This time is called the seek time and is measured in milliseconds . There is also a small delay waiting for the appropriate section of the track to rotate under the head. This latency is much smaller than the seek time. Once the correct section of the track is under the head, successive bytes of information can be transferred to the main memory at rates of several megabytes per second. This discrepancy between the speed of access to the first byte required, and subsequent bytes on the same track means that it is not economic to transfer small numbers of bytes.
Transfers are usually of blocks of several hundred bytes or even more.
Notice that the access time to data stored in secondary storage will depend on its location. The hard disc will hold all the software that is required to run the computer, from the operating system to packages like word-processing and spreadsheet programs. All the user's data and programs will also be stored on the hard disc. In addition most computers have some form of removable storage device which can be used to save copies of important files etc. The most common device for this purpose is a floppy disc which has a very limited capacity.