random ram redirects here for the daft punk album see random access memories for other uses see ram disambiguation computer memory types volatile ram dram sram historical williamskilburn tube 194647 delay line memory 1947 mellon optical memory 1951 selectron tube 1952 dekatron tram 2009 zram 20022010 nonvolatile rom mask rom prom eprom eeprom flash memory nvram reram early stage nvram feram mram pcm magnetic magnetic tape hard disk drive optical optical disc in development cbram racetrack memory nram millipede memory fjg ram historical paper data storage 1725 drum memory 1932 magneticcore memory 1949 plated wire memory 1957 core rope memory 1960s thinfilm memory 1962 disk pack 1962 twistor memory 1968 bubble memory 1970 floppy disk 1971 vte example of writable volatile randomaccess memory synchronous dynamic ram modules primarily used as main memory in personal computers workstations and servers randomaccess memory ram rm is a form of computer data storage that stores data and machine code currently being used a randomaccess 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 directaccess data storage media such as hard disks cdrws dvdrws 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 8bit or 16bit etc devices in todays technology randomaccess memory takes the form of integrated circuits ram is normally associated with volatile types of memory such as dram modules where stored information is lost if power is removed although nonvolatile ram has also been developed other types of nonvolatile 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 norflash integratedcircuit ram chips came into the market in the early 1970s with the first commercially available dram chip the intel 1103 introduced in october 1970 history these ibm tabulating machines from the 1930s used mechanical counters to store information a portion of a core memory with a modern flash sd card on top 1 megabit chip one of the last models developed by veb carl zeiss jena in 1989 early computers used relays mechanical counters or delay lines for main memory functions ultrasonic delay lines 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 randomaccess 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 powerefficient 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 magneticcore memory was invented in 1947 and developed up until the mid1970s it became a widespread form of randomaccess memory relying on an array of magnetized rings by changing the sense of each rings 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 memory system until displaced by solidstate memory in integrated circuits starting in the early 1970s dynamic randomaccess memory dram allowed replacement of a 4 or 6transistor 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 the toshiba toscal bc1411 electronic calculator which was introduced in 1965 dram was then developed by robert h dennard in 1968 prior to the development of integrated readonly memory rom circuits permanent or readonly randomaccess memory was often constructed using diode matrices driven by address decoders or specially wound core rope memory planes 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 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 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 capacitors 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 readonly 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 solidstate drives ecc memory which can be either sram or dram includes special circuitry to detect andor correct random faults memory errors in the stored data using parity bits or error correction codes in general the term ram refers solely to solidstate memory devices either dram or sram and more specifically the main memory in most computers in optical storage the term dvdram is somewhat of a misnomer since unlike cdrw or dvdrw it does not need to be erased before reuse nevertheless a dvdram behaves much like a hard disc drive if somewhat slower memory cell 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 maintainedstored until it is changed by the setreset process the value in the memory cell can be accessed by reading it in sram the memory cell is a type of flipflop 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 memory hierarchy one can read and overwrite data in ram many computer systems have a memory hierarchy consisting of processor registers ondie 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 harddrives cdroms and several other parts of the computer system other uses of ram a 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 virtual memory most modern operating systems employ a method of extending ram capacity known as virtual memory a portion of the computers 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 systems total memory for example if a computer has 2 gb 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 ram drive software can partition a portion of a computers 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 shadow ram sometimes the contents of a relatively slow rom chip are copied to readwrite 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 writeprotected 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 bioss 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 recent developments several new types of nonvolatile 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 018m technology in the summer of 2003 nantero built a functioning carbon nanotube memory prototype 10gib 10230 bytes array in 2004 whether some of these technologies can eventually take significant market share from either dram sram or flashmemory technology however remains to be seen since 2006 solidstate 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 randomaccess memory and disks dramatically reducing the difference in performance some kinds of randomaccess memory such as ecoram are specifically designed for server farms where low power consumption is more important than speed 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 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 socalled 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 resistancecapacitance rc delays in signal transmission are growing as feature sizes shrink imposing an additional bottleneck that frequency increases dont 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 125 average annual cpu performance improvement between 2000 and 2014 a different concept is the processormemory 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 in contrast ram can be as fast as 5766 mbs vs 477 mbs for an ssd information technology portal technology portal cas latency cl hybrid memory cube multichannel memory architecture registeredbuffered memory ram parity memory interconnectram buses memory geometry chip creep media related to ram at wikimedia commons vtebasic computer componentsinput devices keyboard image scanner microphone pointing device graphics tablet joystick light pen mouse optical pointing stick touchpad touchscreen trackball refreshable braille display sound card webcam softcam video card output devices monitor refreshable braille display printer speakers plotter sound card video card removable data storage optical disc cd dvd bluray disk pack floppy disk memory card usb flash drive computer case central processing unit cpu hdd ssd sshd motherboard network interface controller power supply randomaccess memory ram fax modem expansion card ports ethernet firewire ieee 1394 parallel port serial port ps2 port usb thunderbolt displayport hdmi dvi vga esata audio jack authority control gnd 41769090 