I think we have to explain everything in laymen terms and use a
story to let people understand how the hard disk operates and why
the need to defrag.
To make things short and simple, the media in the hard disk where
all data are written and stored and retrieved are divided into
sectors and each sectors has some form of register or numbering for
the write head to address, reach before accessing it to write or
read data. When you have a new hard disk without any data or
information in it, the write head will always access the media from
inside out, from the smaller internal diameter of the media (FYI
the media is round like a CD/ DVD-r) outwards to the largest outer
diameter. When you delete any data written meanwhile, the space in
between the data will be empty and accessible for new data writes.
so when you save something onto your hard disks again right after
the deletion the read/ write head will place data onto that sector
with tagged access information. If that space is too small for your
data file the remainder of the data shall be placed on a new sector
further out of the media and away from the initial string. thus
your data are fragmented but this allows the hard disks to maintain
its write speed. later when the data are to be retreived or
accessed, it may take the read head a little longer when it seeks
the file in fragmented sectors as compared to continuous read out
over datas that are placed consecutively in a chuck of sectors.
Disk defragmentation is a periodic maintenance tool that moves such
data and group them orderly so that read speed of hard disks can be
maintained and keep the overall performance of your computer in
check. Remember, the slowest device in your computer is always the
hard disk drive because it is the only device that transfer data
through mechanical means. the motherboard and other cards in your
computer somehow moves data in the in smaller steps of electrical
waves called signals.
