*HARD DRIVE

Read/Write Heads
A hard disk drive usually has one read/write head for each platter side, and these heads are connected, or ganged, on a single movement mechanism. The heads, therefore, move across the platters in unison.
Mechanically, read/write heads are simple. Each head is on an actuator arm that is spring-loaded to force the head into a platter. Few people realize that each platter actually is "squeezed" by the heads above and below it. If you could open a drive safely and lift the top head with your finger, the head would snap back into the platter when you released it. If you could pull down on one of the heads below a platter, the spring tension would cause it to snap back up into the platter when you released it.
Figure 1-2 shows a typical hard disk head-actuator assembly from a voice-coil drive.

Ribbon Cables
Ribbon cables are designed to be used in the installation of internal floppy and hard drives. MCC features a wide variety of high quality ribbon cables from standard floppy drive cables to the latest Ultra ATA IDE ribbon cables.
Our flat computer ribbon cables work with all IDE and EIDE devices such as hard disk drives (HDDs), CD-ROM drives, DVD-ROM drives, DVD Burners and CD-RW drives.

Hard Disk Platters
Larger hard drives that have 8-inch, 14-inch, or even larger platters are available, but these drives typically have not been associated with PC systems. Currently, the 3 1/2-inch drives are the most popular for desktop and some portable systems, whereas the 2 1/2-inch and smaller drives are very popular in portable or notebook systems. These little drives are fairly amazing, with current capacities of up to 1GB or more, and capacities of 20GB are expected by the year 2000. Imagine carrying a notebook computer around with a built-in 20GB drive. It will happen sooner than you think! Due to their small size, these drives are extremely rugged; they can withstand rough treatment that would have destroyed most desktop drives a few years ago.

Spindle Motors
The motor that spins the platters is called the spindle motor because it is connected to the spindle around which the platters revolve. Spindle motors in hard disks always are connected directly; no belts or gears are used. The motors must be free of noise and vibration; otherwise, they transmit to the platters a rumble that could disrupt reading and writing operations.

Head Actuator Mechanisms
Possibly more important than the heads themselves is the mechanical system that moves them: the head actuator. This mechanism moves the heads across the disk and positions them accurately above the desired cylinder. Many variations on head actuator mechanisms are in use, but all of them can be categorized as being one of two basic types:
• Stepper motor actuators
• Voice-coil actuators
The use of one or the other type of positioner has profound effects on a drive's performance and reliability. The effect is not limited to speed; it also includes accuracy, sensitivity to temperature, position, vibration, and overall reliability. To put it bluntly, a drive equipped with a stepper motor actuator is much less reliable (by a large factor) than a drive equipped with a voice-coil actuator.