory. (edit | history)
CAPTION: Synchronous dynamic random-access memory (SDRAM)
Date of introduction Chip name Capacity (bits)^[78] SDRAM type
Manufacturer(s) Process MOSFET Area Ref
1992 KM48SL2000 16 Mbit SDR Samsung ? CMOS ? ^[79]^[22]
1996 MSM5718C50 18 Mbit RDRAM Oki ? CMOS 325 mm^2 ^[80]
N64 RDRAM 36 Mbit RDRAM NEC ? CMOS ? ^[81]
? 1024 Mbit SDR Mitsubishi 150 nm CMOS ? ^[50]
1997 ? 1024 Mbit SDR Hyundai ? SOI ? ^[56]
1998 MD5764802 64 Mbit RDRAM Oki ? CMOS 325 mm^2 ^[80]
March 1998 Direct RDRAM 72 Mbit RDRAM Rambus ? CMOS ? ^[82]
June 1998 ? 64 Mbit DDR Samsung ? CMOS ? ^[83]^[84]^[85]
1998 ? 64 Mbit DDR Hyundai ? CMOS ? ^[56]
128 Mbit SDR Samsung ? CMOS ? ^[86]^[84]
1999 ? 128 Mbit DDR Samsung ? CMOS ? ^[84]
1024 Mbit DDR Samsung 140 nm CMOS ? ^[50]
2000 GS eDRAM 32 Mbit eDRAM Sony, Toshiba 180 nm CMOS 279 mm^2 ^[87]
2001 ? 288 Mbit RDRAM Hynix ? CMOS ? ^[88]
? DDR2 Samsung 100 nm CMOS ? ^[85]^[50]
2002 ? 256 Mbit SDR Hynix ? CMOS ? ^[88]
2003 EE+GS eDRAM 32 Mbit eDRAM Sony, Toshiba 90 nm CMOS 86 mm^2 ^[87]
? 72 Mbit DDR3 Samsung 90 nm CMOS ? ^[89]
512 Mbit DDR2 Hynix ? CMOS ? ^[88]
Elpida 110 nm CMOS ? ^[90]
1024 Mbit DDR2 Hynix ? CMOS ? ^[88]
2004 ? 2048 Mbit DDR2 Samsung 80 nm CMOS ? ^[91]
2005 EE+GS eDRAM 32 Mbit eDRAM Sony, Toshiba 65 nm CMOS 86 mm^2 ^[92]
Xenos eDRAM 80 Mbit eDRAM NEC 90 nm CMOS ? ^[93]
? 512 Mbit DDR3 Samsung 80 nm CMOS ? ^[85]^[94]
2006 ? 1024 Mbit DDR2 Hynix 60 nm CMOS ? ^[88]
2008 ? ? LPDDR2 Hynix ?
April 2008 ? 8192 Mbit DDR3 Samsung 50 nm CMOS ? ^[95]
2008 ? 16384 Mbit DDR3 Samsung 50 nm CMOS ?
2009 ? ? DDR3 Hynix 44 nm CMOS ? ^[88]
2048 Mbit DDR3 Hynix 40 nm
2011 ? 16384 Mbit DDR3 Hynix 40 nm CMOS ? ^[96]
2048 Mbit DDR4 Hynix 30 nm CMOS ? ^[96]
2013 ? ? LPDDR4 Samsung 20 nm CMOS ? ^[96]
2014 ? 8192 Mbit LPDDR4 Samsung 20 nm CMOS ? ^[97]
2015 ? 12 Gbit LPDDR4 Samsung 20 nm CMOS ? ^[86]
2018 ? 8192 Mbit LPDDR5 Samsung 10 nm FinFET ? ^[98]
128 Gbit DDR4 Samsung 10 nm FinFET ? ^[99]
SGRAM and HBM
CAPTION: Synchronous graphics random-access memory (SGRAM) and High
Bandwidth Memory (HBM)
Date of introduction Chip name Capacity (bits)^[78] SDRAM type
Manufacturer(s) Process MOSFET Area Ref
November 1994 HM5283206 8 Mbit SGRAM (SDR) Hitachi 350 nm CMOS 58 mm^2
^[100]^[101]
December 1994 mPD481850 8 Mbit SGRAM (SDR) NEC ? CMOS 280 mm^2
^[102]^[103]
1997 mPD4811650 16 Mbit SGRAM (SDR) NEC 350 nm CMOS 280 mm^2
^[104]^[105]
September 1998 ? 16 Mbit SGRAM (GDDR) Samsung ? CMOS ? ^[83]
1999 KM4132G112 32 Mbit SGRAM (SDR) Samsung ? CMOS ? ^[106]
2002 ? 128 Mbit SGRAM (GDDR2) Samsung ? CMOS ? ^[107]
2003 ? 256 Mbit SGRAM (GDDR2) Samsung ? CMOS ? ^[107]
SGRAM (GDDR3)
March 2005 K4D553238F 256 Mbit SGRAM (GDDR) Samsung ? CMOS 77 mm^2
^[108]
October 2005 ? 256 Mbit SGRAM (GDDR4) Samsung ? CMOS ? ^[109]
2005 ? 512 Mbit SGRAM (GDDR4) Hynix ? CMOS ? ^[88]
2007 ? 1024 Mbit SGRAM (GDDR5) Hynix 60 nm
2009 ? 2048 Mbit SGRAM (GDDR5) Hynix 40 nm
2010 K4W1G1646G 1024 Mbit SGRAM (GDDR3) Samsung ? CMOS 100 mm^2 ^[110]
2012 ? 4096 Mbit SGRAM (GDDR3) SK Hynix ? CMOS ? ^[96]
2013 ? ? HBM
March 2016 MT58K256M32JA 8 Gbit SGRAM (GDDR5X) Micron 20 nm CMOS
140 mm^2 ^[111]
June 2016 ? 32 Gbit HBM2 Samsung 20 nm CMOS ? ^[112]^[113]
2017 ? 64 Gbit HBM2 Samsung 20 nm CMOS ? ^[112]
January 2018 K4ZAF325BM 16 Gbit SGRAM (GDDR6) Samsung 10 nm FinFET ?
^[114]^[115]^[116]
See also
* Technology portal
* CAS latency (CL)
* Hybrid Memory Cube
* Multi-channel memory architecture
* Registered/buffered memory
* RAM parity
* Memory Interconnect/RAM buses
* Memory geometry
* Chip creep
* Read-mostly memory (RMM)
* Electrochemical random-access memory
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External links
* Media related to RAM at Wikimedia Commons
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