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Double Data Rate 4 Synchronous Dynamic Random-Access Memory (DDR4 SDRAM) is a type of synchronous dynamic random-access memory with a high bandwidth ("double data rate") interface. Released to the market in 2014, [ 2 ] [ 3 ] [ 4 ] it is a variant of dynamic random-access memory (DRAM), some of which have been in use since the early 1970s, [ 5 ...
Assorted SO-DIMM Modules A 200-pin PC2-5300 DDR2 SO-DIMM. A 204-pin PC3-10600 DDR3 SO-DIMM. A SO-DIMM slot on a computer motherboard. A SO-DIMM (pronounced "so-dimm" / ˈ s oʊ d ɪ m /, also spelled "SODIMM") or small outline DIMM, is a smaller alternative to a DIMM, being roughly half the physical size of a regular DIMM. The first SODIMMs had ...
DDR3 and DDR4 use A12 during read and write command to indicate "burst chop", half-length data transfer; DDR4 changes the encoding of the activate command. A new signal ACT controls it, during which the other control lines are used as row address bits 16, 15 and 14. When ACT is high, other commands are the same as above.
A comparison of the standard (top) and low-profile UniDIMM version (bottom). The standard UniDIMM version has the same dimensions as DDR4 SO-DIMMs. [1]: 28 UniDIMM (short for Universal DIMM) is a specification for dual in-line memory modules (DIMMs), which are printed circuit boards (PCBs) designed to carry dynamic random-access memory (DRAM) chips
The 8n prefetch architecture is combined with an interface designed to transfer two data words per clock cycle at the I/O pins. A single read or write operation for the DDR4 SDRAM consists of a single 8n-bit-wide 4-clock data transfer at the internal DRAM core and 8 corresponding n-bit-wide half-clock-cycle data transfers at the I/O pins. [20]
Normally, there is a performance penalty for using registered memory. Each read or write is buffered for one cycle between the memory bus and the DRAM, so the registered RAM can be thought of as running one clock cycle behind the equivalent unregistered DRAM.
The memory width specifies the data width of the memory module interface in bits. For example, 64 would indicate a 64-bit data width, as is found on non-ECC DIMMs common in SDR and DDR1–4 families of RAM. A memory of width of 72 would indicate an ECC module, with 8 extra bits in the data width for the error-correcting code syndrome.
The standards specify the physical and electrical characteristics of the modules, and include the data for computer simulations of the memory module operating in a system. [ 10 ] Memory modules of the DDR2-SDRAM type are available for laptop, desktop, and server computers in a wide selection of capacities and access speeds.