|  The Read/Write Heads: The read/write heads read and write data to the platters. There is typically one head per platter side, and each head is attached to a single actuator shaft so that all the heads move in unison. When one head is over a track, all the other heads are at the same location over their respective surfaces. Typically, only one of the heads is active at a time, i.e., reading or writing data. When not in use, the heads rest on the stationary platters, but when in motion the spinning of the platters create air pressure that lifts the heads off the platters. The space between the platter and the head is so minute that even one dust particle or a fingerprint could disable the spin. This necessitates that hard drive assembly be done in a clean room. The Head Actuator: All the heads are attached to a single head actuator, or actuator arm, that moves the heads around the platters. Older hard drives used a stepper motor actuator, which moved the heads based on a motor reacting to stepper pulses. Each pulse moved the actuator over the platters in predefined steps. Stepper motor actuators are not used in modern drives because they are prone to alignment problems and are highly sensitive to heat. Modern hard drives use a voice coil actuator, which controls the movement of a coil toward or away from a permanent magnet based on the amount of current flowing through it. Types of Hard Drives IDE Drives: Integrated Drive Electronics (IDE) systems put most of the electronics on the drive itself. The encoding and decoding and the control signals are done on the circuit board under the drive. The adapter card just relays the signals from the drive to the computer. In essence, the drive is an independent thing from the computer and it takes care of itself. IDE Drives are today's standard and are the default drive on almost all modern computers. But, with the need for speed that many people have, the IDE drive is sometimes passed over for a faster interface. | SCSI Drives: SCSI (pronounced "skuzzy") stands for Small Computer Systems Interface. SCSI drives are independent. Their bus is completely separate from the usual buses, such as PCI or ISA. They also do not rely on the BIOS to be able to talk to the computer. They are completely independent. When the computer boots, it checks for additional hardware ROMs. As it does this, it finds your SCSI adapter card, if you have one. It gets no details as to what is attached to the adapter. You can connect as many as seven SCSI devices to the adapter, without the computer's knowledge. The adapter keeps track of the data flow across the SCSI bus. Each device gets its own SCSI address. Each device can talk with the other SCSI devices across the bus, all independent from the computer.The SCSI interface certainly speeds up the computer, but many problems come with the added speed. |
| There are no set standards for SCSI; there is the original SCSI and the newer SCSI-2. These two sometimes have a hard time talking to each other in your computer. Also, many companies have developed proprietary SCSI standards. A drive like this may not be able to talk with a SCSI device of another make. SCSI hardware requires drivers unique to the operating system you are using and your special hardware combination. Each device requires its own ID number, with the end of the chain being set to be the end device. For these reasons, configuring SCSI is considered hard. EIDE Drives: EIDE is simply Enhanced IDE. It takes out some of the limitations of the original IDE interface. You can put as many as four devices on one controller. EIDE also allows non-disk devices to be used, such as CD-ROMS. The original IDE allowed only hard drives. EIDE allows the use of much higher capacity drives, up to 9 GB or so. It has a transfer rate of around 11.1 MB per second, much faster than IDE, and it also allows you to take advantage of the PCI interface from your new video card.
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