GDDR5 (Graphics Double Data Rate, version 5) SDRAM is a type of high performance DRAM graphics card memory designed for computer applications requiring high bandwidth. Unlike its predecessor, GDDR4, GDDR5 is based on DDR3 SDRAM memory which has double the data lines compared to DDR2 SDRAM, but GDDR5 also has 8-bit wide prefetch buffers similar to GDDR4.
GDDR5 SGRAM conforms to the standards which were set out in the GDDR5 specification by the JEDEC. It uses an 8n-prefetch architecture and DDR interface to achieve high performance operation and can be configured to operate in ×32 mode or ×16 (clamshell) mode which is detected during device initialization. The GDDR5 interface transfers two 32-bit wide data words per write clock (WCK) cycle to/from the I/O pins. Corresponding to the 8n-prefetch, a single write or read access consists of a 256-bit wide two CK clock cycle data transfer at the internal memory core and eight corresponding 32-bit wide one-half WCK clock cycle data transfers at the I/O pins.
GDDR5 operates with two different clock types. A differential command clock (CK) as a reference for address and command inputs, and a forwarded differential write clock (WCK) as a reference for data reads and writes. Being more precise, the GDDR5 SGRAM uses two write clocks, each of them assigned to two bytes. The WCK runs at twice the CK frequency. Taking a GDDR5 with 5 Gbit/s data rate per pin as an example, the CK clock runs with 1.25 GHz and WCK with 2.5 GHz. The CK and WCK clocks will be aligned during the initialization and training sequence. This alignment allows read and write access with minimum latency.
A single 32-bit GDDR5 chip has about 67 signal pins and the rest are power and grounds in the 170 BGA package.
Qimonda, a spin-off of Infineon, has demonstrated and sampled GDDR5,[1] and released a paper about the technologies behind GDDR5.[2] On May 10, 2008, Qimonda announced volume production of 512 Mbit GDDR5 modules rated at 3.6 Gbit/s (900 MHz), 4.0 Gbit/s (1 GHz), and 4.5 Gbit/s (1.125 GHz).[3]
Hynix Semiconductor introduced the industry's first 1 Gib GDDR5 memory. It supports a bandwidth of 20 GB/s on a 32-bit bus, which enables memory configurations of 1 GiB at 160 GB/s with only 8 circuits on a 256-bit bus. Hynix 2 Gbit GDDR5 boasts a 7 GHz clock speed. The newly developed GDDR5 is the fastest and highest density graphics memory available in the market. It operates at 7 GHz effective clock-speed and processes up to 28 GB/s with a 32-bit I/O. 2 Gbit GDDR5 memory chips will enable graphics cards with 2 GiB or more of onboard memory with 224 GB/s or higher peak bandwidth. The memory maker claims that the new chip will be in demand in the second half of 2010.
On June 25, 2008, AMD became the first company to ship products using GDDR5 memory with its Radeon HD 4870 video card series, incorporating Qimonda's 512 Mbit memory modules at 3.6 Gbit/s bandwidth.[4][5]
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