a Tech Question

So, bottom line is....
The Rom(bios) has within itself some Ram (called cmos) of which is able to
be fiddled with by the user..... yeah?

"Mart" wrote in message
...
Interesting (personal) insight Ian - thanks for your follow-up which makes
sound technical (but not seemingly, commercial g) sense.

Mart


"Ian Shef" wrote in message
0...
"shep" wrote in news:#58NBrkMHHA.4384
@TK2MSFTNGP03.phx.gbl:

Thanks to all repliers.

I still have a couple of things that are bugging me, will post back
when I can word my concern correctly.


"shep" wrote in message
...
Hi,

I was reading up on the difference between BIOS & CMOS, and think I
now how a grip on it, but I am wondering why the cmos/config program
uses ram instead of rom?
Wouldnt this do away with the necessity of the cmos battery?

thanks for any enlightenment.





This scheme was developed at a time when nonvoltaile memory was either:
EEPROM - handy but expensive at the time
UV eraseable EPROM - expensive, and requires UV light to erase.
PROM of various types - handy for the BIOS, but not reprogrammable
RAM with battery backup - relatively inexpensive
others - expensive or required too much room or carried too much
overhead

A battery was required anyway to keep the calendar/clock running, so RAM
with battery backup made good economic sense.

Nowadays, the RAM, calendar/clock and other items are integrated
together
in one chip. Putting flash memory into the chip would drive up the
cost.
Putting external serial flash memory external to the chip would be handy
but would also drive up the cost a little.

[Personally, I would prefer to have these parameters in flash so that
they
are not lost in the case of a battery failure, but cost seems to have
pushed the vendors in the other direction.]


--
Ian Shef 805/F6 * These are my personal opinions
Raytheon Company * and not those of my employer.
PO Box 11337 *
Tucson, AZ 85734-1337 *

"shep" wrote in :

So, bottom line is....
The Rom(bios) has within itself some Ram (called cmos) of which is able to
be fiddled with by the user..... yeah?

Conceptually, yes. In reality, no.

The BIOS is software that is stored in nonvolatile memory (nowadays, Flash
memory). It is executed by the CPU, which has access to various pieces of
hardware. One of these pieces of hardware acts as an interface to some CMOS
RAM (with battery backup). The hardware piece that acts as an interface to
the CMOS RAM often also contains the real time calendar/clock that must keep
running (by battery backup) when the PC is off.

A user can use the Setup feature of the BIOS to "fiddle with" the CMOS RAM
(because the Setup feature is really just a program running on the CPU).
If permitted by the OS, the user can even access the hardware to more
directly "fiddle with" the CMOS RAM, but this is dangerous.

Why did I say dangerous? Losing settings is one obvious danger of fiddling
with the settings. Other dangers include (on some machines) setting CPU
voltages or clock speeds too high and causing permanent damage.


--
Ian Shef 805/F6 * These are my personal opinions
Raytheon Company * and not those of my employer.
PO Box 11337 *
Tucson, AZ 85734-1337 *