Old 486 with DOS 6.X won't boot

[morningman]

I have an old 486 that won't boot to the C drive.
Can't even get it to recognize the C drive after start up from the A drive (big floppy). I can change to the B drive (small floppy). I'm not sure what to do as I have backup disks but seem to be of no use. Can I format the C drive even thou I can not pull a directory of the c drive?

[Platypus]

You'll get the symptoms you're experiencing if the BIOS has lost the Hard Drive parameters. (Unfortunately also if several other things have occurred, including hard drive failure.)

If instructions to press a key to enter the Setup appear on the screen when first turned on, use that to enter the BIOS Setup & see if there are Cylinder, Head & Sector settings for the hard drive. On older 486 systems, if these figures are not present, you often need to go to another section of the Setup Menu to Auto Detect the hard drive.

If there's no information about gaining access to the BIOS, let us know the type of computer and we can suggest some possible access methods.

[Dexahol]

Hi morningman, don't forget that the BIOS battery doesn't last forever. I can't tell you how many times this has been the problem of peoples 'puters that I've "fixed". Generally, its a good idea to replace it every year. They're not that expensive.

Then do what platypus said. Keep in mind though, many older 486's didn't have the "auto" feature. You may have to enter the parameters manually. If they're not printed on the top of the drive most hard drive manufacturers supply this info in the "legacy" section of their web sites.

Dexahol

[Robert M]

The BIOS does not require a battery but the CMOS chip usually does. When you enter the BIOS, changes can be made to the battery backed memory of the CMOS chip if you save when exiting.

The CMOS battery in my 486 is the original one, and has never been replaced over the past ten years. The motherboard manual that came with the computer says that it is rechargeable. The computer has never lost any hard drive parameters due to a weak battery.

Do you arrive at a prompt such as a:\> or similar?
What happens when you try the following and press the <ENTER> key?
c:

What type of computer is it?

[Dexahol]

Hi Robert, I'm not sure if we're talking semantics here, but my understanding is: the BIOS (built in operating system), is the "code" stored in the chip thats built using CMOS (complimentary-symmetry metalic oxide substrate) topology.

In the current computer vernacular, the BIOS and CMOS are essentialy, one and the same. The BIOS has non-volatile "default" values, and then the customer set values that are held in memory using the battery. The hard drive settings are one example of these settings. When the battery goes dead, the settings are "lost".

And of course, if the battery is rechargeable, (very rare), then you don't need to replace it.

Dexahol

EDIT: You know Robert, you got me thinking. So I checked out the Phoenix BIOS website, and they said this:

CMOS is a special kind of memory maintained by a small battery after you turn the computer off. The BIOS uses CMOS to store the settings you select in Setup and to maintain the internal real time clock (RTC). Every time you turn on your computer, the BIOS uses the CMOS settings to configure your computer. If the battery charge runs too low, the CMOS contents will be lost and POST will issue a "CMOS invalid" or "CMOS checksum invalid" message. If this happens, you may have to replace the battery. Contact your manufacturer for assistance. After the battery is replaced, the proper settings will need to be restored in Setup.

This supports what you said exactly. I always thought they we're one and the same physical chip, but now I don't think so. The BIOS chip itself is usually easy to spot, having the Phoenix or Award sticker on it, but I wonder which chip now is the memory, or CMOS, chip. Hmmm . . .

[Platypus]

The CMOS memory is usually contained in the RTC (Real Time Clock) chip, as this is also a CMOS device. The clock and CMOS memory are both maintained by the same battery, which on older boards was often also in the RTC.

morningman, if you get it operating, then after being off for a while it loses the settings again, that would indicate the backup battery is gone, as discussed above. Unfortunately a lot of old boards like this used block type RTC chips with the battery sealed in them. They're usually black and made by companies like DALLAS, HOUSTON TECH, ODIN, so if you need to change the battery and find one of these on the board, it has to be replaced.

(And even rechargable backup batteries, which could still be found on 486 boards, can fail & need to be replaced.)

[Robert M]

What is the message on the display screen after starting the computer if you do not use a diskette?

[Robert M]

Hey Dexahol,
Was recently re-reading this post and your second response.
Just to let you know......................................................
BIOS stands for Basic Input Output System ....not Built In Operating System.

[Zedy]

A lot of 486 boards that had battery integral with the RTC also had a pair of pins where an external battery could be connected using fly leads.
It is best to find out exact motherboard maker and model and do a search for some details to ensure you get it correct.

[Platypus]

Gee, this is an oldie popped up from nowhere.

[Dexahol]

Originally posted by Robert M
Hey Dexahol,
Was recently re-reading this post and your second response.
Just to let you know......................................................
BIOS stands for Basic Input Output System ....not Built In Operating System.

heh-heh . . . yup, you're right. In my defense, look at the time of my post.
I was probably still on my first cup-o-java.

Dex