What's in a DOS Article Index What's in a DOS How it works
Writing a file  A look at filing systems, blocks and the FAT and
how they are used    There is a big problem with disk drives.
No, not the constant running out of space that we used to suffer
from, but the deeper computer science and engineering problem of
actually making them useful at all.  We are so familiar with
disk drives being delivered to us in a usable form that it is
first necessary to go back to the raw hardware to see what the
problem is.   In a hard disk drive the data is stored on the
disk as magnetic patterns written in complete concentric tracks.
More accurately each track is split into a number of different
sectors and data can be read or written by specifying the head,
track and sector involved.  If you want to read head 2, track
10, sector 5 then the hard disk moves its head array to track 10
and reads the sector markers passing underneath head 2 until it
detects sector 5. Then, and only then, does it start reading
data and passing