![]() ![]() Most DDR SDRAM operates at a voltage of 2.5 V, compared to 3.3 V for SDRAM. These two specifications are notched very similarly and care must be taken during insertion if unsure of a correct match. DDR SDRAM for notebook computers, SO-DIMMs, have 200 pins, which is the same number of pins as DDR2 SO-DIMMs. ĭDR SDRAM modules for desktop computers, dual in-line memory modules (DIMMs), have 184 pins (as opposed to 168 pins on SDRAM, or 240 pins on DDR2 SDRAM), and can be differentiated from SDRAM DIMMs by the number of notches (DDR SDRAM has one, SDRAM has two). A module's clock speed designates the data rate at which it is guaranteed to perform, hence it is guaranteed to run at lower ( underclocking) and can possibly run at higher ( overclocking) clock rates than those for which it was made. Modules are instead designed to run at different clock frequencies: for example, a PC-1600 module is designed to run at 100 MHz, and a PC-2100 is designed to run at 133 MHz. There is no architectural difference between DDR SDRAM modules. The package sizes in which DDR SDRAM is manufactured are also standardized by JEDEC. All RAM data rates in-between or above these listed specifications are not standardized by JEDEC – often they are simply manufacturer optimizations using tighter tolerances or overvolted chips. Note: All items listed above are specified by JEDEC as JESD79F. ![]() ![]() To mitigate the resulting bus signaling rate drop and overcome the memory bottleneck, new chipsets employ the multi-channel architecture. The chip select signal is used to issue commands to specific rank.Īdding modules to the single memory bus creates additional electrical load on its drivers. All ranks are connected to the same memory bus (address + data). The term sides would also be confusing because it incorrectly suggests the physical placement of chips on the module. A memory module may bear more than one rank. The term was introduced to avoid confusion with chip internal rows and banks. Multiple chips with common address lines are called a memory rank. For instance, the 64-bit data bus for DIMM requires eight 8-bit chips, addressed in parallel. To increase memory capacity and bandwidth, chips are combined on a module. Specification Single generic DDR memory module Four DDR RAM slots Corsair DDR-400 memory with heat spreaders Physical DDR layout Comparison of memory modules for portable/mobile PCs ( SO-DIMM) Modules The first retail PC motherboard using DDR SDRAM was released in August 2000. The first specification is for memory chips, and the second is for memory modules. JEDEC has set standards for the data rates of DDR SDRAM, divided into two parts. The development of DDR began in 1996, before its specification was finalized by JEDEC in June 2000 (JESD79). Samsung demonstrated the first DDR memory prototype in 1997, and released the first commercial DDR SDRAM chip (64 Mbit) in June 1998, followed soon after by Hyundai Electronics (now SK Hynix) the same year. In the late 1980s IBM had built DRAMs using a dual-edge clocking feature and presented their results at the International Solid-State Circuits Convention in 1990. ![]() Thus, with a bus frequency of 100 MHz, DDR SDRAM gives a maximum transfer rate of 1600 MB/s. With data being transferred 64 bits at a time, DDR SDRAM gives a transfer rate (in bytes/s) of (memory bus clock rate) × 2 (for dual rate) × 64 (number of bits transferred) / 8 (number of bits/byte). The name "double data rate" refers to the fact that a DDR SDRAM with a certain clock frequency achieves nearly twice the bandwidth of a SDR SDRAM running at the same clock frequency, due to this double pumping. One advantage of keeping the clock frequency low is that it reduces the signal integrity requirements on the circuit board connecting the memory to the controller. The interface uses double pumping (transferring data on both the rising and falling edges of the clock signal) to double data bus bandwidth without a corresponding increase in clock frequency. Implementations often have to use schemes such as phase-locked loops and self-calibration to reach the required timing accuracy. None of its successors are forward or backward compatible with DDR1 SDRAM, meaning DDR2, DDR3, DDR4 and DDR5 memory modules will not work on DDR1-equipped motherboards, and vice versa.Ĭompared to single data rate ( SDR) SDRAM, the DDR SDRAM interface makes higher transfer rates possible through more strict control of the timing of the electrical data and clock signals. DDR SDRAM, also retroactively called DDR1 SDRAM, has been superseded by DDR2 SDRAM, DDR3 SDRAM, DDR4 SDRAM and DDR5 SDRAM. Double Data Rate Synchronous Dynamic Random-Access Memory ( DDR SDRAM) is a double data rate (DDR) synchronous dynamic random-access memory (SDRAM) class of memory integrated circuits used in computers. ![]()
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