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88-562: The Ace Plus contains a 1 GHz Qualcomm S1 processor, paired with 512 MB of RAM . It features a single camera on the back equipped with autofocus. The device also includes GPS, microUSB 2.0, Bluetooth, Wi-Fi, an FM radio, 3 GB of internal memory, and a microSD slot capable of supporting up to 32 GB of external memory. The Galaxy Ace Plus runs Android Ice Cream Sandwich . The Ace Plus incorporates Samsung ’s ChatON . Users can text each other, start multi-person conversations, and share multimedia files using their phone numbers. ChatON

176-469: A cache will generally access memory in units of cache lines . To transfer a 64-byte cache line requires eight consecutive accesses to a 64-bit DIMM, which can all be triggered by a single read or write command by configuring the SDRAM chips, using the mode register, to perform eight-word bursts . A cache line fetch is typically triggered by a read from a particular address, and SDRAM allows the "critical word" of

264-464: A read command is issued, the SDRAM will produce the corresponding output data on the DQ lines in time for the rising edge of the clock a few clock cycles later, depending on the configured CAS latency. Subsequent words of the burst will be produced in time for subsequent rising clock edges. A write command is accompanied by the data to be written driven on to the DQ lines during the same rising clock edge. It

352-565: A "quick contacts" feature in which the users can quickly access specific contacts. Social Hub combines the users' email accounts with social networking platforms so that all incoming emails are collected in one list. Users can mark them as favorites and have shortcuts to reply to emails. The Ace Plus has an app called A-GPS, which offers similar functionality to Google Maps . It offers voice-guided navigation in certain countries and displays instructions elsewhere. Random-access memory Random-access memory ( RAM ; / r æ m / )

440-556: A command is directed toward. Many commands also use an address presented on the address input pins. Some commands, which either do not use an address, or present a column address, also use A10 to select variants. The SDR SDRAM commands are defined as follows: All SDRAM generations (SDR and DDRx) use essentially the same commands, with the changes being: As an example, a 512 MB SDRAM DIMM (which contains 512 MB), might be made of eight or nine SDRAM chips, each containing 512 Mbit of storage, and each one contributing 8 bits to

528-585: A common identifier for 100 MHz SDRAM modules, and modules are now commonly designated with "PC"-prefixed numbers (PC66, PC100 or PC133 - although the actual meaning of the numbers has changed). All commands are timed relative to the rising edge of a clock signal. In addition to the clock, there are six control signals, mostly active low , which are sampled on the rising edge of the clock: SDRAM devices are internally divided into either two, four or eight independent internal data banks. One to three bank address inputs (BA0, BA1 and BA2) are used to select which bank

616-550: 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 . 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

704-467: 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

792-424: 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 four 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

880-404: 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. Sometimes, the contents of

968-466: A read command is issued on cycle 0, another read command is issued on cycle 2, and the CAS latency is 3, then the first read command will begin bursting data out during cycles 3 and 4, then the results from the second read command will appear beginning with cycle 5. If the command issued on cycle 2 were burst terminate, or a precharge of the active bank, then no output would be generated during cycle 5. Although

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1056-486: A read of that row into the bank's array of all 16,384 column sense amplifiers. This is also known as "opening" the row. This operation has the side effect of refreshing the dynamic (capacitive) memory storage cells of that row. Once the row has been activated or "opened", read and write commands are possible to that row. Activation requires a minimum amount of time, called the row-to-column delay, or t RCD before reads or writes to it may occur. This time, rounded up to

1144-551: 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

1232-425: A rising edge of its clock input. In SDRAM families standardized by JEDEC , the clock signal controls the stepping of an internal finite-state machine that responds to incoming commands. These commands can be pipelined to improve performance, with previously started operations completing while new commands are received. The memory is divided into several equally sized but independent sections called banks , allowing

1320-405: A row is an automatic side effect of activating it, there is a minimum time for this to happen, which requires a minimum row access time t RAS delay between an active command opening a row, and the corresponding precharge command closing it. This limit is usually dwarfed by desired read and write commands to the row, so its value has little effect on typical performance. The no operation command

1408-529: A single MOS transistor per capacitor. The first commercial DRAM IC chip, the 1K Intel 1103 , was introduced in October 1970. Synchronous dynamic random-access memory (SDRAM) was reintroduced with the Samsung KM48SL2000 chip in 1992. Early computers used relays , mechanical counters or delay lines for main memory functions. Ultrasonic delay lines were serial devices which could only reproduce data in

