Hybrid Hard Drive Definition

A hybrid hard drive is a hard disk drive (HDD) that also contains flash memory.

HDDs serve as the main storage device for most computers because of their outstanding combination of high capacity and high reliability along with a relatively small size and low cost. Their main disadvantage is a large power consumption (in comparison with semiconductor devices), which makes them one of the biggest drains on batteries on portable computers.

Flash memory, sometimes called flash RAM, is a type of semiconductor device that combines the important features of both memory, particularly high-speed access and low power consumption, with a main advantage of storage, which is the retention of data in the absence of a power supply. Its main disadvantage is that it is still much more costly on a per bit basis than other storage devices and media, such as HDDs and CDROMs.

Hybrid hard drives offer several important advantages as compared with conventional HDDs. One of these is a substantial reduction in power consumption. For example, Seagate Technology's first hybrid hard disk, the Momentus 5400 PSD, which was announced in June and which will contain a choice of 128MB (megabytes) and 256MB of flash memory, is claimed to cut HDD power consumption by up to 50 percent1.

This reduction occurs because the flash memory serves as a buffer for the HDD and thus the amount of time that the spindle motor, which rotates the platters, needs to be operated can be greatly reduced. Platters are thin disks that are coated on both sides with a high precision magnetic material and which are used in HDDs to store data. Thus, for example, when a user saves a document, the document is saved first to the flash memory instead of to the platters, and the contents of the flash memory are only transferred to the platters when the flash memory begins to become full.

A second advantage of hybrid hard drives is that they can allow computers to boot (i.e., start up) more quickly. This is because crucial portions of the operating system can be stored in the flash memory, thereby eliminating the need to wait for the HDD to start up and to copy those parts of the operating system from the HDD into conventional memory.

Some makers of personal computers will also likely embed commonly used application programs into the flash memory to allow them to launch more quickly.

Another advantage of hybrid hard drives is longer life expectancies. This is because of the large reduction in the amount of time that the motor and other electromechanical components are operating.

The main disadvantage of hybrid hard drives is that the cost is somewhat higher than for conventional HDDs because of the addition of the flash memory. However, this added cost is small relative to the benefits. Moreover, it will decrease as the costs of flash memory chips continue to come down.

The development of hybrid hard disks can be viewed as being part of a long-term trend towards the gradual replacement of hard disk drives with flash memory. It can also be seen as another small step towards the development of so-called green machines, which are computers that have much less adverse effects on the environment, including reduced power consumption and minimal use of toxic materials.

1The Momentus 5400 PSD (power saving drive) is a 2.5 inch hybrid drive that will spin at 5400RPM. Perpendicular recording will allow capacities of up to 160GB. Shipment is scheduled for the first quarter of 2007. The Scotts Valley, California-based Seagate is one of the world's largest suppliers of HDDs.

Created June 8, 2006.
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