Page 340 - FUNDAMENTALS OF COMPUTER

NPP

340 Fundamentals of Computers NPP

ROM ROM
As the name implies the contents of ROM O¡gm {H$ Zm_ go hr ñnï> h¡, BgHo$ A§Xa H$s
memory can be read only (as long as it is in the OmZH$mar {g\©$ n‹T>r Om gH$Vr h¡Ÿ (O~ VH$ ¶h H$å߶yQ>a
computer system). The program written in the
ROM cannot be modified by the user or pro- {gñQ>‘ Ho$ AÝXa h¡)& BgHo$ A§Xa Omo àmoJ«m_ hmoVo h¢,
grammer. ROM is also available in the form of CZH$mo Cn`moJH$Vm© ¶m àmoJ«m‘a n[ad{V©V Zht H$a gH$VmŸ&
semiconductor chip. It is also organised as a `o ^r AY©MmbH$ H$s {Mn (IC) Ho$ ê$n _| CnbãY h¡Ÿ&
group of equal-sized addressable registers.
Address of a particular register is applied to a Bg_| ^r g_mZ AmH$ma Ho$ ES´>ogo~b a{OñQ>a hmoVo h¢ &
particular ROM chip, then a control signal {H$gr {deof a{OñQ>a H$mo n‹T>Zo hoVw BgH$m ES´>og àXmZ
“read” is provided by the CPU to read the H$aZm hmoVm h¡ Ÿ& gmW hr EH$ {Z`§ÌU {g¾b ""arS>'' ^r
contents of that register. The registers in the àXmZ H$aZm hmoVm h¡ Ÿ& amo_ Ho$ a{OñQ>a ^r aoÊS>_ àH$ma
ROM can also be “randomly accessed”. Thus,
ROM is also a random access memory. ROM is go EŠgog hmoVo h¢Ÿ& Bg àH$ma, ¶h EH$ a¡ÊS>‘ E³gog
used to hold some permanent programs and ‘o‘moar ^r h¡& Bg_| Hw$N> ñWm`r àmoJ«m_ d pñWa S>mQ>m aIo
some fixed data. e.g. monitor program of a OmVo h¢Ÿ& O¡go H$åß`yQ>a H$m _m°ZrQ>a àmoJ«m_, POST
computer, POST (Power On Self Test), Boot- (nmoñQ>) (Power on self Test), ~yQ>ñQ´>on bmoS>a, BIOS
strap loader program, BIOS (Basic Input out-
put systems) etc. are few programs which a (~m`mog) Am{X & Bg_| Hw$N> J{UVr` {Z`§VmH$ ^r aI
ROM contains. It may contain Tables of some gH$Vo h¢ O¡go sin, cos ’§$³eZ, bm°J Am{X H$m _mZ My±{H$
mathematical constants like sin, cos function, nm°da Mbr OmZo na ^r BgH$s OmZH$mar Zï> Zht hmoVr,
logarithm etc. ROM is a Permanent or non- Bg{bE Bgo ñWm`r (Admînerb) Non-volatile
volatile memory because, when electric power
goes off the contents of ROM are not lost. There (Permanent) _o_moar ^r H$hVo h¢Ÿ& {ZåZ àH$ma H$s amo_
are many types of ROM available: CnbãY h¢…
1. Masked-ROM.
2. PROM
3. EPROM
4. EEPROM (E PROM)
2
Masked-ROM _mñŠS>-ROM
Masked ROM is a factory programmed \o$ŠQ´>r _| ~ZmVo g_` hr {Mn _| àmoJ«m_ {bI {X`m
ROM. A program is written into this ROM while OmVm h¡Ÿ& bo{H$Z EH$ ~ma àmoJ«m_ {bIZo Ho$ níMmV² Cgo
fabrication. Once the program is written it can n[ad{V©V Zht {H$`m Om gH$Vm h¡ & Eogm Z Vmo Cn`moJH$Vm©
not be changed. It is not programmable by any Ûmam Am¡a Z hr {H$gr AÝ` CnH$aU Ûmam {H$`m Om gH$Vm
other device. If a new program is to be written, h¡Ÿ& `{X EH$ Z`m àmoJ«m_ {bIZm h¡, Vmo ZB© ROM H$s
a new masked-ROM is needed. This is similar
to your text book. Because it comes “Printed” IC ~ZmZm n‹S>Vr h¡ Ÿ& `o AmnH$s nwñVH$ Ho$ g_mZ hr hmoVr
from the printing press. You cannot write on h¢ Š`m|{H$ `h {àpÝQ>¨J go N>nH$a AmVr h¡Ÿ& Bg na Amn
the pages of a book. If something new you Hw$N> {bI Zht gH$Vo {g\©$ n‹T> hr gH$Vo h¢Ÿ& `{X H$moB©
need, a new book is to be printed. ZB© OmZH$mar Mm{hE Vmo {\$a àog _| ZB© {H$Vm~ N>ndmZm
n‹S>oJr&