The HDD in any home computer is the most important storage device. It works on the principles of magnetic polarization. A metallic disk is spun by a motor and this makes sectors or parts of the disk pass under the head that reads and writes them as they move. Laptop HDDs are not any different in this sense, the only difference somebody can find is that they use less electricity and have a smaller general outer shell. These attributes contribute to their lower write and read speeds too. Notebook hard drives often use advanced power schemes to cut down on consumption and they are protected against shocks and falls. IBM notebook hard disk drives for instance recognize that the notebook is falling and put the head at a safe position before impact.
Most laptop hard drives operate at 5400 rounds per minute opposed to 7200 used by most of their desktop relatives, older models still work at 4200 rounds per minute. Regular size for a laptop HDD is 2.5″ disk diameter while desktop manufacturers tend to use 3.5″ disks. The smaller disks result in a more dense arrangement and that gives the head some extra work. For example slower rotation speeds had to be introduced so that the head can still pick up information from the disk with the tighter packed blocks. Most often used connector type for recent hard disks is SATA, which is a serial way of transferring data. As a consequence the controller chips became faster and less complicated and the old 80 wire ribbon cables could be swapped with the new thin 7 wire solution.
These portable hard drives usually have a smaller capacity, 160GB to 320GB is common, but more expensive models already have 500GB and bigger drives. Memory chip based drives called SSD are also available both for notebooks and desktop computers. These drives are way more expensive than a normal mechanical unit, but there are pros to them as well. They have no moving parts, for one, and that can significantly lowers power consumption. The technology used allows faster data access that makes reading of small scattered files faster by the magnitude. Read and write speeds on the long run also rival normal hard drives so they’re expected to take their place as soon as the price drops to an acceptable level.
A regular hard disk drive costs about $60 to $80 and as expected an SSD with 250GB capacity is about ten times as expensive as the normal version, at $698 they are still a bit steep.