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"DDR2" redirects here. For the video game, see Dance Dance Revolution 2ndMIX. Dance Dance Revolution 2ndMix, or 2ndMix, is the 2nd game in the Dance Dance Revolution series of Music video games
DRAM types

In electronic engineering, DDR2 SDRAM or double-data-rate two synchronous dynamic random access memory is a random access memory technology used for high speed storage of the working data of a computer or other digital electronic device. SDRAM refers to synchronous Dynamic random access memory, a term that is used to describe dynamic random access memory that has a synchronous interface SDRAM refers to synchronous Dynamic random access memory, a term that is used to describe dynamic random access memory that has a synchronous interface DDR SDRAM ( double data rate synchronous dynamic random access memory) is a class of memory Integrated circuit used in Computers It achieves nearly twice In Electronic engineering, DDR3 SDRAM or double-data-rate three Synchronous dynamic random access memory is a Random access memory Direct Rambus DRAM or DRDRAM (sometimes just called Rambus DRAM or RDRAM) is a type of synchronous dynamic RAM, designed by the Rambus XDR DRAM or extreme data rate Dynamic random access memory is a high-performance RAM interface and successor to the Rambus RDRAM it XDR2 DRAM is a type of Dynamic Random Access Memory that is offered by Rambus. V irtual C hannel R andom A ccess M emory ( VC-RAM GDDR3, Graphics Double Data Rate 3, is a graphics card-specific memory technology designed by ATI Technologies with the collaboration of JEDEC GDDR4 SDRAM (Graphics Double Data Rate version 4 is a type of Graphics card memory specified by the JEDEC Semiconductor Memory Standard GDDR5 (Graphics Double Data Rate version 5 is a type of Graphics card memory the standards of which were set out in the GDDR5 specification by JEDEC Electronic engineering is a discipline dealing with the behavior and effects of Electrons (as in electron tubes and transistors and with electronic devices systems or equipment In Computing, a Computer bus operating with double data rate transfers data on both the rising and falling edges of the Clock signal. SDRAM refers to synchronous Dynamic random access memory, a term that is used to describe dynamic random access memory that has a synchronous interface A computer is a Machine that manipulates data according to a list of instructions. Digital electronics are Electronics systems that use Digital signals Digital electronics are representations of Boolean algebra also see

It is a part of the SDRAM (synchronous dynamic random access memory) family of technologies, which is one of many DRAM (dynamic random access memory) implementations, and is an evolutionary improvement over its predecessor, DDR SDRAM. SDRAM refers to synchronous Dynamic random access memory, a term that is used to describe dynamic random access memory that has a synchronous interface DDR SDRAM ( double data rate synchronous dynamic random access memory) is a class of memory Integrated circuit used in Computers It achieves nearly twice

Its primary benefit is the ability to operate the external data bus twice as fast as DDR SDRAM. This is achieved by improved bus signaling, and by operating the memory cells at half the clock rate (one quarter of the data transfer rate), rather than at the clock rate as in the original DDR. In Telecommunication, signalling (UK spelling or signaling (US spelling has the following meanings The use of signals for controlling communications DDR2 memory at the same clock speed as DDR will provide the same bandwidth but markedly higher latency, providing worse performance. SDRAM latency refers to the delays incurred when a Computer tries to access Data in SDRAM.

Contents

Overview

Like all SDRAM implementations, DDR2 stores memory in memory cells that are activated with the use of a clock signal to synchronize their operation with an external data bus. In Electronics and especially synchronous Digital circuits a clock signal is a signal used to coordinate the actions of two or more circuits Like DDR before it, DDR2 cells transfer data both on the rising and falling edge of the clock (a technique called "dual pumping"). In Computing, a Computer bus operating with double data rate transfers data on both the rising and falling edges of the Clock signal. The key difference between DDR and DDR2 is that in DDR2 the bus is clocked at twice the speed of the memory cells, so four bits of data can be transferred per memory cell cycle. In Computer architecture, a bus is a subsystem that transfers data between computer components inside a Computer or between computers Thus, without speeding up the memory cells themselves, DDR2 can effectively operate at twice the bus speed of DDR.

DDR2's bus frequency is boosted by electrical interface improvements, on-die termination, prefetch buffers and off-chip drivers. The prefetch buffer is a memory cache located on modern RAM modules which stores data before it is actually needed However, latency is greatly increased as a trade-off. In Computing, memory latency is the time between initiating a request for a Byte or word in memory until it is retrieved The DDR2 prefetch buffer is 4 bits deep, whereas it is 2 bits deep for DDR and 8 bits deep for DDR3. In Electronic engineering, DDR3 SDRAM or double-data-rate three Synchronous dynamic random access memory is a Random access memory While DDR SDRAM has typical read latencies of between 2 and 3 bus cycles, DDR2 may have read latencies between 4 and 6 cycles. Thus, DDR2 memory must be operated at twice the bus speed to achieve the same latency.

