Qimonda began sampling 512Mb GDDR 5 memory silicon in November 2007 and now, six months on, it's ready to ship the chip in volume - if anyone wants it, that is.

Like past GDDR revisions, GDDR 5 ups the maximum available data transfer rate between video memory and GPU, in this case to 20GB/s.

Error compensation, adaptive interface timing and the ability to adapt the signalling characteristics to match patterns in the data being sent over the bus all contribute to the higher transfer rate.

The upshot is the ability to stick memory clocked to 4.5GHz onto a graphics card. Qimonda's product list also includes 3.6GHz and 4.0GHz versions.

Today, most mid-range and top-end graphics cards use GDDR 3. Some AMD parts also support GDDR 4, but Nvidia's don't.

That's because the performance advantage over GDDR 3 doesn't yet warrant the extra cost. Qimonda claims its GDDR 5 chips yield 2-3 times the performance of GDDR 3, and is banking that the likes of AMD and Nvidia decide that such a boost is sufficient to justify the premium the new memory will inevitably carry.

Hynix touted a 1Gb GDDR 5 chip just days after Qimonda's 512Mb-is-sampling announcement. That part is due to go into mass-production by the end of June if Hynix's claimed release schedule is to be stuck to.

Like Qimonda's memory, Hynix's part has a bandwidth of 20GB/s. Samsung announced a 24GB/s GDDR 5 chip in December 2007.