Page 348 - FUNDAMENTALS OF COMPUTER

NPP

348 Fundamentals of Computers NPP

Head
Spindle

Al disk

Head
Assembly Iron Oxide
Coating

Rotation of
spindle
Direction of
Head movement
When the spindle rotates, all the plates O¡go hr pñnÝS>b Ky_Vm h¡, gmar ßboQ>| ^r BgHo$ gmW
also rotate. The head assembly can move to- Ky_Zo bJVr h¢Ÿ& hoS> H$m Pw§S> pñn¨S>b Ho$ nmg Am gH$Vm
wards and away from the spindle. The Heads
are not in direct physical contact of the surface. h¡ `m Cggo Xya Om gH$Vm h¡Ÿ& hoS> grYo-grYo ßboQ> H$s
Two heads are needed for one platter. Each gVh H$mo ñne© Zht H$aVoŸ& do Hw$N> µm D$na hmoVo h¢ Ÿ&
surface is divided into tracks and sectors. The àË`oH$ ßboQ> H$s XmoZm| gVhm| Ho$ {bE Xmo hoS> Amdí`H$ hmoVo
heads can move radially and the spindle can h¢ Ÿ& àË`oH$ gVh Q´>oH$m| VWm goŠQ>am| _| ~§Q>r hmoVr h¡ Ÿ&
rotate. Thus, track to track movement of head
assembly is random. But if sectors can be read Q´>oH$ go Q´>oH$ H$s J{V a|S>_ hmoVr h¡ Ÿ& bo{H$Z goŠQ>a H$mo
serially. The time taken by head to move from loUr _| hr n‹T>m Om gH$Vm h¡ Ÿ& EH$ Q´>oH$ go Xygao Q´>oH$
one track to another track is called seek time. na OmZo _| bJo g_` H$mo grH$ Q>mB©_ H$hVo h¢ Ÿ& {H$gr
The time elapsed in waiting for a desired sector Mmho JE goŠQ>a H$mo n‹T>Zo Ho$ {bE Omo g_` bJVm h¡ Cgo
is called rotational latency time. The total of
these two is called access time. Access time is amoQ>oeZb boQ>|gr Q>mB©_ H$hVo h¢ Ÿ& grH$ Q>mB©_ d boQ>|gr
of the order of ms. All heads move simulta- Q>mB©_ Ho$ `moJ H$mo EŠgog Q>mB©_ H$hVo h¢ Ÿ& My±{H$ gmao hoS>
neously. Therefore each head happens to be on EH$ gmW J{V H$aVo h¢ Bg{bE gmao hoS> {H$gr {XE JE
a track of same radius. The group of all such jU na g_mZ {ÌÁ`m dmbo Q´>oH$m| na hr hm|JoŸ& gmao Q´>oH$m|
tracks is called a cylinder. The information is
read from or written into a cylinder. The collec- Ho$ Cg g_yh H$mo {OZH$s {ÌÁ`m g_mZ h¢, {gb|S>a H$hVo
tion of all disks and the spindle is called disk h¢ Ÿ& Bgr {gb|S>a na OmZH$mar {bIr OmVr h¡ `m Bgr
pack. The disk pack and head assembly are go n‹T>r OmVr h¡ Ÿ& {S>ñH$ d pñnÝS>b H$mo {_bmH$a {S>ñH$
vacuum sealed. The speed of hard disk is very noH$ H$hVo h¢Ÿ& {S>ñH$ noH$ d hoS> Agoå~br XmoZm| H$mo {Zdm©V