An Introduction to the
Solid State Hard Drive

The solid state hard drive is not really a "hard drive" in the original meaning of the word because it has no moving parts and the data is not stored on magnetic platter. It is merely called a hard drive because the term has become synomyous for general purpose storage devices.

Many solid state hard drives have an external form factor which allow it to be used in place of the traditional hard disk drive. Though a solid state drive costs more per gigabyte, it has many advantages over the original hard drive.

Another name for the solid state hard drive is the solid state disk (SSD). No matter what the name, the key distinction is that the SSD stores its data in a semiconductor material such as NAND flash or SDRAM.

Advantages

Not having any moving parts, means that the solid state drive has fewer reasons to break. This translates into increased reliability. By not being a mechanical device, it has advantages such as low power consumption, survivability in hostile environments and quicker access times.

An SSD can use either non-volatile memory such as flash, or volatile memory such as SDRAM. When volatile RAM is used, the vendor puts the disk into a rack mountable case with a battery to preserve power in the event of an unexpected power outage. These silicon based disks are mostly used in military, corporate computer room, and industrial environments.

Access times for the solid state hard drive can be up to 500 times faster than for the hard disk. In contrast, the hard disk is much slower because it has to go through the motions of moving the heads and waiting for the platters to rotate to the desired position before data can even be read. Improving disk access times is very beneficial when an application uses lots of small files.

Some environments are too hostile for a drive with a spinning platter to survive for long. The mechanical drive is too susceptible to damage from moisture, dust, vibrations, shock, and extreme temperatures. In sharp contrast, the solid state hard drive will survive more easily in all of these environments.

Disadvantages

But the solid state drive is not immune to problems, foremost of which is that flash memory has a limited number of read/write cycles.

Another problem for NAND flash has to do with the large block sizes. The block sizes of NAND flash disks can easily be 64KB or larger. The issue, for writes, is that the entire block needs to be written, even if only one byte has to change. It gets even worse because the entire block needs to be erased before the new data can be written.

Understandably, this creates huge performance pot holes when large numbers of tiny files are being updated. Because of this, NAND flash works best when large blocks of sequential writes make up the bulk of the I/O load.

Hybrid Drive

The hybrid drive is a hard disk that incorporates some of the benefits of the solid state drive. The hybrid drive has a large amount of flash memory incorporated into the hard disc electronics. The flash is used as a cache to speed up disk access. Windows Vista provides a feature called ReadyDrive which is designed to take advantage of the hybrid drive. ReadyDrive will help the PC to boot faster and reduce power consumption.

The continued decline in prices of flash and SDRAM will make solid state hard drives more attractive to the consumer market. They are already being used in some high-end portable computers.

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