7 - Hard Disk

How Hard Disks Work by Marshall Brain Cassette Tape vs. Hard Disk Let's look at the big differences between cassette tapes and hard disks: • The agnetic recording aterial on a cassette tape is coated onto a thin plastic strip. !n a hard disk" the agnetic recording aterial is layered onto a high# precision al$in$ or glass disk. The hard#disk platter is then polished to irror#type soothness. • %ith a tape" yo$ have to fast#forward or reverse to get to any partic$lar point on the tape. This can take several in$tes with a long tape. &n a hard disk" yo$ can ove to any point on the s$rface of the disk alost instantly. • !n a cassette#tape deck" the readwrite head to$ches the tape directly. !n a hard disk" the readwrite head (flies( over the disk" never act$ally to$ching it. • The tape in a cassette#tape deck oves over the head at abo$t ) inches *abo$t +.,- c per second. / hard#disk platter can spin $nderneath its head at speeds $p to 0",,, inches per second *abo$t 12, ph or )2) kph3 • The inforation on a hard disk is stored in e4treely sall agnetic doains copared to a cassette tape's. The si5e of these doains is ade possible by the precision of the platter and the speed of the edi$. 1 6early every desktop cop$ter and server in $se today contains one or ore hard#disk drives. 7very ainfrae and s$percop$ter is norally connected to h$ndreds of the. 8o$ can even find 9C#type devices and cacorders that $se hard disks instead of tape. These billions of hard disks do one thing well ## they store changing digital inforation in a relatively peranent for. They give cop$ters the ability to reeber things when the power goes o$t. !n this article" we'll take apart a hard disk so that yo$ can see what's inside" and also disc$ss how they organi5e the gigabytes of inforation they hold in files3 Hard Disk Basics Hard disks were invented in the 1;+,s. They started as large disks $p to ), inches in diaeter holding <$st a few egabytes. They were originally called (fi4ed disks( or (%inchesters( *a code nae $sed for a pop$lar !BM prod$ct. They later becae known as (hard disks( to disting$ish the fro ( floppy disks.( Hard disks have a hard platter that holds the agnetic edi$" as opposed to the fle4ible plastic fil fo$nd in tapes and floppies. /t the siplest level" a h ard disk is not that dif ferent fro a cassette tape. Both hard disks and cassette tapes $se the sae magnetic recording techni=$es described in How Tape ecorders %ork. Hard disks and cassette tapes also share the a<or benefits of agnetic storage ## the agnetic edi$ can be easily erased and rewritten" and it will (reeber( the agnetic fl$4 patterns stored onto the edi$ for any years. !n the ne4t section" we'll talk abo$t the ain differences between cassette tapes and hard disks.

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7 - Hard Disk