what is a hard disk drive

7/31/2019 What is a Hard Disk Drive

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What Is a Hard Disk Drive?

Beginners Guide


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What Is a Hard Disk Drive? Beginners

Guide

Your Hard Disk or sometimes called a Hard Drive,is the main storage space inside your PC. It is apermanent storage component unlike the RAM

(Random Access Memory). It is possible for yourcomputer to function without a hard disk,however it would be basically useless to you asyou would not be able to use an Operating

system or have any programs to use. Unless youhad another form of mass storage device such asan SSD (Solid State Drive).


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Hard disks use circular hard platters to storedata on. They are in pristine condition with amirror like finish to them. These platters arelocked away inside a steel casing as unclean

air can easily ruin a hard disk. This is why youshould never remove the casing from the harddisk, it is very unlikely you will be able to put itback together as a working component. Even a

small amount of dust can render a hard diskplatter useless.


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Below you can see a labelled diagram of a harddisk. The model is a SCSI (Small ComputerScientific Interface) You can see the hard platterson top of each other with a set of arms whichhold the read/write head. The speed of the arm is

truly amazing as well as the accuracy of the headwhich can read and write to perfection on aplatter which is rotating around 7200RPM. Thehard disk looks a very simple idea and probably

is, however a lot goes on before the simplewriting to the disk its self.


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How does the hard disk store data?

On each of the platters there is a thin layer ofmagnetic film. Data storage on hard disks is verysimilar to that of a cassette tape. Data is stored inmany 1's and 0's stored in different directions on

the magnetic film by using a very fine oxide.These binary digits are arranged in different waysto represent different characters. When these areread back by the head the data is retrieved and

processed. because no physical contact with theplatters is made the disk can be re-written timeand time again without damage to the disk or itsplatters.


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File Systems

A file system is the way in which your computer stores dataon the hard disk. The most common file systems are FAT16for older computers, FAT32 and NTFS. FAT standsfor File Allocation Table. NTFS stands forNT File System.Both have advantages and disadvantages. FAT16 was a verylimited file system in the way that it would store data veryin-efficiently, every file would take up a minimum of 32Kbin space as this was the minimum cluster size in a FAT16system. Also it was only capable of using hard disks up to2Gb in size. FAT32 solved this problem by reducing thecluster size to 4kb which saved a lot of wasted space and

also allowed disk sizes up to 2 Terra bytes. NTFS is believedto be a far greater file systems than any of the FAT's. Thecluster sizes can be altered to anything as low as 512byteswhich means almost no wasted space on the hard disk. Themaximum disk size is a unbelievable 256 Terra bytes, which

is very big !!!. NTFS also has added security for file loss.


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Measuring the Speed of a Hard Disk

There are various ways of measuring the speed of thehard disk. The main ones are the maximum datatransfer rate, the spindle rotation speed and the seektime.

Maximum Transfer Rate - This is the highest amountof data that can be transferred per second. Commonforms of hard disks come with an ATA format. thespeed rating of an ATA100 disk would be 100Mb/s.Likewise a ATA66 disk would be able to transfer a

maximum of 66Mb/s. Past the older ATA standard justmentioned comes the newer S-ATA standard (serial-ATA). S-ATA 1.0 transfers at a max rate of 1.5Gb/s S-ATA2.0 transfers at a max rate of 3Gb/s and S-ATA 3.0 cantranfer data a maximum rate of 6Gb/s


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Spindle Rotation Speed - The rotation speed of the disk

really is the basis of the other two factors of hard diskspeed. The faster the rotation speed, the more datacan be written per second and the quicker it is to findthe correct data on the platter. A Common speed is7200RPM (revolutions per minute)

Seek Time - The seek time of a hard disk is the averagetime it takes for the disk to find the data you need onthe platters. A fast spinning, highly accurate andresponsive disk will have a shorter seek time and will

perform much better, especially when the data isscattered around the disk. Seek time is measured inmilliseconds or ms.


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Disk Fragmentation

All versions of Windows come with a diskdefragmenter. But what exactly is fragmentation? Asyou use your computer daily files get written anddeleted constantly from the disk, either by yourself or

by the operating system creating and removingtemporary files. This process leave the disk in no sortof order and when new file are written to the disk theystart to get written in the gaps on the disk. The factthat single files are written in different parts of the disk

means that the disk has to go round the disk readingdifferent parts instead of just streaming the datastraight off the disk. This is called Fragmentation. Thedefrag program within windows sorts out the files intoorder again to make the disk perform faster.


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Connection Types There are currently 4 connections for a hard disk. IDE (or ATA) SCSI,

Serial ATA and USB. The most common is the IDE interface. Thisprovides an 80 pin connection to most standard motherboards andyou can't normally go wrong buying an IDE drive for your machine.SCSI connections often require extra hardware unless its built intoyour motherboard. SCSI hard disks are often faster but moreexpensive than there IDE counterparts. Serial ATA does away withparallel data transfer which has its problem of large wires andelectrical interference. The Serial ATA standard is more reliable anduses smaller un-obtrusive wires. Smaller wires also means better airflow for your case. Serial ATA hard drives can also work faster at ahigher data throughput giving your overall system a speed boost.The final connection type is the USB (Universal Serial Bus)connection. This connection is used for connecting external harddrives to your machine. While not as fast as the internal Serial ATAconnection, it has the usefulness of being able to disconnect easilyfrom the PC and taken to another PC and plugged straight in.Perfect for storing a lot of files to be used on multiple computers.


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IDE


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SCSI


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Serial ATA


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USB


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