Re: Somrthing altered my BIOS settings

JohnO wrote:
Fair enough, there are always exceptions.

I have worked with a dozen various Intel boards, some MSI, a couple ASUS, and a mess of Soyo boards going back to 1996, and they all worked as I described. Maybe I was just lucky. :-)

I am truly curious how many of the P4-era boards use flash RAM vs CMOS RAM. I'm working on a book that will be seen by ~40k students each year, and I'd like to get this right.

-John O

I suggest reading a data*** for a Southbridge, before you write that book.

http://www.intel.com/design/chipsets/datashts/252516.htm

"RTC

The ICH5 contains a Motorola MC146818A-compatible real-time clock with 256 bytes
of battery backed RAM. The real-time clock performs two key functions: keeping
track of the time of day and storing system data, even when the system is powered
down. The RTC operates on a 32.768 KHz crystal and a separate 3 V lithium battery.

The RTC also supports two lockable memory ranges. By setting bits in the
configuration space, two 8-byte ranges can be locked to read and write accesses.
This prevents unauthorized reading of passwords or other system security information.

The RTC also supports a date alarm that allows for scheduling a wake up event up
to 30 days in advance, rather than just 24 hours in advance."

On page 4, you can see the flash BIOS is connected to the LPC bus. (Low pin count,
four bit wide data bus.) The flash BIOS is a separate entity, from the RTC. The
flash BIOS is a 512KB EEPROM on my motherboard, while the RTC is a separate
CMOS static RAM inside the Southbridge.

The Flash BIOS contains main BIOS code, boot block code, DMI/ESCD, microcode cache.
The last two are volatile, in the sense that, when the computer POSTs, the BIOS
may choose to flash update those sections itself. For example. say yesterday you
had one stick of RAM in the computer. You power off, and install a second stick
of RAM. When you start the computer, the POST may mention updating something. It
will be correcting the inventory information stored in the DMI/ESCD.

The microcode cache, was a BIOS call and feature, used on my 440BX board. When the
correct microcode is detected, for a newly installed processor, it is flash updated
into a couple 2K segments in the flash chip. It is possible, without altering the main
BIOS code, for a user to actually install their own microcode. This was useful in the
Tualatin era, for providing microcode support, when the motherboard manufacturer was
no longer willing to update the BIOS properly (as there is also a module which is
part of the main BIOS code, which contains typically 8 different microcodes).

Microcode is now larger than 2K, and Intel has made the size variable. So I'm not sure
the same feature exists. (And support for it differed between Award and AMI.)

And these are all things I discovered, while just fixing my home computers :-)

If you want a simple experiment to start with, try flashing your BIOS. You can
even use your current version if you want. First, download the BIOS to use.
Flash upgrade the BIOS. Now, let the computer POST at least once. Using the
BIOS flash tool, make an archive copy of the BIOS. Do a binary compare of the
originally downloaded flash file, and the archive copy you just made (after
computer POSTed at least once). The files differ. The section of the BIOS
that is different, should be showing you the DMI and ESCD (volatile) sections.
The BIOS updated them, during the first POST cycle.

There is an infinite amount of trivia associated with the low level details
of PC hardware - if you're writing a book, you'll need plenty of "old farts"
to proof read it for you.

Paul


"RalfG" <itsnotme@xxxxxxxxxxxxx> wrote in message news:e5YBHuMaIHA.4180@xxxxxxxxxxxxxxxxxxxxxxx
Some PCs may use flash memory, not all of them. Removing the battery sometimes does not work immediately because the PSU connected to the motherboard can hold enough of a charge to keep the stored settings intact for several hours after the battery is removed. Depends on the circuit configuration of course. Removing the battery for just a few seconds cleared the CMOS for me on one PC a few weeks ago (an Athlon board, c.2002-3).

"JohnO" <johno@!NOOSPAM!heathkit.com> wrote in message news:uerk5XMaIHA.5348@xxxxxxxxxxxxxxxxxxxxxxx
Bios settings are held in the cmos, a form of RAM. The cmos battery maintains life of the RAM while the PC is physically off. Its on the motherboard.
No, the battery keeps the real-time clock running, and that's it. The data held in BIOS is non-volatile flash RAM, and remains intact forever whether the battery is present or not. That's why the BIOS reset jumper exists, otherwise we could just remove the battery and clear the BIOS settings, but that doesn't work.

I'm surprised at some of the responses in this thread. :-)




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