Hard Drives (continued...)

PreComp, Landing Zone and Zone Bit Recording
Landing Zone - The read/write heads on a hard drive have to be parked. When the drive is spinning, it creates a cushion of air above its surface. The heads actually float on this cushion of air. When the computer is turned off, leaving the heads over top of cylinders containing information could result in head crashes and damaged sectors. So, the heads have to be moved over a portion of the disk that is not used to hold data (usually the last inside track of the drive), before power to the drive is shut down. This area is called the landing zone. Parking the heads used to involve a small program that would move them overtop of an unused track.

Write Precompensation - Early hard drives (and floppy drives) have a consistent number of sectors per track. This means that, although the sectors still contain 512 bytes, the physical size of each sector gets smaller towards the center of the platter. As the sectors become smaller and smaller, with the same number of bytes being packed into the sector, the ability for the media to hold that data decreases. For hard drives, the read/write heads had to adjust the way they wrote the data, so that the information didn't get pushed out of the smaller area. The most popular way was called write precompensation. The current in the heads would be increased when writing data past a certain pre-defined (in your BIOS setup) track number.

Zone Bit Recording - Today's drives don't need to worry about precompensation because they don't have a consistent number of sectors on each track. Zone Bit Recording is a method by which the number of sectors per track decreases as you reach the center of the disk. There are a lot more sectors on the outside tracks than there are on the inside tracks. The drive's BIOS and controller can translate the information into a form that the computer's BIOS and operating system can understand. To put it simply, it lies.

So, enter your system's setup program and check out the settings for the fixed disk. You may see Lzone and Precomp. You don't need an entry under Landing Zone because today's disks park themselves automatically. And thanks to Zone Bit Recording, you can enter 0 under Write Precompensation (or 65535) to indicate that it's not required. With some new drives, you may also see the word 'auto' here. This means that you don't have to configure the hard drive in setup, it's configured automatically during the boot-up process.

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