CMOSSave

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Introduction

CMOSSAVE is not a program for the naive user. You must be familiar with composing ASCII text command files and booting to DOS to be able to use it.

1. The most important fact is you must use CMOSSAVE BEFORE you have trouble. If you have not done so, CMOSREST won’t do you a lick if good once your CMOS is corrupted.
2. The second most important fact is you must boot from DOS and have access to the saved CMOS file on the boot diskette/CD in order to restore your CMOS.
3. The third most important fact is you must redo you CMOSSAVE any time you change your CMOS, e.g. upgrade your disk. You also need to redo your BOOTSAVE at the same time.

Author

Please report bugs and problems to roedyg@mindprod.com

Harvey Fishman wrote a pair of programs similar to CMOSSAVE and CMOSREST, but to the best of my knowledge, never released them.

Freeware Status

Tel: (250) 361-9093
mailto:roedyg@mindprod.com
http://mindprod.com

Big companies such as Sony, NCR and Chemineer use cmossave to protect all their machines and to clone CMOS settings across machines.

Warranty and Support

Keep in mind, CMOSSAVE won’t do you any good unless you have used it before you have trouble. I have no magic to bail you out after the fact. Pleading with me won’t help.

Happily, so long as you have done a CMOSSAVE, and have not overwritten it, almost any problem can be recitified even if CMOSREST or CMOSCHK should fail.

Getting the Latest Version

Purpose

1. Naive users sometimes fiddle with CMOS settings. We need a fast way to put the scores of subtle CMOS configuration settings back the way they were.
2. Power surges can corrupt CMOS. We need a way for a naive user to quickly restore all the CMOS settings.
3. If the battery fails, the contents will be lost. We need a way to restore a known working CMOS configuration.
4. You may want to alter some obscure CMOS setting and you don’t have a program to set it.
5. CMOSRest can also be used to toggle between two CMOS configurations, for example with and without a removable hard drive installed. If you had removable hard disks, you could rapidly switch between the various disks.
6. CMOSChk can detect subtle corruption to CMOS, as might be caused by a rogue program or a virus, something that might slow your machine or make it unreliable.
7. CMOSSave can create a backup of your CMOS on floppy. This way you may safely experiment with CMOS settings. You can always get back to where you started by using CMOSRest to restore the original settings. Any time you fiddle with the computer innards, you might accidentally disconnect the battery, losing CMOS. CMOSSAVE lets you put it back the way it was.
8. Testing a machine for year Y2K 2000 compliance, to make sure the BIOS will kick the date over properly in the year 2000. Not so important anymore.
9. If you build machines for a living, you can rapidly clone the CMOS settings of one template machine in a dozen others. You create a DOS bootable removable device (floppy, USB drive etc), with a copy of CMOSSAVE.com and CMOSREST.com on it. You set up one machine, do a CMOSSAVE to the DOS bootable device, then insert that device into each machine to clone, boot and do a CMOSREST.

What Is CMOS?

The data in CMOS RAM can only be examined or changed with a special program such as CMOSSAVE. It is not a file. If you are curious about how CMOSSAVE does the access, have a look at the notes in the source code in CMOS.ASM.

When the battery dies, or does when a recharegeable battery not get sufficient on time to recharge, the CMOS fails, and it forgets all it knows about your configuration.

CMOSSAVE is designed to restore this lost information by storing copies of it on floppy and/or hard disk.

Syntax

/Q suppresses unnecessary banner messages.

Hints

1. manually,
2. automatically
3. with a rescue diskette.