Another cost of the increased speed is the requirement that the chips are packaged in a more expensive and more difficult to assemble BGA package as compared to the TSSOP package of the previous memory generations such as DDR SDRAM and SDR SDRAM. A ball grid array ( BGA) is a type of Surface-mount packaging used for Integrated circuits BGA The BGA is descended from the A TSSOP (Thin-Shrink Small Outline Package is a four-sided rectangular thin body size surface mount component DDR SDRAM ( double data rate synchronous dynamic random access memory) is a class of memory Integrated circuit used in Computers It achieves nearly twice SDRAM refers to synchronous Dynamic random access memory, a term that is used to describe dynamic random access memory that has a synchronous interface This packaging change was necessary to maintain signal integrity at higher speeds.

Power savings are achieved primarily due to an improved manufacturing process through die shrinkage, resulting in a drop in operating voltage (1. 8 V compared to DDR's 2. 5 V). The lower memory clock frequency may also enable power reductions in applications that do not require the highest available speed.

According to JEDEC[1] the maximum recommended voltage is 1. 9 volts and should be considered the absolute maximum when memory stability is an issue (such as in servers or other mission critical devices). In addition, JEDEC states that memory modules must withstand up to 2. 3 volts before incurring permanent damage (although they may not actually function correctly at that level).

Specification standards

Chips and modules

For use in computers, DDR2 SDRAM is supplied in DIMMs with 240 pins and a single locating notch. A DIMM, or dual in-line memory module, comprises a series of Dynamic random access memory Integrated circuits These modules are mounted on a Printed DIMMs are identified by their peak transfer capacity (often called bandwidth).

Standard name Memory clock Cycle time I/O Bus clock Data transfers per second Module name Peak transfer rate
DDR2-400 100 MHz 10 ns 200 MHz 400 Million PC2-3200 3200 MB/s
DDR2-533 133 MHz 7. A megabyte is a unit of Information or Computer storage equal to either 106 (1000000 Bytes or 220 (1048576 bytes depending on 5 ns 266 MHz 533 Million PC2-4200
PC2-43001		 4266 MB/s
DDR2-667 166 MHz 6 ns 333 MHz 667 Million PC2-5300
PC2-54001		 5333 MB/s
DDR2-800 200 MHz 5 ns 400 MHz 800 Million PC2-6400 6400 MB/s
DDR2-1066 266 MHz 3. 75 ns 533 MHz 1066 Million PC2-8500
PC2-86001		 8533 MB/s
DDR2-1300 325 MHz 3. 1 ns 650 MHz 1300 Million PC2-10400 10400 MB/s

Note: DDR2-xxx (or DDR-xxx) denotes data transfer rate, and describes raw DDR chips, whereas PC2-xxxx (or PC-xxxx) denotes theoretical bandwidth (though it is often rounded up or down), and is used to describe assembled DIMMs. Bandwidth is calculated by taking transfers per second and multiplying by eight. This is because DDR2 memory modules transfer data on a bus that is 64 data bits wide, and since a byte comprises 8 bits, this equates to 8 bytes of data per transfer.

1 Some manufacturers label their DDR2 sticks as PC2-4300 instead of PC2-4200, and PC2-5400 instead of PC2-5300. At least one manufacturer has reported this reflects successful testing at a faster-than standard speed,[2] whilst others simply use the alternate rounding as the name, as described above.

In addition to bandwidth and capacity variants, modules can

  1. Optionally implement ECC, which is an extra data byte lane used for correcting minor errors and detecting major errors for better reliability. Modules with ECC are identified by an additional ECC in their designation. PC2-4200 ECC is a PC2-4200 module with ECC.
  2. Be "registered", which improves signal integrity (and hence potentially clock speed and physical slot capacity) by electrically buffering the signals at a cost of an extra clock of increased latency. Those modules are identified by an additional R in their designation, whereas non-registered (a. k. a. "unbuffered") RAM may be identified by an additional U in the designation. PC2-4200R is a registered PC2-4200 module, PC2-4200R ECC is the same module but with additional ECC.
  3. Be Fully buffered modules, which are designated by F or FB and do not have the same notch position as other classes. Fully Buffered DIMM (or FB-DIMM is a memory technology which can be used to increase reliability speed and density of memory systems Fully buffered modules cannot be used with motherboards that are made for registered modules, and the different notch position physically prevents their insertion.

