of Win95), FAT32 (used by later versions of Win95 and IBM's OS/2) New Technology File System (NTFS, used only on Windows NT), and High Performance File System (HPFS, also used alternately by 05/2 and Windows NT)

of Win95), FAT32 (used by later versions of Win95 and IBM's OS/2) New Technology File System (NTFS, used only on Windows NT), and High Performance File System (HPFS, also used alternately by 05/2 and Windows NT).

The FAT, FAT32, and NTFS file systems rely upon clusters as an integral part of data storage. A cluster is the smallest allocation unit in these three file systems. Tne table is much like a road map that represents whether each duster of a disk is free or allocated to a file.

~lpes Of Drives. Although an hard drives work in a similar fashion, drive manufacturers developed different designs as their knowledge of hard drive technology grew. These different desi~s resulted in improved performance, and some designs also proved to be more reliable and better choices for various computer systems. Hard drives are categorized by the type of interface circuit they use to communicate to the motherboard, the circuit board that makes up the foundation of the computer.

Think of an interface as a type of electronic connection between a computer device and the computer's circuits.

The Integrated Drive Electronics (IDE) hard drive, first developed by Compaq Computer Corp. in 1986, is the most common type. This type of drive is also called Advanced Technology Attachment (ATA). IDE is a disk interface standard based upon the

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Head actuator. Controls the read/write heads.

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IBM FC ISA (Integrated Systems Architecture) 16-bit bus, but it also is used on other personal computers. The bus is a part of the computer's internal communication system that controls how much data can travel from the hard drive to the motherboard at one time. The IDE specification deals with the power usage and data signal interfaces between the motherboard and the integrated disk controller and drive.

The IDE bus only can support two hard drive devices in a computer. One device is called the master drive; the other is called the slave. To ensure that IDE drives made by different manufacturers will work in any computer, hard drive manufacturers embed a translator for the proper IDE interface or controller so the hard drive can communicate with the motherboard. IDE controllers are actually direct connections to the ISA bus.

An improved version of the IDE hard drive is the Extended Integrated Drive Electronics (EIDE) drive. It can process faster data rates and work more efficiently with the 32-bit bus found in Pentium computers. It also can provide enhanced performance in some drives that use the Direct Memory Access (DMA) feature. EIDE was coined by hard drive manufacturer Western Digital Corp. in about 1994, and the standard is also referred to as Fast ATA-2.

A third hard drive type, the Small Computer System Interface (SCSI, pronounced scuz-zee), was originally called SASI

Circuit board (logic board). Receives commands from the

hard drive controller and translates them in order to move the head actuator, which moves the readlwrite head across the platters.

(Shugart Associates System Interface) when it was first introduced as a propriet~uy device in certain computers. Its superior performance quickly made it an indus5i standard. The original standard is now called SCSI-1 to disfinguish it from SCSI-2 and SCSI-3, which indude specifications of Wide SCSI (a Ibbit bus) and Fast SCSI, which transfers data at 10MB per second. The SCSI drive interface can control more than two hard drives and other peripherals such as scanners and backup drives.

Computers that use the SCSI interface can have many SCSI drives daisy chained to other devices to provide almost unlimited storage capacity. (In a daisy chain setup, a set of hardware components are connected in a series, where the first component connects to the computer, the second component connects to the second, and so on.)

All this hard drive jargon can confuse the computing beginner. Even if you don't know all the ins and outs of hard drive types when Shopping for a computer, you must know the most important performance factor to consider in a hard drive: its seek time. Seek time is the time it takes for a hard drive's read/write head to access a particular spot on a platter to find data. For a hard drive to start to read or write to a given location, its read/wnte head must be positioned radially over the right track and rotationally over the start of the right sector.

Radial motion causes most of the intermittent noise heard during drive activity. Hard drives usually have one read/write head for each disk surface and all these heads move together. Tne set of locations that are accessible with the heads in a given radial position comprises the cylinder. Thus, the seek time is how long it takes the heads to move to a different cylinder to find the requested data.

High speed drives have an access time of

Spindle. spins the platters and is run by a motor.

28 milliseconds (ms, one-thousandth of a second) or less, and low-speed drives run at 65ms or faster. The higher speed drives also transfer data faster than slower units.

Read/write heads. Move across the platters to write data to and read data from the platters.

Platters. The aluminum alloy disks upon which data is stored in a hard drive

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