Another advancement in actuator control will be the use of active damping. When the actuator is stopped over a track, it has a tendency to vibrate. Active damping uses the actuator motor to suppress the vibration, allowing the head to settle more quickly and accurately. Essentially, the control processor implements the motor to slow down the actuator in the direction of each vibration cycle.
The 3.5-in. drive market is dominated by a number of large companies, including Fujitsu, Hitachi America Ltd., IBM, Maxtor, Seagate Technology, Toshiba Corp., and Western Digital. Some, such as Maxtor, work exclusively in the 3.5-in. space. This type of drive addresses a large space from consumer applications through enterprise uses. Single drives are found in desktop PCs and embedded applications, and multiple drives are seen in various redundant-array-of-inexpensive-disks (RAID) configurations (see "An Introduction To RAID," p. 110).
Interfaces for hard-disk drives span an equally wide range. They vary from those that support low-end parallel ATA ports for two drives per controller, through high-end interfaces like Fibre Channel that handle up to 125 devices per controller.
One area in which 3.5-in. drives aren't dominant is laptops and embedded applications where size is critical. Smaller drives come into play here. For example, 2.5-in. drives are the most popular on regular laptops. Furthermore, while 1.8-in. drives are making some inroads here, these even smaller drives are finding a better home in embedded applications where space, but not capacity, is critical.
Other specialized drives exist with different form factors, like IBM's MicroDrive. This has a CompactFlash form factor, letting it be used in a variety of portable applications including digital cameras. The 1-Gbyte version is very popular with photography professionals, because high-end digital cameras generate multimegabit image files.
Like 3.5-in. disk drives, capacity and performance is increasing for these smaller form-factor drives. But, they're still far short of the 3.5-in. drives in terms of capacity and performance. The small disk sizes simply don't have the area necessary to compete with the 3.5-in. drives.
Interestingly, 2.5-in. drives are showing up in rack-mount RAID arrays. The reason is that more drives can fit into the same amount of space, providing better redundancy and higher performance due to the parallel operation of more disks in comparison to a similar 3.5-in. solution. Still, most installations have sufficient space for 3.5-in. RAID arrays, which have higher disk and system capacities.
In all likelihood, the yearly doubling of hard-disk capacity should continue with the low-end capacity reaching 20 Gbytes. The Serial ATA interface may become a factor in late 2001, but parallel ATA, SCSI, and Fibre Channel will support the bulk of the drives shipped in 2001.