1496-406: A sufficient number of auto refresh commands (one per row, 8192 in the example we have been using) every refresh interval (t REF = 64 ms is a common value). All banks must be idle (closed, precharged) when this command is issued. As mentioned, the clock enable (CKE) input can be used to effectively stop the clock to an SDRAM. The CKE input is sampled each rising edge of the clock, and if it is low,

1584-491: 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

1672-593: 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

1760-424: Is a form of electronic 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 and magnetic tape ), where

1848-615: 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 writable. Within

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1936-683: Is also available in registered varieties, for systems that require greater scalability such as servers and workstations . Today, the world's largest manufacturers of SDRAM include Samsung Electronics , SK Hynix , Micron Technology , and Nanya Technology . There are several limits on DRAM performance. Most noted is the read cycle time, the time between successive read operations to an open row. This time decreased from 10 ns for 100 MHz SDRAM (1 MHz = 10 6 {\displaystyle 10^{6}}  Hz) to 5 ns for DDR-400, but remained relatively unchanged through DDR2-800 and DDR3-1600 generations. However, by operating

2024-463: Is always permitted, while the load mode register command requires that all banks be idle, and a delay afterward for the changes to take effect. The auto refresh command also requires that all banks be idle, and takes a refresh cycle time t RFC to return the chip to the idle state. (This time is usually equal to t RCD +t RP .) The only other command that is permitted on an idle bank is the active command. This takes, as mentioned above, t RCD before

2112-464: Is any DRAM where the operation of its external pin interface is coordinated by an externally supplied clock signal . DRAM integrated circuits (ICs) produced from the early 1970s to the early 1990s used an asynchronous interface, in which input control signals have a direct effect on internal functions delayed only by the trip across its semiconductor pathways. SDRAM has a synchronous interface, whereby changes on control inputs are recognised after

2200-623: Is encoded on the bank address pins during the load mode register command. For example, DDR2 SDRAM has a 13-bit mode register, a 13-bit extended mode register No. 1 (EMR1), and a 5-bit extended mode register No. 2 (EMR2). It is possible to refresh a RAM chip by opening and closing (activating and precharging) each row in each bank. However, to simplify the memory controller, SDRAM chips support an "auto refresh" command, which performs these operations to one row in each bank simultaneously. The SDRAM also maintains an internal counter, which iterates over all possible rows. The memory controller must simply issue

2288-403: Is far more expensive than the dynamic RAM used for larger memories. Static RAM also consumes far more power. 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,

2376-424: Is like power down, but the SDRAM uses an on-chip timer to generate internal refresh cycles as necessary. The clock may be stopped during this time. While self-refresh mode consumes slightly more power than power-down mode, it allows the memory controller to be disabled entirely, which commonly more than makes up the difference. SDRAM designed for battery-powered devices offers some additional power-saving options. One

2464-513: Is lost if power is removed. The two main types of volatile random-access semiconductor memory are static random-access memory (SRAM) and dynamic random-access memory (DRAM). Non-volatile RAM has also been developed and other types of non-volatile memories allow random access for read operations, but either do not allow write operations or have other kinds of limitations. These include most types of ROM and NOR flash memory . The use of semiconductor RAM dates back to 1965 when IBM introduced

2552-465: 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

2640-721: Is not inherently lower (faster access times) than asynchronous DRAM. Indeed, early SDRAM was somewhat slower than contemporaneous burst EDO DRAM due to the additional logic. The benefits of SDRAM's internal buffering come from its ability to interleave operations to multiple banks of memory, thereby increasing effective bandwidth . Today, virtually all SDRAM is manufactured in compliance with standards established by JEDEC , an electronics industry association that adopts open standards to facilitate interoperability of electronic components. JEDEC formally adopted its first SDRAM standard in 1993 and subsequently adopted other SDRAM standards, including those for DDR , DDR2 and DDR3 SDRAM . SDRAM

2728-472: Is preferred by Intel for its microprocessors. If the requested column address is at the start of a block, both burst modes (sequential and interleaved) return data in the same sequential sequence 0-1-2-3-4-5-6-7. The difference only matters if fetching a cache line from memory in critical-word-first order. Single data rate SDRAM has a single 10-bit programmable mode register. Later double-data-rate SDRAM standards add additional mode registers, addressed using

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2816-489: Is reduced by the size of the shadowed ROMs. The ' memory wall is the growing disparity of speed between CPU and the response time of memory (known as memory latency ) 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 off-chip memory response time only improved at 10%. Given these trends, it

2904-408: Is similar to the iPhone ’s iMessage and BlackBerry ’s BlackBerry Messenger . The Ace Plus features the upgraded GUI and TouchWiz 4.0 interface. The lock screen and menus are designed backgrounds. Users can have up to 7 unique home screens. They can be rearranged, deleted, or added at any point as the user wishes. The Ace Plus features a phone book with a cloud syncing feature. It also offers

