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Shadow RAM

Reading time: 3 – 4 minutes

Tots hem entrat algún cop a una BIOS i hem vist una opció q
posa: Shadow RAM. Un altre problema és quan el tipic ‘newbie’ de turno
ens diu: q és akesta opció?

Nosaltres q representa q som uns gurús ens quedem blancs i pensem ni
zorra però si no ho poso va més lent tot….

Bé doncs, he trobat un article d’un d’aquests fieres de la
“infosmàtica” q ho explica l’article esta a geocities exactament

Com q geocities té una política molt rara a l’hora d borrar
pàgines tb ús l’adjunto a l’article pq no és massa llarg.
Aquí el teniu:

The Magic Of Shadow Ram

To start from,shadowing is a word many of us have come across while tweaking
with BIOS settings.In this article I will explain what actually is shadowing
and what effect it has on our system.

Importance of ROM

We all know that ROM’s are of great help to a computer.They support the
non-volatile state of the system.For example the BIOS ROM is the place where
the POST code,the BIOS settings and the infamous ROUTINES(interrupt)
reside.BIOS performs the POST during boot up.Now from here all the operating
system’s whose code I have read uses one or another BIOS routine.For example
the LINUX uses the INT 13h to load the boot code.So it is pretty evident that
codes residing in BIOS is of atmost importance.But the saddest part is that
ROM’s have lower speeds when compared to RAM’s.Here is where the need for
shadowing arises.

What is it really ?

Shadowing,as the word meaning denotes presence of a thing having some duplicate
form.The so called shadow will not have all the properties of the original.This
is also case of SHADOW RAM.First without shadowing ROM is accessed via memory
mapping.Memory mapping is that from the memory space of processor some area is
reserved for ROM.For example suppose (very wildly) we map our Systems memory
from 0- 5Kb for ROM access.So when we give the processor command to access the
area at 1Kb the system would automatily access the ROM code.So is the case
anywhere between 0 and 5Kb.Also the RAM over this area would be wasted.In
shadowing the code in the ROM would be copied to the RAM.If we consider the
above case,the code of ROM area would be copied to RAM at 0 – 5Kb.So when
access to 1Kb is made actual access is made to the RAM not to the ROM.But the
code executed would be same as it is the copy of what is in ROM.

Advantages of Shadowing

The increase in speed is obvious.The code when executed from ROM takes longer
time as the speed of ROM access is greater.When the code has been shadowed to
RAM the speed of execution naturally increases as access of RAM code takes
lesser time.Also RAM,in absence of shadowing may have been wasted is now
utilized to increase efficiency.

Pos ala això és tot a espero q ús agradi.

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