1. Manually. Prepare a bootable floppy with the command:
   Format A: /S /V /U /F:1.44MB
   Unfortunatly Windows NT W2K, and XP can no longer create a bootable DOS floppy, though Vista and Windows 7 can. Borrow a DOS bootable disk from someone with FORMAT on it, and duplicate it or boot from it to create another bootable dos floppy, or get a friend to create you a bootable DOS floppy with W98 or WindowsME.) Install CMOSSAVE.com and CMOSREST.com on your hard disk into C:\com\mindprod\cmossave. You can create such a directory with:
   MD C:\com\mindprod\cmossave
   This directory need not be on the path, but if it is not, you will have to type
   C:\com\mindprod\cmossave\CMOSSAVE
   instead of just
   CMOSSAVE
   Backup your CMOS to the bootable floppy with:
   CMOSSAVE.com A:\CMOS.SAV
   COPY C:\com\mindprod\cmossave\CMOS*.com A:
   CMOSSave is a DOS utility and thus can only use short 8.3 file names. If ever your cmos becomes corrupted, correct it by booting DOS from floppy and typing:
   CMOSREST.com A:\CMOS.SAV
   CMOSRest is a DOS utility and thus can only use short 8.3 file names. Then reboot. In this case you don’t bother with CMOSCHK.com at all.
2. With a rescue diskette. Prepare a bootable DOS floppy with an autoexec.bat that invokes the following commands to correct most CMOS and hard disk problems with DOS:
   CMOSREST A:\CMOS.SAV
   BOOTREST A:\BOOT.SAV
   CHKDSK C:/F
   SYS C:
   COPY A:\COMMAND.COM C:\
   COPY A:\COMMAND.COM C:\DOS
   
   (BootRest.com freeware is separately available. You need to make a separate rescue disk for each machine unless the machines are absolutely identical including hard disk size.

Belt and Suspenders

At that point you must reboot before the restored cmos settings take effect. Sometimes CMOS will be so badly damaged the hard disk parameters will be corrupt and your hard disk will stop working. In that case you will have to revert to using the floppy copy.

Whenever you change your CMOS setting deliberately, you need to redo the CMOSSAV.COM. However use a new filename, so that you can easily revert to the old version if your new settings do not pan out.

Running Under DOS

1. CMOSSave is a very old program, that was created in the DOS days, before Windows was a twinkle in Bill Gates’ eye.
2. CMOSSave will run under Windows, it is just that the Windows OS now prevents it from accessing or changing CMOS, making it useless. Windows does this to protect CMOS from malicious corruption by malware. Windows has no way of knowing that CMOSSave is benign.
3. Windows itself will usually not run at all if CMOS is corrupted. If CMOSRest ran under Windows it would not be able to run to restore CMOS.

• Boot from a DOS system floppy

  DOS system diskettes use FAT-16 format, 512-byte clusters, with a DOS system image. You can get a DOS System floppy by looking in your collection of old DOS floppies and duplicating it. If you don’t have one, you can ask a nerdy friend who does. If you don’t have a bit-for-bit copy utility, you can boot from the DOS floppy, and use the following command to format a new system diskette:
  rem X: is the floppy drive, insert a blank diskette when prompted
  format X: /S
  You can also create one under Windows with Computer ⇒ select drive ⇒ right click format ⇒ Create MS DOS Startup Disk. The command line format command is not suitable since it has no option to create the DOS system disk.

• Boot from a USB Flash drive that is formatted to look like a DOS system floppy

  What if your computer does not have a floppy drive? You could temporarily install one. Alternatively, it will have a free USB port. Buy a small USB flash drive. Even the tiniest 1 MB model will do. The problem is getting it formatted to look like a DOS floppy. The Windows format refuses to do it. I could not find a utility to do it with my SanDisk Cruzer. If you find a source for USB Flash drives with a bootable DOS pre-installed, please let me know. If you find a public domain version of DOS designed to be installed on a flash drive, please let me know. Not many people have both an old copy of DOS and a floppy drive any more.

• Boot from a DOS system partition on hard disk

  Creating a DOS partition on hard disk is not for the beginniner. You need a Partition/Boot mananger to pull it off.

• Boot from a DOS system on CD ROM

  Booting from CD-ROM may require a special version of DOS that will treat a CD like a read-only floppy. Again, this is an advanced technique.

How It Works

Modern computers have larger CMOS memories than 128 bytes, but you access them via proprietary ways, which CMOSSAVE does not know. So CMOSSAVE just saves the first 128 bytes, which are accesses in a uniform way on all PCs.