2992-534: Is temperature-dependent refresh; an on-chip temperature sensor reduces the refresh rate at lower temperatures, rather than always running it at the worst-case rate. Another is selective refresh, which limits self-refresh to a portion of the DRAM array. The fraction which is refreshed is configured using an extended mode register. The third, implemented in Mobile DDR (LPDDR) and LPDDR2 is "deep power down" mode, which invalidates

3080-490: Is the duty of the memory controller to ensure that the SDRAM is not driving read data on to the DQ lines at the same time that it needs to drive write data on to those lines. This can be done by waiting until a read burst has finished, by terminating a read burst, or by using the DQM control line. When the memory controller needs to access a different row, it must first return that bank's sense amplifiers to an idle state, ready to sense

3168-402: Is the following word if an even address was specified, and the previous word if an odd address was specified. For the sequential burst mode , later words are accessed in increasing address order, wrapping back to the start of the block when the end is reached. So, for example, for a burst length of four, and a requested column address of five, the words would be accessed in the order 5-6-7-4. If

3256-442: Is the heart of a read operation, as it involves the careful sensing of the tiny signals in DRAM memory cells; it is the slowest phase of memory operation. However, once a row is read, subsequent column accesses to that same row can be very quick, as the sense amplifiers also act as latches. For reference, a row of a 1 Gbit DDR3 device is 2,048 bits wide, so internally 2,048 bits are read into 2,048 separate sense amplifiers during

3344-423: 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

3432-570: The Atanasoff–Berry Computer , the Williams tube and the Selectron tube . In 1966, Robert Dennard invented modern DRAM architecture for which there is a single MOS transistor per capacitor. 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

3520-432: The 1960s with bipolar memory, which used bipolar transistors . Although it was faster, it could not compete with the lower price of magnetic core memory. In 1957, Frosch and Derick manufactured the first silicon dioxide field-effect transistors at Bell Labs, the first transistors in which drain and source were adjacent at the surface. Subsequently, in 1960, a team demonstrated a working MOSFET at Bell Labs. This led to

3608-501: 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

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3696-540: 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

3784-473: The DIMM's 64- or 72-bit width. A typical 512 Mbit SDRAM chip internally contains four independent 16 MB memory banks. Each bank is an array of 8,192 rows of 16,384 bits each. (2048 8-bit columns). A bank is either idle, active, or changing from one to the other. The active command activates an idle bank. It presents a two-bit bank address (BA0–BA1) and a 13-bit row address (A0–A12), and causes

3872-462: The DQ lines to the SDRAM in time for the write operation. Because the effects of DQM on read data are delayed by two cycles, but the effects of DQM on write data are immediate, DQM must be raised (to mask the read data) beginning at least two cycles before write command but must be lowered for the cycle of the write command (assuming the write command is intended to have an effect). Doing this in only two clock cycles requires careful coordination between

3960-449: The MOS transistor could control writing the charge to the capacitor. This led to his development of a single-transistor DRAM memory cell. 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   μm MOS process with a capacity of 1   kbit , and

4048-486: 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 be quickly 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

4136-444: The RAM device, multiplexing and demultiplexing circuitry is used to select memory cells. Typically, a RAM device has a set of address lines A 0 , A 1 , . . . A n {\displaystyle A_{0},A_{1},...A_{n}} , 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

4224-422: The SDRAM automatically enters power-down mode, consuming minimal power until CKE is raised again. This must not last longer than the maximum refresh interval t REF , or memory contents may be lost. It is legal to stop the clock entirely during this time for additional power savings. Finally, if CKE is lowered at the same time as an auto-refresh command is sent to the SDRAM, the SDRAM enters self-refresh mode. This

4312-525: The SDRAM's mode register and expected by the DRAM controller. Any value may be programmed, but the SDRAM will not operate correctly if it is too low. At higher clock rates, the useful CAS latency in clock cycles naturally increases. 10–15 ns is 2–3 cycles (CL2–3) of the 200 MHz clock of DDR-400 SDRAM, CL4-6 for DDR2-800, and CL8-12 for DDR3-1600. Slower clock cycles will naturally allow lower numbers of CAS latency cycles. SDRAM modules have their own timing specifications, which may be slower than those of

4400-575: 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

4488-423: The bank address pins. For SDR SDRAM, the bank address pins and address lines A10 and above are ignored, but should be zero during a mode register write. The bits are M9 through M0, presented on address lines A9 through A0 during a load mode register cycle. Later (double data rate) SDRAM standards use more mode register bits, and provide additional mode registers called "extended mode registers". The register number

