Comparison of SSD and HDD
There are presently two common types of internal drives. The more common drive is the hard
disk drive, while the solid state drive (SSD) is still making progress. One the outside there may
not appear to be much of a difference between a 2.5" hard drive and an SSD with the same form
factor. The connection to the motherboard is the same. The power connectors are the same. Even
the mounting to the computer case or laptop hard drive bay is usually the same. The difference is
in how the drives store and retrieve the information.
Hard disk drives consist of one or more round platters coated with a magnetic substance that can
store a magnetic field. As the platter rotates, a read or write head can move over the platter and
detect or change this magnetic field. Solid state drives do not have moving parts-hence the name.
Instead, a solid state drive uses NAND-based flash memory chips. These memory chips, much
like USB thumb drives, can retain their data even when there is no power. Instead of a moving
read or write head, information is stored by selecting which memory cell to store information to
and applying the desired value to that memory cell in terms of ones and zeros.
The hard drive is still the most common form of storage by far in today's computers because they
are cheaper - less than $200 for a terabyte when this is written. Because the hard disk drive must
rotate a platter and move a read or write head across the platter, there is a slight delay when
accessing data. This delay is called the seek time. If a file system becomes severely fragmented,
multiple seeks read reading and writing can greatly degrade performance.
In addition the hard drive can be more easily damaged. The read and write heads are so close to
the platter that if dust particles get on the platter, they can cause scratches and loss of data. Also,
dropping or bumping the hard disk drive can jar the read and write heads to to uch the platter,
causing damage to the heads and loss of data. For this