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 touch the platter, causing damage to the heads and loss of data. For this reason, hard disk drives should not be moved while in use, and should be handled carefully even when not in use.
The solid state drive is more expensive, but because it has no moving parts, it is less fragile. Because data access is truly random accesses with virtually no seek times, it also has much lower performance degradation and is not sensitive to a fragmented file system. However, the memory cells in a solid state drive currently can't be written to as often as the magnetic platters in a hard disk drive. After writing a memory cell so many times, they wear out. Because of this, special technologies may be used to distribute writes across the disk's memory and to level the wear.
While hard disk drives are still more common, solid state drives are slowly gaining popularity. Commonly found in new laptops, SSDs have no moving devices, use less power, can take more of a beating, and provide much faster data access than hard drives in nearly all situations. For example, one of the fastest drives right now, the Crucial RealSSD C300, reads data at up to 355 megabytes per second, which is more than four times as fast as a regular notebook hard drive. On the downside, the capacities are still much lower than a similarly priced hard drive and the wear and tear may affect solid state drives slightly faster than hard disk drives. As with all new technologies, these teething problems are resolved as they are discovered and there is no doubt that the SSD will take over the role of the aging hard drive technology-it is only a question of when. For now, they are mostly found in high-end, enthusiast computers.
H.J. Berg is a freelance writer who regularly contributes to Fastest SSD - a data storage blog that focuses exclusively on high-end Solid State Drives. It covers the latest news in solid state storage technology and you will also find SSD reviews and helpful guides.
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