Page 353 - FUNDAMENTALS OF COMPUTER

NPP

NPP Memory 353

contents of CD-ROM, a low power LASER beam S>mbr OmVr h¡& {nQ> go VWm b|S> go namd{V©V àH$me H$s
is made incident on the CD surface. The inten-
sity of reflected light from a pit is different Vrd«Vm AbJ-AbJ hmoVr h¡Ÿ& Bgr Vrd«Vm H$mo EH$ \$moQ>mo
from the intensity of reflected light from land. {S>Q>oŠQ>a S>m`moS> {dÚwV Va§Jm| _| ~XbH$a 1 VWm 0 H$s
This is how 0 and 1 are distinguished. A pho- nhMmZ H$aVm h¡Ÿ& coOa ~r_ H$s Vrd«Vm cJ^J 5 mw
todetector is used to convert the light pulse
into electrical pulse. The intensity of laser for hmoVr h¡Ÿ&
reading is about 5 mw.
Storage Structure of CD-ROM CD-ROM H$s g§J«hU g§aMZm
The information is stored on a single con- EH$ hr gnubmH$ma nW na gmar OmZH$mar g§J«{hV
tinuous spiral as shown below: hmoVr h¡ O¡gm {H$ ZrMo {MÌ ‘| Xem©¶m J¶m h¡…

Spiral groove
Block
The spiral track is divided into blocks. Each gnubmH$ma nW ^r ãbm°H$m| _| ~Q>m hmoVm h¡ Ÿ& àË`oH$
block contains about 2 KB of data. The disk ãbm°H$ _| bJ^J 2 KB H$m S>mQ>m AmVm h¡ Ÿ& {S>ñH$
rotates with a variable speed to provide the n[ad{V©V J{V go Ky_Vr ahVr h¡ Vm{H$ hoS> pñWa J{V go
constant linear speed to the head.
{bI-n‹T> gHo$Ÿ&
Advantages of CD-ROM: bm^:
1. High Storage Capacity. 1. CÀM j_VmŸ&
2. Low cost because of mass production. 2. H$_ bmJVŸ&
3. Removable from Computer. 3. AmgmZr go bJmB© {ZH$mbr Om gH$Vr h¡Ÿ&
4. Less chances of wear and tear. 4. Qy>Q>-\y$Q> H$s H$_ g§^mdZmŸ&
Disadvantages of CD-ROM: hm{Z`m±:
1. High Access time. (Slower) 1. CÀM EŠgog g_` (Yr_r)Ÿ&
2. Not reprogrammable. 2. {\$a go àmoJ«m_ Zht S>mb gH$VoŸ&
3. Error bits are present. 3. Ìw{Q> {~Q>| nmB© OmVr h¢Ÿ&
Uses of CD-ROM: Cn`moJ:
1. For distribution of software; compiler, op- 1. gm°âQ>do`a {dVaU hoVwŸ; O¡go H§$nmB©ca, Am°naoqQ>J
erating system, packages etc. {gñQ>_, n¡Ho$O Am{XŸ&