That's hard to say because there are many factors influencing data throughput. According to Wikipedia, a 7200rpm drive will have a "sustained "disk-to-buffer" data transfer rate of about 70 megabytes per second" (http://en.wikipedia.org/wiki/Hard_disk#Other_characteristics
). It's not clear exactly how that number is achieved. I can't get solid numbers from data sheets. Different companies use different measuring metrics or different terminology (disk-to-buffer, host-to/from-drive, Sustained Data Rate OD, etc.). Seagate's Momentus® 7200.3 2.5" 7200rpm drives are rated 80 MB/s versus their Momentus 5400.5 2.5" 5400rpm drives at 61.3 MB/s (Sustained Internal Transfer Rate). Real world numbers should typically be lower.
There are many factors to take into account such as:
- Rotational speed of the disk. Higher is better, but many drives use slower speeds to balance power consumption (especially for notebooks), heat generation (SFF/game consoles), noise (HTPCs), and vibration.
- Location of the data on the platter. The outer edges can provide higher data transfer due to higher number of sectors per track.
- The density of the sectors on the disk. Newer, higher capacity platters can deliver higher transfer numbers due to the density of data per physical area unit compared to older designs. Linked to the physical diameter of the platter/disk where the larger surface area of a larger diameter platter (e.g. 3.5" vs. 2.5") can provide a higher density of sectors. This can sometimes make up for the fact that the disk is rotating slower. Compare the numbers of a 2TB 3.5" 7200rpm drive to that of a 300GB 2.5" 10000rpm one.
- The size and speed of the cache buffer. More important in certain circumstances (see below), but ideally it should be a minor factor.
- The fragmentation of the drive and location of the data fragments or files. Probably the biggest factor. A single large file will be read faster than many small files assuming that the large file is in one continuous chunk. If it is highly fragmented, then it's possible that the large file will get read no faster than the many small ones. A large buffer can be of some help. Obviously, defragging a hard drive can possibly gain you a huge increase in performance.
- The type of disk interface the drive is using. SATA is the current desktop speed king, but older PATA (EIDE) interfaces could bottleneck your system.