Disk controllers since earliest ATA/IDE should be able to read or write up to 256 sectors (128KB) at a time with one command, and apparently with LBA48 it was expanded to 64K sectors (32MB!), so it's quite possible to saturate the bandwidth of the hardware, but the real bottleneck is at the filesystem level and above - only when reading/writing large amounts of data at once sequentially is this realised.