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4576-521: The burst length were eight, the access order would be 5-6-7-0-1-2-3-4. This is done by adding a counter to the column address, and ignoring carries past the burst length. The interleaved burst mode computes the address using an exclusive or operation between the counter and the address. Using the same starting address of five, a four-word burst would return words in the order 5-4-7-6. An eight-word burst would be 5-4-7-6-1-0-3-2. Although more confusing to humans, this can be easier to implement in hardware, and

4664-486: The cache line to be transferred first. ("Word" here refers to the width of the SDRAM chip or DIMM, which is 64 bits for a typical DIMM.) SDRAM chips support two possible conventions for the ordering of the remaining words in the cache line. Bursts always access an aligned block of BL consecutive words beginning on a multiple of BL. So, for example, a four-word burst access to any column address from four to seven will return words four to seven. The ordering, however, depends on

4752-456: The chips on the module. When 100 MHz SDRAM chips first appeared, some manufacturers sold "100 MHz" modules that could not reliably operate at that clock rate. In response, Intel published the PC100 standard, which outlines requirements and guidelines for producing a memory module that can operate reliably at 100 MHz. This standard was widely influential, and the term "PC100" quickly became

4840-405: 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

4928-438: The data to be written into the memory array. For a pipelined read, the requested data appears a fixed number of clock cycles (latency) after the read command, during which additional commands can be sent. The earliest DRAMs were often synchronized with the CPU clock (clocked) and were used with early microprocessors. In the mid-1970s, DRAMs moved to the asynchronous design, but in the 1990s returned to synchronous operation. In

5016-448: The development of metal–oxide–semiconductor (MOS) memory by John Schmidt at Fairchild Semiconductor in 1964. In addition to higher speeds, 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

5104-408: The device are used to activate the correct device that is being accessed. RAM is often byte addressable, although it is also possible to make RAM that is word-addressable. 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

5192-457: The device to operate on a memory access command in each bank simultaneously and speed up access in an interleaved fashion. This allows SDRAMs to achieve greater concurrency and higher data transfer rates than asynchronous DRAMs could. Pipelining means that the chip can accept a new command before it has finished processing the previous one. For a pipelined write, the write command can be immediately followed by another command without waiting for

5280-437: The dominant memory technology in the early 1970s. 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

5368-410: 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 fastest possible average access time 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,

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5456-401: The following rising edge of the clock is ignored for all purposes other than checking CKE. As long as CKE is low, it is permissible to change the clock rate, or even stop the clock entirely. If CKE is lowered while the SDRAM is performing operations, it simply "freezes" in place until CKE is raised again. If the SDRAM is idle (all banks precharged, no commands in progress) when CKE is lowered,

5544-412: 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

5632-609: The gap between RAM and hard disk speeds, although RAM continues to be an order of magnitude faster, with single-lane DDR5 8000MHz capable of 128 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. Synchronous dynamic random-access memory Synchronous dynamic random-access memory ( synchronous dynamic RAM or SDRAM )

5720-484: The interface circuitry at increasingly higher multiples of the fundamental read rate, the achievable bandwidth has increased rapidly. Another limit is the CAS latency , the time between supplying a column address and receiving the corresponding data. Again, this has remained relatively constant at 10–15 ns through the last few generations of DDR SDRAM. In operation, CAS latency is a specific number of clock cycles programmed into

5808-421: The interrupting read may be to any active bank, a precharge command will only interrupt the read burst if it is to the same bank or all banks; a precharge command to a different bank will not interrupt a read burst. Interrupting a read burst by a write command is possible, but more difficult. It can be done if the DQM signal is used to suppress output from the SDRAM so that the memory controller may drive data over

5896-601: The late 1980s IBM invented DDR SDRAM, they built a dual-edge clocking RAM and presented their results at the International Solid-State Circuits Convention in 1990. In 1998, Samsung released a double data rate SDRAM, known as DDR SDRAM , chip (64   Mbit ) followed soon after by Hyundai Electronics (now SK Hynix ) the same year and mass-produced in 1993. By 2000, SDRAM had replaced virtually all other types of DRAM in modern computers, because of its greater performance. SDRAM latency

5984-541: 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

6072-500: The memory and requires a full reinitialization to exit from. This is activated by sending a "burst terminate" command while lowering CKE. DDR SDRAM employs prefetch architecture to allow quick and easy access to multiple data words located on a common physical row in the memory. The prefetch architecture takes advantage of the specific characteristics of memory accesses to DRAM. Typical DRAM memory operations involve three phases: bitline precharge, row access, column access. Row access