CMOSREST does not touch bytes 0 to 09 and 32h because these are volatile — they contain the date and time. Similarly CMOSCHK, does not panic if any of these volatile bytes differ. However, CMOSSAVE saves all 128 bytes, so that you can browse the generated file with a hex editor to learn more about how CMOS works.

You need some sort of hex viewer to see the contents of the CMOS.SAV file. The hex list of bytes is not that meaningful if you are not a computer programmer.

Daring users could even patch the CMOS.SAV file with a hex editor and restore to get special effects, e.g. to switch between two different CMOS configurations e.g. one with and one without some hard disk. Don’t attempt to edit the file with a non-hex viewer such as NotePad, WordPad, Write or Word For Windows. If you do, you will scramble the file beyond recognition.

Because CMOSSave also saves the extended CMOS bytes, CMOSRest will restore the esoteric options like shadow RAM, wait states, processor clock speed, HMA enable etc. It works on ISA, EISA and PCI machines.

These is no need for any of the three utilities to calculate checksums, since the checksum is saved and restored just like any other CMOS byte.

You might wonder why CMOSSave saves only 128 bytes of CMOS even though some modern computers have many times that amount. The problem is the way you get at the rest of it is proprietary. The vendors won’t disclose how you get at it. It is possible to disassemble the ROM BIOS to figure it out in an individual case, but that won’t work on other machines. So it is usually not worth the bother unless you wanted a special version of CMOSSAVE for thousands of identical machines.

How to Use CMOS

See CMOS.OFS for a detailed list of what each byte in the CMOS is used for. This is usually of interests to technophiles only.

DOS Bootable Device

• A tiny DOS partition on hard disk.
• A Bootable DOS floppy.
• A bootable DOS USB flash drive.

1. Copy an old DOS bootable floppy, deleting any files you don’t need.
2. Format an empty floppy with Windows, ticking off the DOS-bootable option. It will have a FAT16 files system with 512-byte sectors.

1. Download the free USB formatting software from ExtremeOverclocking.
2. Download the DOS boot files for Windows 98 from the same place.
3. Use the software to format a USB drive as a bootable DOS drive.
4. Copy CMOSave.com, CMOSRest.com and CMOSChk.com to the USB drive.
5. Adjust your BIOS to boot from the USB drive.
6. Boot from the USB.
7. Do your thing with CMOSSave.
8. Adjust your BIOS to boot from hard disk again.

Troubleshooting

What is considered volatile and what is not, might vary for different motherboards. If you have trouble restoring, Do not despair. All is recorded. A variant of the CMOSREST program could get you back. All you need do in make a slight modification to the assembler source VOLATILE routine that decides which bytes to consider volatile. Even a very junior MASM programmer could make that modification for you using the assembler source.

If you do a CMOSSAVE from the DOS prompt and from true DOS there may be some subtle differences, and CMOSCHK may complain about them. This is nothing to worry about since when you restore, those bits in the CMOS will be automatically corrected the next time you boot to either DOS or Windows. It is quite safe to save from the DOS prompt with CMOSSAVE, check with CMOSCHK from autoexec.bat or other bat file, and do your restore with CMOSREST from true DOS.

Sometimes your CMOS will be so wrecked you cannot even get your machine limping enough to run CMOSREST from floppy. In that case you must clear CMOS. Do this on AMI BIOSes by holding down the INS key, powering off, powering on, then releasing the INS key. In the worst case, remove the battery and let the capacitance on the board drain overnight to clear it. On some CMOSes you can clear CMOS by selecting universal default settings from the normal CMOS setting menu.

You can then get a bare bones CMOS configured — that just has the floppies right. Nothing else much matters. From there you can run CMOSREST.COM.

The SSTOR disk formatting utility from Storage Dimensions makes it look as though it had modified CMOS. If you boot without the SSTOR driver, CMOS will appear to have changed because SSTOR is not doing its standard trickery.

