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DDR
Double data rate is a type of SDRAM in which data is sent on both the rising and falling edges of clock cycles in a data burst. It is usually referred to as DDR as opposed to DDR SDRAM.

DDR-2
DDR2-SDRAM is high-performance main memory. Over its predecessor. DDR2-SDRAM offers new features and functions that enable higher a clock rate and data rate operations of 400 MHz, 533 MHz, 667 MHz, and above. DDR2 transfers 64 bits of data twice every clock cycle. DDR2-SDRAM memory is not compatible with current DDR-SDRAM memory slots.

DDR-3
DDR3, (Double Data Rate 3 Synchronous Dynamic Random Access Memory), is the name of the new DDR memory standard that is being developed as the successor to DDR2 SDRAM. Theoretically, these modules could transfer data at the effective clockrate of 800 MHz, 1066 MHz, 1333 MHz, 1600 MHz and 1866MHz.

Die
An individual rectangular pattern on a wafer that contains circuitry to perform a specific function. Die are encapsulated to form the black chips that are then placed on a module.

DIMM
Dual inline memory module. A module with signal and power pins on both sides of the board (front and back).

Downgraded DRAM
Downgraded DRAM are Downgraded (off-spec DRAM not meeting full data sheet specification) DRAM memory. These are untested and unmarked.

Double-Rank
Defines 2 sets of DRAM chips (on a module) each comprised of 8 byte wide (64bits) data, or 9 bytes (72 bits) with ECC. All devices in a Rank are connected by a single Chip-Select. The actual memory size is not defined. Normally a module will have one rank per PCB side. Dual-rank modules can be used if a server supports them. These modules generall offer the best price/performance point but can limit overal system capacity or restrict future upgrade options.

DRAM
Dynamic random access memory. A type of memory component used to store information in a computer system. "Dynamic" means the DRAMs need a constant "refresh" (pulse of current through all of the memory cells) to keep the stored information. (See also RAM and SRAM.)

Dual Banked
A memory module with two banks or rows. See Bank.

Dual-Voltage RS-MMC (DV RS-MMC)
Dual-Voltage RS-MMC or DV RS-MMC refers to reduced-size MMCs that support dual-voltage (3V and 1.8V) operation. MMCmobile Cards in the reduced-size card form factor are required to support dual voltage operation.

Dynamic
Type of RAM (random access memory). To keep data in the DRAM, this data needs to be "refreshed" (recharged). The electric charge fades out of a DRAM like air seeps out of a balloon. Because of this change, it is called "dynamic."