6160-436: The memory cannot be altered. Writable variants of ROM (such as EEPROM and NOR flash ) share properties of both ROM and RAM, enabling data to persist without power and to be updated without requiring special equipment. 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,

6248-467: The monolithic (single-chip) 16-bit SP95 SRAM chip for their System/360 Model 95 computer, and Toshiba used bipolar DRAM memory cells for its 180-bit Toscal BC-1411 electronic calculator , both based on bipolar transistors . While it offered higher speeds than magnetic-core memory , bipolar DRAM could not compete with the lower price of the then-dominant magnetic-core memory. In 1966, Dr. Robert Dennard invented modern DRAM architecture in which there's

6336-495: The next multiple of the clock period, specifies the minimum number of wait cycles between an active command, and a read or write command. During these wait cycles, additional commands may be sent to other banks; because each bank operates completely independently. Both read and write commands require a column address. Because each chip accesses eight bits of data at a time, there are 2,048 possible column addresses thus requiring only 11 address lines (A0–A9, A11). When

6424-426: The next row. This is known as a "precharge" operation, or "closing" the row. A precharge may be commanded explicitly, or it may be performed automatically at the conclusion of a read or write operation. Again, there is a minimum time, the row precharge delay, t RP , which must elapse before that row is fully "closed" and so the bank is idle in order to receive another activate command on that bank. Although refreshing

6512-443: The order it was written. Drum memory could be expanded at relatively low cost but efficient retrieval of memory items requires knowledge of the physical layout of the drum to optimize speed. Latches built out of triode vacuum tubes , 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

6600-571: The paging file form the system's total memory. (For example, if a computer has 2 GB (1024 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"

6688-577: 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 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 ~7 GB/s via NVMe / PCIe in 2024, closing

6776-421: The requested address, and the configured burst type option: sequential or interleaved. Typically, a memory controller will require one or the other. When the burst length is one or two, the burst type does not matter. For a burst length of one, the requested word is the only word accessed. For a burst length of two, the requested word is accessed first, and the other word in the aligned block is accessed second. This

6864-420: The row is fully open and can accept read and write commands. When a bank is open, there are four commands permitted: read, write, burst terminate, and precharge. Read and write commands begin bursts, which can be interrupted by following commands. A read, burst terminate, or precharge command may be issued at any time after a read command, and will interrupt the read burst after the configured CAS latency. So if

6952-435: The same type, simply because it takes longer for signals to traverse a larger circuit. Constructing a memory unit of many gibibytes with a response time of one clock cycle is difficult or impossible. Today's CPUs often still have a mebibyte of 0 wait state cache memory, but it resides on the same chip as the CPU cores due to the bandwidth limitations of chip-to-chip communication. It must also be constructed from static RAM, which

7040-400: 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, it is not random access; it behaves much like a hard disc drive if somewhat slower. Aside, unlike CD-RW or DVD-RW , DVD-RAM does not need to be erased before reuse. The memory cell is

7128-443: 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. 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 where stored information

7216-401: The time the SDRAM takes to turn off its output on a clock edge and the time the data must be supplied as input to the SDRAM for the write on the following clock edge. If the clock frequency is too high to allow sufficient time, three cycles may be required. If the read command includes auto-precharge, the precharge begins the same cycle as the interrupting command. A modern microprocessor with

7304-558: 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

7392-494: Was Samsung's 64   Mbit 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   Mbit 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. This form of RAM

7480-490: Was expected that memory latency would become an overwhelming bottleneck in computer performance. Another reason for the disparity is the enormous increase in the size of memory since the start of the PC revolution in the 1980s. Originally, PCs contained less than 1 mebibyte of RAM, which often had a response time of 1 CPU clock cycle, meaning that it required 0 wait states. Larger memory units are inherently slower than smaller ones of

7568-410: Was introduced in 1965, used a form of capacitor-bipolar DRAM, storing 180-bit data on discrete memory cells , consisting of germanium bipolar transistors and capacitors. While it offered higher speeds than magnetic-core memory, bipolar DRAM could not compete with the lower price of the then dominant magnetic-core memory. Capacitors had also been used for earlier memory schemes, such as the drum of

7656-460: Was possible. Magnetic core memory was the standard form of computer memory until displaced by 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. Semiconductor memory appeared in

7744-433: Was released in 1970. The earliest DRAMs were often synchronized with the CPU clock (clocked) and were used with early microprocessors. In the mid-1970s, DRAMs moved to the asynchronous design, but in the 1990s returned to synchronous operation. In 1992 Samsung released KM48SL2000, which had a capacity of 16   Mbit . and mass-produced in 1993. The first commercial DDR SDRAM ( double data rate SDRAM) memory chip

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