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TIHE Encyclopedia

Hard Disk by Marshall Brain

There are currently 3 connections for a hard disk. IDE (or ATA) SCSI and Serial ATA. The most common is the IDE interface. This provides an 80 pin connection to most standard motherboards and you can't normally go wrong buying an IDE drive for your machine. SCSI connections often require extra hardware unless its built into your motherboard. SCSI hard disks are often faster but more expensive than there IDE counterparts. The final type is the newest type. Serial ATA does away with parallel data transfer which has its problem of large wires and electrical interference. The Serial ATA standard is more reliable and uses smaller un-obtrusive wires. Smaller wires also means better air flow for your case.

How does data Store?

On a harddisk, data is stored in the magnetic coating of the disk. The so called head, held by an actor arm, is used to write and read data. This disk rotates with a constant turn time, measured in revolutions per minute (rpm). Data is organized on a disk in cylinders, tracks and sectors. Cylinders are concentric tracks on the surface of the disk. A track is divided into sectors. A harddisk has a head on each side of a disk. Nowadays, the actuator arm is moved by a servo-motor (not a step-motor which needs more time while swinging in after moving over the desired track). All harddisks have reserved sectors, which are used automatically by the drive logic if there is a defect in the media.

Diagram 1

File Systems

A file system is the way in which your computer stores data on the hard disk. The most common file systems are FAT16 for older computers, FAT32 and NTFS. FAT stands for File Allocation Table. NTFS stands for NT File System. Both have advantages and disadvantages. FAT16 was a very limited file system in the way that it would store data very in-efficiently, every file would take up a minimum of 32Kb in space as this was the minimum cluster size in a FAT16 system. Also it was only capable of using hard disks upto 2Gb in size. FAT32 solved this problem by reducing the cluster size to 4kb which saved a lot of wasted space and also allowed disk sizes up to 2 Terra bytes. NTFS is believed to be a far greater file systems than any of the FAT's. The cluster sizes can be altered to anything as low as 512bytes which means almost no wasted space on the hard disk. The maximum disk size is a unbelievable 18.5 x 10นบ bytes, which is very big !!!. NTFS also has added security for file loss.

Speed of Drive

The speed of a drive is measured in milliseconds so 10ms is faster than 12ms the RPM (revs per minute) is also important for speed. The higher number of RPM's the better, also any cache if possible, all of this improves the speed of the drive under some circumstances your hard drive does get some serious hammering so its very important to pick the right one.

Diagram 2
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