@ravi_9793
Larger buffer has nothin to do with sata 1 or 2.
Its just the amount of RAM allocated on a HDD to buffer data before writing on disc.
Sata 2 has theoritical 300MBPS data transfer speed whereas SATA1 has onle 150 MBPS. But ny normal HDD wont even use half of the bandwidth. But its always better to go future proof, so get sata2 HDD.
Seagate 160GB sata2 [8MB buffer]: 2.6k
Seagate 250 Gb sata2 [16MB buffer]: 3.5k
Hitachi 250 GB sata2[8MB buffer]: 3.6k
The 250 GB has better bang for the bucks and perfomance wise also its better as its got 16MB buffer.