Toshiba has recently revealed that they are creating a hard drive that has a higher maximum areal density, allowing 160GB on a single side of a platter, rather than the usual 125GB, allowing 640GB of space to fit onto 2 data platters, up from the original 500GB. HDDs will be made available some time between October and December this year. The part number to watch out for will be M6465GSX.
Currently, the PlayStation 3 can only support hard drives upto 500GB, though the 2.5″ SATA drives are available up to 1TB though these drive are slightly larger than the HDD bay on the PlayStation 3. The reason the high-capacity HDDs are also physically larger is because they contain a third disc, or platter, holding the extra data. The practical limit for data storage on a single side of one platter has been around 125GB for a while now, with 500GB drives using both sides of two platters.