What is the difference between nvram and cmos?

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pml

Are there any differences between nvram and cmos (if so what may they
be)?

How should the nvram be cleared (by jumper/bios or other way?)?

What relation does the bios have to nvram and cmos?


What happens inside the computer when the nvram is cleared? I know the
settings are sent back to default, but I mean from a more technical
perspektive.
 
pml said:
Are there any differences between nvram and cmos (if so what may they
be)?

How should the nvram be cleared (by jumper/bios or other way?)?

What relation does the bios have to nvram and cmos?


What happens inside the computer when the nvram is cleared? I know the
settings are sent back to default, but I mean from a more technical
perspektive.
Click to expand...


http://www.pcguide.com/ref/mbsys/bios/compCMOS-c.html

Lots to read at pcguide.com. It doesn't have all current hardware
described (SATA is missing) but eventually the author will get to it.

(Trick: when searching their site, add "-forum" to the search string to
eliminate getting posts from their forums if you just want to read the
author's articles.)
 
pml said:
Are there any differences between nvram and cmos (if so what may they
be)?

How should the nvram be cleared (by jumper/bios or other way?)?

What relation does the bios have to nvram and cmos?


What happens inside the computer when the nvram is cleared? I know the
settings are sent back to default, but I mean from a more technical
perspektive.
Click to expand...



Isn't CMOS just a type of NVRAM?
 
NVRAM is non-volatile RAM. Holds its values
when powered down. CMOS is just a type of
memory, albeit low power, but it does require
battery backup.
 
Alceryes said:
Isn't CMOS just a type of NVRAM?
Click to expand...


Non-volatile RAM simply means it doesn't lose its values (or state) when
the system power is removed. That does NOT preclude the use of
batteries. NVRAM is *any* random-access memory that retains its state
when main power is removed regardless of the technology used to
implement that memory. ROM, PROM, UV-EPROM, EEPROM, and even CMOS (with
battery) qualify as NVRAM. While ROM, PROM, UV-EPROM, and EEPROM do
qualify, NVRAM usually means memory that requires a battery to provide
power to retain state when the main power is removed. In some cases
with a small memory size for CMOS, even a capacitor can be used
depending on how long is needed the retention period (week, month, or
year). NVRAM even includes the ferromagnetic beads used in old
mainframes back in the '50s and '60s. Magnetic bubble memory was also
NVRAM. While hard disks qualify as ferromagnetic non-volatile memory,
the "R" in NVRAM means random (for access) and that doesn't apply to
mass storage subsystems (hard drives, floppy drives, zip drives, tapes,
CD-ROM/RW).

When using the NVRAM term, you are encompassing a lot of different
memory technologies used to retain state when power is removed. It's
like saying human (all homosapiens) of which Inuit (an Eskimo tribe) is
part. NVRAM does not much narrow the focus of what technology is used
to retain state after loss of main power. NVRAM defines an effect, not
how implemented. CMOS w/battery is just one of many ways to implement
non-volatile random-access memory. So, yes, CMOS is just a type of
NVRAM as long as a battery (or capacitor) is also employed to retain
state when the main power is removed.
 
On 30 May 2005 05:30:50 -0400,
Are there any differences between nvram and cmos (if so what may they
be)?

How should the nvram be cleared (by jumper/bios or other way?)?

What relation does the bios have to nvram and cmos?


What happens inside the computer when the nvram is cleared? I know the
settings are sent back to default, but I mean from a more technical
perspektive.
Click to expand...

CMOS is used to decribe a technology of manufacturing, the
construction of the chips. Then there is another context,
how it's used in computer (use and configuration rather than
building circuits). The relevance here is that the typical
BIOS EEPROM (chip) is a CMOS device, but when one refers to
CMOS as-in "clear CMOS", they mean to clear the volatile
memory device allocated separate from main system memory.

So you have nvram not actually being non-volatile or not.
being "ram" rather than ROM.

The BIOS is firmware specific to the motherboard's built-on
hardware. It's stored in a flash-CMOS type EERPOM chip on
modern systems. When the system boots it loads this into
memory and then it accesses the CMOS RAM which holds
user-configurations from the bios setup menus, and further
*variable* parameters such as amount of memory installed,
CPU, HDDs, RTC (real time clock), operating frequencies in
some cases, etc.

By clearing CMOS you are removing power to it, so it's data
(temporary, volatile state) is lost. Then when the firmware
reads the CMOS contents, it finds nothing to change from the
default values it already had, and proceeds to use the
default values, update the CMOS in whatever ways it would
each time it runs, and perhaps prompt the user of this empty
CMOS so that initial configurations necessity (or potential)
can be noted by the user.

Supposing a cleared CMOS has all values of "FF", then a BIOS
might use a logic something like:

If FSB setting read from CMOS <> FF,
then use read value w/table-lookup,
else use table default

Then again I might be completely wrong about this last part,
I don't write bios.
 
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