DDR2 belong to the recent DDR SDRAM (double data rate synchronous dynamic random access memory) family of RAMs. The second member of this family was the DDR2. And, DDR3 is the member, which followed DDR2. GDDR5 (Graphics Double Data Rate, version 5) SGRAM falls in to the category of DRAM graphics card memories. GDDR5 is based on the JEDEC standards. More importantly, GDDR5 is based on DDR3 RAM. Its predecessor GDDR4 (Graphics Double Data Rate, version 4) was based on DDR2 RAM.
What is DDR2?
DDR2 SDRAM stands for double data rate type two synchronous dynamic random access memory. It is the second member in the DDR family (which was followed by DDR3 RAM). However, DDR2 RAM is neither backward compatible with DDR nor forward compatible with DDR3 RAM. That means you need different type of motherboards for DDR/ DDR2/ DDR3 RAMs. It uses double pumping to transfer data on both the edges of the clock signal (this is a characteristic of RAMs in the DDR family). DDR2 RAM provides a performance of four data transfers per clock cycle. Therefore DDR2 can provide a maximum transfer rate of 3200 MB/s (with a base clock speed of 100Mhz).
What is GDDR5?
GDDR5 stands for Graphics Double Data Rate, version 5. It is a SGRAM. It falls to the category of DRAM graphics card memory. It is based on the JEDEC standards. It is specifically intended for the computer applications that requires a high bandwidth. GDDR5 is the successor to GDDR4. But, GGDR5 is based on DDR3 SDRAM memory (unlike the GDDR4 that was based on DDR2 RAM). Therefore, GDDR5 has twice the amount of data lines present in GDDR4. However, both GDDR5 and GDDR4 have 8-bit wide prefetch buffers. GDDR5 has a data transfer speed of 2 data words of 32-bit width per write clock. GDDR5 can operate with two types of clocks. They are CK (differential command clock) and WCK (forward differential clock). CK acts as a reference for address and command, while WCK acts as a reference for data reads/writes. CK runs at half the frequency of WCK. A spin-off of Infineon called Qimonda started volume production of 512 Mbit GDDR5 (at 3.6Gbit, 4 Gbit and 4.5 Gbit) in 2008. The first ever 1 Gib GDDR was introduced by Hynix semiconductor. A bandwidth of 20 GB/s (on a 32-bit bus) can be supported with that Hynix GDDR5. The newly developed Hynix GDDR5 (2 Gbit) is claimed to be the fastest memory in the market today. The first ever company to ship GDDR5 memory based products was AMD (in 2008). Their Radeon HD 4870 VGA series used Qimondas’ 512 Mbit modules.
What is the difference between GDDR5 and DDR2?
GDDR5 is a SGRAM, while DDR2 is a SDRAM. Therefore, it is not 100% accurate to compare these two types of RAMs. However, GDDR5 is based on DDR3 SDRAM. And DDR3 has twice the amount of data lines present in DDR2. DDR3 RAM can transfer data at a rate that is twice as fast as DDR2 RAM. In general, DDR3 has a high bandwidth compared to DDR2. So, it is safe to say the when it come to bandwidth (and therefore speed), GDDR5 is ahead of DDR2 by a considerable margin.