Note: registered and unbuffered SDRAM generally cannot be mixed on the same channel.

Debut

DDR2 was introduced in the second quarter of 2003 at two initial speeds: 200 MHz (referred to as PC2-3200) and 266 MHz (PC2-4200). Both performed worse than the original DDR specification due to higher latency, which made total access times longer. However, the original DDR technology tops out at speeds around 266 MHz (533 MHz effective). Faster DDR chips exist, but JEDEC has stated that they will not be standardized. JEDEC Solid State Technology Association, formerly known as J oint E lectron D evice E ngineering C ouncil ( JEDEC) or Joint These modules are mostly manufacturer optimizations of highest-yielding chips, drawing significantly more power than slower-clocked modules, and usually do not offer much, if any, greater real-world performance.

DDR2 started to become competitive with the older DDR standard by the end of 2004, as modules with lower latencies became available. [3]

Backward compatibility

Two PC2-6400 sticks with integrated heat sinks
Two PC2-6400 sticks with integrated heat sinks

DDR2 DIMMs are not designed to be backward compatible with DDR DIMMs. A heat sink (or heatsink) is an environment or object that absorbs and dissipates heat from another object using Thermal contact (either direct or radiant The notch on DDR2 DIMMs is in a different position than DDR DIMMs, and the pin density is slightly higher than DDR DIMMs in desktops. DDR2 is a 240-pin module, DDR is a 184-pin module. Notebooks have 200-pin modules for DDR and DDR2.

Faster DDR2 DIMMs are compatible with slower DDR2 DIMMs; however, the faster module runs at the slower module's speed. Using slower DDR2 memory in a system capable of higher speeds results in the bus running at the speed of the slowest memory in use.

Relation to GDDR memory

The first commercial product to claim using the "DDR2" technology was the NVIDIA GeForce FX 5800 graphics card. The multinational NVIDIA Corporation ( (ɪnˈvɪdiə specializes in the manufacture of graphics-processor technologies for Workstations The GeForce FX or "GeForce 5" series ( Codenamed NV30) is a line of Graphics cards from the manufacturer Nvidia. However, it is important to note that this GDDR-2 memory used on graphics cards is not DDR2 per se, but rather an early midpoint between DDR and DDR2 technologies. Using "DDR2" to refer to GDDR-2 is a colloquial misnomer. A colloquialism is an expression not used in formal speech, writing or Paralinguistics. A misnomer is a term which suggests an interpretation that is known to be untrue In particular, the performance-enhancing doubling of the I/O clock rate is missing. It had severe overheating issues due to the nominal DDR voltages. ATI has since designed the GDDR technology further into GDDR3, which is more true to the DDR2 specifications, though with several additions suited for graphics cards. GDDR3, Graphics Double Data Rate 3, is a graphics card-specific memory technology designed by ATI Technologies with the collaboration of JEDEC

GDDR3 is now commonly used in modern graphics cards and some tablet PCs. GDDR3, Graphics Double Data Rate 3, is a graphics card-specific memory technology designed by ATI Technologies with the collaboration of JEDEC However, further confusion has been added to the mix with the appearance of budget and mid-range graphics cards which claim to use "DDR2". These cards actually use standard DDR2 chips designed for use as main system memory. These chips cannot achieve the clock speeds that GDDR3 can but are inexpensive enough to be used as memory on mid-range cards.

See also

References

  1. ^ JEDEC JESD 208 (section 5, tables 15 and 16)
  2. ^ Mushkin PC2-5300 vs. Corsair PC2-5400
  3. ^ Ilya Gavrichenkov. Fully Buffered DIMM (or FB-DIMM is a memory technology which can be used to increase reliability speed and density of memory systems A SO-DIMM, or small outline dual in-line memory module, is a type of Computer memory built using Integrated circuits. Dual-channel architecture describes a technology that theoretically doubles data throughput from RAM to the memory controller. This is a list of device bandwidths: the Net bit rate (or more informally Digital bandwidth) of some computer devices employing methods of data transport is quantified CAS is an Abbreviation for column address strobe, or sometimes column address select, both referring to the column of the physical memory location In Electronic engineering, DDR3 SDRAM or double-data-rate three Synchronous dynamic random access memory is a Random access memory DDR SDRAM ( double data rate synchronous dynamic random access memory) is a class of memory Integrated circuit used in Computers It achieves nearly twice DDR2 vs. DDR: Revenge gained. X-bit Laboratories.

External links

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