The NCR CMOSDR6X program interferes with CMOSSAVE and CMOSREST. Make sure you do your CMOSSAVE CMOSREST work before loading this program.

The TURBO setting is part of CMOS. If you accidentally turn turbo mode off, CMOS will appear to be changed, and CMOSCHK will complain. To clear the problem, set turbo back on and allow the CMOSCHK to restore CMOS. This way CMOSCHK will remind you if you have accidentally turned off turbo mode. This feature can be turned off by making the byte where your turbo info is stored volatile. If you want this feature, just send the CMOSCHK listing that complains about CMOS being changed.

CMOSREST does not take effect until you REBOOT!!

Getting Help From Roedy

• A description of the problem.
• A description of your hardware motherboard and OS.
• attach a screenshot (image or text) of the offending command and any error message.
• attach a copy of your cmos.sav file and a copy of a second cmosb.sav file taken a few minutes later.

Verification Fire Drill

False Alarm CMOSChk Corruption Messages

1. Send me a screen print of what CMOSCHK is saying. I will send you a custom version with those false mismatches considered as volatile bytes.
2. Modify the VolatileList line in CMOS.ASM yourself to include the extra offsets your BIOS is treating as volatile. Then reassemble. CmosChk.com will give you a list of offsets where it thinks there are mismatches. It is up to you to determine which ones you think are false alarms.
3. Simply avoid using CMOSChk. Just use CMOSSAVE and CMOSREST. Most of the time damaged CMOS is fairly obvious.

What If You Have Already Crashed?

You had best get an expert to help you set the CMOS back to defaults and guess the fine tuning for the parameters. The dealer who sold you the machine is the best person to help. He may be able to contact the disk manufacturer to find out how many heads and cylinders it has. He may be able to find hints in the motherboard manual.

If your machine has an exact twin, you may still be in luck. You can make a backup of the CMOS on that machine, then restore it into the ruined one. Don’t try this unless the machines are absolutely identical. There is a good chance you will destroy your hard disk data if you transplant a CMOS from a different sized disk.

You can manually set CMOS back if you hit the magic keys during hard boot, often DEL, F2, or Ctrl-Alt-Esc. Sometimes you need a diskette to set up CMOS. Check the manual that came with your motherboard, or check with the company that sold it to you.

Usually there is a way to set CMOS settings to default. In a pinch you can do it by removing the battery for a day or two.

WINDOWS 95/98/ME

Windows 95 still has a C:\autoexec.bat just as under DOS. Alternatively go into a DOS box and use the CMOSSSAVE utilities just as you would under DOS to add the call to CHKCMOS.BAT or to directly invoke CHKCMOS.COM. still use CMOSSAVE and CMOSREST just as under previous versions of DOS and Windows. Putting cmoschk.com in your autoexec just helps you detect cmos corruption the instant it occurs.

Windows 95 users often have no understanding of the DOS CD, MD and path commands, how to edit autoexec.bat or even how to run a DOS program. If you are one of this new breed, your best bet is to get help from someone who is familiar with DOS, since if CMOS is corrupt you will need to revert to DOS to get Windows going again.

You can run the utilities either in autoexec.bat, in DOS or 4DOS box, in a BAT file, or by creating a shortcut, complete with parameters on the command line.

However, here is a crude, but fool-proof recipe to use cmossave manually under Windows 95.

Copy the files cmossave.com, cmoschk.com and cmosrest.com to a freshly formatted floppy in your A: drive.

In Win 95, select Start, Programs, MS DOS Prompt to get you to the Win 95 DOS box. Type:

Windows NT/2000/XP/Vista

You can acquire a bootable floppy by digging in your old DOS diskettes, asking an old timer for one, or you can right click Format and select ‘bootable DOS disk’. It may be possible to use memory sticks, thumbdrives, CDs and DVDs too with approriate DOS-formatting software.

Modern Large CMOS

Y2K Year 2000 Compliance

If you are testing a number of machines, make sure you erase the CMOS.SAV file on floppy between tests. You don’t want to accidentally restore the CMOS.SAV file from one machine into another (unless they were absolutely identical, including hard disk size.)

