Page 342 - FUNDAMENTALS OF COMPUTER

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342 Fundamentals of Computers NPP

EPROM are very economical and conve- BZH$m Cn`moJ AZwg§YmZ d {dH$mg Ho$ H$m`© _| hmoVm
nient to use in design and development. In h¡ Ÿ& Š`m|{H$ Eogr OJh na àmoJ«m_ H$mo Om§MH$a ~ma-~ma
research a program may need several modifi- ~XbZm hmoVm h¡ Ÿ& AV… EH$ hr {Mn go H$m_ Mb OmVm
cations. Thus, a single EPROM can be used to
test the program. The problem with this type is h¡ Ÿ& bo{H$Z Bg àH$ma H$s EPROM _| EH$ g_ñ`m `h
that the whole program is erased, not one or hmoVr h¡ {H$ {H$gr EH$ `m Hw$N> bmB©Zm| H$mo MwZH$a Zht
few memory locations. hQ>m`m Om gH$Vm Ÿ& g§nyU© àmoJ«m_ H$mo hr hQ>mZm n‹S>Vm h¡&
EEPROM (E PROM) Electrically Erasable BbopŠQ´>H$br BaoOo~b PROM (EEPROM)
2
PROM
Electrical pulses are used to erase the con- `o ^r \o$ŠQ´>r go Imbr AmVr h¡ Am¡a Bg_| ^r
tents of the chip. This chip is also known as EEPROM àmoJ«m_a Ûmam àmoJ«m_ {bIm OmVm h¡Ÿ& na§Vw
EAPROM (Electrically Alterable PROM) be- BgH$s OmZH$mar H$mo {dÚwV H$s ghm`Vm go hQ>m`m Om
cause we can select one or more locations gH$Vm h¡ & BgHo$ {bE gm_mÝ` dmoëQ>oO go ~hþV A{YH$
which need alteration. No need to erase the
whole program. The voltages used to erase n[aUm_ H$m dmoëQ>oO XoZm hmoVm h¡Ÿ& Hw$N> hr {_{bgoH§$S> _|
the contents of EEPROM are much higher than OmZH$mar hQ> OmVr h¡Ÿ& BgH$m EH$ Am¡a \$m`Xm `h h¡
the normal operating voltages. Few millisec- {H$ {H$gr EH$ _o_moar ES´>og H$mo MwZH$a Cgo ~Xbm Om
onds are required to erase the contents of a gH$Vm h¡Ÿ& Bg{bE Bgo EAPROM (BbopŠQ´>H$br
chip. For erasing purpose one extra circuit is AëQ>ao~b àmo_) ^r H$hVo h¢Ÿ& bo{H$Z àmoJ«m_ H$mo hQ>mZo
required. Ho$ {bE EH$ A{V[aŠV n[anW H$s Amdí`H$Vm hmoVr h¡&

4.4 Floppy Disk 4.4 âbm°nr {S>ñH$
Floppy disks are “thin and flexible”. There- âbm°nr {S>ñH$ ""nVbr d bMrbr'' hmoVr h¢, Bg{bE
fore these are called floppy disks or diskettes. ""âbm°nr'' H$hbmVr h¡Ÿ& BÝh| {S>ñH$sQ> ^r H$hVo h¢Ÿ& `o
Floppy disks are made up of plastic sheet called _mBba Zm_H$ ßbmpñQ>H$ go d¥ËVmH$ma erQ> Ho$ ê$n _| ~Zr
Mylar. The surface is coated with an Iron oxide
material. Iron oxide is a magnetic material. The hmoVr h¡ Ÿ& BgH$s gVh na Am`aZ Am°ŠgmB©S> H$s naV
sheet is covered in a protective cover made of M‹T>m Xr OmVr h¡ Omo {H$ EH$ Mw§~H$s` nXmW© h¡Ÿ& A~ Bgo
plastic. Floppy is a removable disk. That means, ßbmpñQ>H$ go ~Zo dJm©H$ma àmoQ>opŠQ>d H$da _| aI {X`m
it is inserted into the computer when needed, OmVm h¡Ÿ& Bgo AmgmZr go H$åß`yQ>a _| àdoe H$adm`m Om
and can be removed after the need is over. The
access time of floppy disk is of the order of ms gH$Vm h¡ VWm dmng {ZH$mbm Om gH$Vm h¡& BgH$m
(milliseconds). EŠgog g_` {_{bgoH§$S> _| hmoVm h¡&

Storage organisation of floppy disk âbm°nr _| ñQ>moaoO g§aMZm
The magnetic surface is divided into con- g§nyU© Mw§~H$s` gVh H$mo d¥ÎmmH$ma nWm| _| {d^m{OV
centric circles, called track. Each track is di-
vided into logical areas called sectors. The shape H$a XoVo h¡ Omo Q´>¡H$ H$hbmVo h¢Ÿ& àË`oH$ Q´>oH$ H$mo goŠQ>am|
of sector may be considered as arc of the Circle _| {d^m{OV H$a XoVo h¢Ÿ& Q´>oH$ d goŠQ>a XmoZm| Vm{H©$H$ joÌ
(track). Track is also a logical area on the sur- hmoVo h¢Ÿ& BZ_| (0, 1) Ho$ ê$n _| OmZH$mar g§J«{hV hmoVr
face. The information is stored in the form of
bits (0,1). small spots are magnetised in clock- h¡Ÿ& N>moQ>o-N>moQ>o ñnm°Q>m| na K‹S>r H$s {Xem `m BgHo$ {dnarV