Page 357 - FUNDAMENTALS OF COMPUTER

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NPP Memory 357

large number of references are made from cache H$_ hmoVm h¡ & `{X Ho$e go ao\$aoÝg H$s EH$ ~hþV ~‹S>r
then the overall program execution speed will g§»`m ~Zm`r OmVr h¡ Vmo gånyU© àmoJ«m_ H$s EŠOrŠ`yeZ
approach to the speed of cache memory. ñnrS> Ho$e _o_moar H$s ñnrS> VH$ nhþ±M Om`oJrŸ& `Ú{n Ho$e
Although the cache memory is put in a very _o_moar ~hþV H$_ _mÌm _| cJm`r OmVr h¡Ÿ& {H$ÝVw BgH$s
small size. But its speed will dominate over the J{V ao\$aoÝgog H$s ~‹S>r g§»`m Ho$ H$maU _w»` _o_moar H$s
speed of main memory because of a very large
number of references. J{V na AnZm à^wËd H$a coJrŸ&

Caching Systems Ho$qeJ {gñQ>_
A system containing cache memory, CPU Eogo {gñQ>_ {OZ_| CPU _oZ _o_moar VWm Ho$e _o_moar
and main memory is called caching system. H$m Cn`moJ {H$`m OmVm h¡, Ho$qeJ {gñQ>_ H$hcmVo h¢&
The size of main memory is large as compared _w»` _o_moar H$m AmH$ma Ho$e H$s VwbZm _| A{YH$ hmoVm h¡Ÿ&
to cache. There are two types of cache system
in use: Ho$qeJ {gñQ>_ Xmo àH$ma Ho$ hmoVo h¢:
(1) Using Level-1 (L-1) Cache (1) L-1 Ho$e dmbo (bodb-1 Ho$e dmbo)
(Internal Cache) (Am§V[aH$ Ho$e dmbo)
(2) Using Level-2 (L-2) Cache. (2) L-2 Ho$e dmbo (bodb-2 Ho$e dmbo)
(External Cache) (~mhar Ho$e dmbo)
L-1 Cache (Internal Cache) L-1 Ho$e (Am§V[aH$ Ho$e)
When the cache memory is built on the O~ Ho$e _o_moar H$mo CPU H$s {Mn na hr ~Zm {X`m
CPU chip, it is called L-1 cache. It is fastest in OmVm h¡ Vmo `h L-1 Ho$e H$hbmVr h¡Ÿ& BgH$s J{V g~go
the system. The following diagram shows it:
A{YH$ hmoVr h¡Ÿ& {ZåZ {MÌ _| Bgo ñnîQ> {H$`m J`m h¡:

L-1 Bus
Cache
Main
Memory

CPU Chip
(microprocessor)

CPU chip is called microprocessor or CPU H$s {Mn H$mo _mBH«$moàmogoga `m àmogoga H$hVo
sometimes processor. The L -Cache is made h¢ Ÿ& L Ho$e Cgr VH$ZrH$s go ~Zr hmoVr h¡, {Oggo
1
with the technology that is used for CPU chip. 1
Thus, the speed of L -Cache is same as the àmogoga ~Zm hmoVm h¡Ÿ& AV… BgH$s J{V dhr hmoVr h¡ Omo
1
speed of CPU. e.g. In Pentium a 256 KB of L - CPU H$s hmoVr h¡ Ÿ& O¡go 80486 _| 8KB H$s VWm n|{Q>`_
1
cache is available. In 80486 it is 8 KB. _| 256 KB H$s L Ho$e hmoVr h¡Ÿ&
1