Machine will not boot - read this

[herbert]

I came across this at http://ic.doma.kiev.ua/inside/award/elist.htm

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How to protect FlashROM from recording?
It can be made but it is necessary to mean that BIOS can not to update ESCD and DMI blocks during a system reconfiguration.
FlashROM has an inverse input of Write Enable signal WE# Contact 31, it is possible to prohibit writing by disconnecting contact 31 and giving on it logical 1. For this purpose it is necessary to include the resistor approximately 1K between a + 5V and detached Contact 31.
It is not necessary to prohibit writing by detaching VPP Contact because
5-volt FlashROM do not use this contact and in this case VPP inside a chip is contacted to power supply VCC Contact 32.
Warning !
The guideline has force for chips Flash 1Mbit/2Mbit, issued in 32-contact DIPP or PLCC. The given guideline does not concern for Low Pin Count chips used in Intel 810/820, SiS730 and some other
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The point to note here is that the ESCD and DMI is written to the flash memory: Bytes are written to the BIOS "ROM". The PCGUIDE seems rather fuzzy about this. The PCGUIDE also states that the "CMOS" is NVRAM. This is not generally true. It's RAM. That's why there's a battery on the board.

These flash writes, that occur when the system is altered and rebooted, are dangerous. There is a potential disaster awaiting anyone who reboots a machine that is oveclocked or unstable.

It is a cheap fix on the part of motherboard designers to use spare capacity in the BIOS "ROM" to store this data. What's needed is another flash memory, separate from the BIOS. The BIOS should be write-protected by a jumper in the manner described above. Also, BIOS flash memories should ALWAYS be in sockets! Otherwise, when a bad flash occurs, a new motherboard is required rather than a $20 BIOS chip.

A message to all who can't boot:
Plug an ISA video card into the machine. You may well find the dreaded
"BIOS ROM Checksum error"
on your screen.

[PostCode]

Actually, the CMOS is quite Non Volitile. The CMOS and BIOS are two different things. The CMOS is the RAM that contains the setup instructions themselves. The BIOS is the RAM that contains the setup information that is defined, thus the battery. When you change something in the BIOS, these settings are not altered in the CMOS RAM, but in the BIOS RAM. When you flash the CMOS, your overrighting the setup routines that are part of the POST and other misc data.

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Eric's BIOS Post Codes (http://www.webenet.net/~ntuser)

[herbert]

The battery is there to maintain both the CMOS RAM and the realtime clock.

If the CMOS is non-volatile how come you can clear it by shorting a jumper?

[Paleo Pete]

Non-volatile does not mean totally unable to be changed, in the case of CMOS. If it were, you would be restricted to one hard drive, one floppy, etc since they could not be changed if replaced, or a second floppy added, such as my 5 1/4" drive for transferring data to the older XT/AT machines.

Since the CMOS stores info related to system configuration, which must necessarily be changed sometimes, it can be written, but only while accessing BIOS. All other times, it can only be read, therefore the data stored remains, and is kept active by the battery. If the battery goes, or CMOS is cleared, CMOS retains a default configuration that can then be reset.

Therefore clearing CMOS does not totally "clear" the data, simply resets it to the default configuration, which is a good thing when you totally toast your settings... The default configuration cannot be erased.

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Soon as I come up with all the answers...they change the questions!!

Computer Information Links (http://www.geocities.com/paleopete/)