XT Computers

You can configure XT floppies using DOS’s DRIVPARM.

Back in the good old days of the XT you had to use proprietary methods to format hard disks and tell DOS how big they are. Typically you fired them up with debug g=c800:5 and talked with a proprietary ram-based low level formatting program. Then you later used DOS format. HDSNIFF goes into this in much more detail. Briefly:

Repeated Failures

• a poor battery. Replace it with a lithium battery. (You will need the motherboard manual, because sometimes you need to change a jumper when you do this. If you have a nicad rechargeable battery, leave the machine on all the time to give it time to recharge.
• a roque program. A program going nuts can accidentally write garbage into CMOS. I have found this is less likely to happen with Windows 95.

CMOS Offsets. How each byte of CMOS is used

! = must be restored
* = checksummed
v = volatile

CMOS Offset Notes

To access the configuration RAM write the byte address (00-3Fh) you need to access to I/O port 70h, then access the data via I/O port 71h.

CMOS RAM chip is a Motorola 146818

The equipment byte is used to determine the configuration for the POST power-on diagnostics.

Bytes 00-0Dh are defined by the chip for timing functions, bytes 0Eh-3Fh are defined by IBM.

compaq 386 uses the same cmos chip as ibm at. extra functions:
byte 45 (2Dh) store additional info not maintained by AT
bit 0 indicates is Compaq dual-mode monitor insttalled
bit 1 indicates whether keyclick is enabled
bit 2 not used
bit 3 if non-Compaq graphics adapter installed

Some CMOSes, (SXs) appear to store duplicates of registers 0:3F in 40:7F, others (DXs) store some other advanced configuration information in these registers. Thus there are 64 byte and 128 byte CMOSes. We tell them apart by looking for a match in bytes in the checksum range.

Offsets 10..2F are included in the checksum. We do not ever need to compute a checksum in CMOSREST since we just save and restore. Exactly what is included in the checksum varies with the BIOS. Sometimes only 10..20 is included.

For further information see the IBM AT Technical reference page 1-56. PC Magazine did an article on CMOS on page 344 of the 1994-09-13 edition.

For a detailed list, especially for vendor specific bytes is in The Undocumented PC, A Programmer’s Guide To I/O, CPUs, and Fixed Memory Areas by Frank van Gilluwe, Addison-Wesley. For exhaustive detail, see CMOS.LST available as part of Ralf Brown’s interrupt list:

You can modify the VOLATILIST in CMOS.ASM if you find other volatile bytes in your cmos, in other words, bytes in CMOS that seem to change even when cmos is not corrupted.

Note to Computer Manufacturers

You can rapidly clone the CMOS settings of one template machine in a dozen others. You create a DOS bootable removable device (floppy, USB drive etc), with a copy of CMOSSAVE.com and CMOSREST.com on it. You set up one machine, do a CMOSSAVE to the DOS bootable device, then insert that device into each machine to clone, boot and do a CMOSREST.

Extended CMOS

Books

	recommend book⇒The Undocumented PC, A Programmer’s Guide To I/O, CPUs, and Fixed Memory Areas
		paperback
	ISBN13:	978-0-201-62277-5
	publisher:	Addison-Wesley
	published:	1993
	by:	Frank Gilluwe
A fasciting book about CPU detection, undocumented CPU instructions, how adapter cards work, how the BIOS works, how DMA works and of course how CMOS works and how the various parts of CMOS are used.
abe books.co.uk abe books.ca amazon.co.uk amazon.ca abe books.de chapters.indigo.ca amazon.de abe books.com abe books.fr amazon.com amazon.fr barnes and noble.com abe books.it powells.com iberlibro.com sony e-books abe books anz

	You can get the freshest copy of this page from:	or possibly from your local J: drive (Java virtual drive/mindprod.com website mirror)
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	Please email your feedback for publication, errors, omissions, typos, formatting errors, ambiguities, unclear wording, broken/redirected link reports, suggestions to improve this page or comments to Roedy Green :
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