Classic Computer Magazine Archive COMPUTE! ISSUE 154 / JULY 1993 / PAGE 60

Where hardware meets software. (Basic Input/Output System or BIOS) (includes related information)
by Richard C. Leinecker

Today's computers think faster than mere mortals can comprehend.

But without software--the instructions the processor performs--a computer is just a pile of scrap iron, wire, and silicon.

Application software has to run on virtually an infinite variety of hardware configurations. That's why each IBM-compatible computer has a liaison layer that acts as a compatibility-assurance arbitrator between the application software and the hardware. This layer is called the BIOS (Basic Input/Output System). It usually resides in two ROM chips on a computer's motherboard.

Imagine the difficulty software developers would face if they had to worry about whether their products were saving data to a 20MB or a 200MB hard drive. They'd need to treat each variation as a different case. Or worse yet, what if they had the additional difficulty of providing separate routines to deal with each drive type, whether it was an IDE, MFM, SCSI, or RLL drive? If not for the BIOS, applications would be many times larger than they are. The BIOS shields developers from these headaches by providing a standard way of talking to hard drives and other hardware.

There's a standard way of dealing with all peripherals, including floppy and hard drives, modems and serial ports, printers, video systems, and keyboards. DOS (the Disk Operating System) builds its own routines around the BIOS routines. That's why different versions of DOS run on all IBM-compatible systems.

Some peripherals, like video cards, have their own embedded BIOS. In most cases the specialty BIOSs add functions that extend the original BIOS. A good example is a VESA-compatible (Video Electronics Standards Association) Super VGA card. At runtime the video card patches the base BIOS so that new routines are available to application software. This is necessary because video standards change rapidly and many people upgrade their video systems many times before replacing their computers. The motherboard manufacturer couldn't possibly anticipate which of the hundreds of types of video boards users will install.

In addition to allowing the operating system to communicate with the hardware, the system BIOS also contains diagnostic programs that check out the computer each time it's turned on. This series of diagnostic tests is called the POST, or Power-On Self Test, and it involves checking the microprocessor, memory, video system, and other internals. Not all installed options are tested. For example, printers and modems are not tested.

The more comprehensive the POST, the better your computer can diagnose itself and alert you to problems. And the more memory you have installed, the longer the tests take to verify it all.

BIOSs Aren't Created Equal

IBM was the creator of the first BIOS used in a PC, but it was the development of third-party BIOSs that made it possible for virtually anyone to build a PC. The three major companies that specialize in development and sales of compatible BIOS products are AMI (American Megatrends, Incorporated), Award Software, and Phoenix Technologies. Each one licenses its BIOS to hardware manufacturers. Selecting a BIOS for motherboards isn't easy. A list of questions has to be addressed in order to choose a BIOS that's already been designed or to custom-develop a BIOS.

The AMI BIOS has a built-in setup program activated by pressing the Delete key in the first few seconds after the boot procedure begins. In addition to the setup program, the AMI BIOS Features a built-in, menu-driven diagnostics package.

The Award BIOS has a built-in setup program activated by pressing Ctrl-Alt-Esc. Award is unique among BIOS manufacturers in that it provides its code to hardware manufacturers and allows them to customize the BIOS themselves. Because of this customization, the hardware companies can fine-tune the BIOS to work best with their computers.

The Phoenix BIOS has been the standard by which others are judged. It was the first third-party BIOS on the market. One area of particular strength for the Phoenix is its POST. The BIOS outputs an extensive set of beep codes that help diagnose problems on the motherboard. It can even isolate a memory failure to an individual chip. This simplifies identifying system problems for the owner or the repairperson.

If you have a modem, you can get support from these BIOS manufacturers (or their distributors) or from their BBSs (see the "Support Reference" sidebar). All of these BIOSs have been on the market for years. Although they offer different kinds of diagnostics, all are extremely reliable and have proved themselves over time. But since they have to be updated every time a new piece of hardware is introduced, a few bugs have cropped up from time to time.


Like all software, the ROM BIOS is not immune to bugs. If your BIOS is from one of the major manufacturers, you're probably safe. But even then, don't forget that BIOS manufacturers have had some minor problems.

How can you protect yourself from problems when you're buying new and used equipment? If you're considering the purchase of used equipment, you should install the applications you'll be using and make sure they perform the way you expect before laying your money down. For new equipment, you should install your applications and put them through their paces as soon as you can. If you find a problem, contact the source that sold you the computer.

BIOS Upgrading

You'll rarely be in the position of needing a BIOS upgrade. Here's a list of reasons why you might want to consider it.

* Adding support for 720K 3 1/2-inch, 1.2MB 5 1/4-inch, and 1.44MB 3 1/2-inch drives.

* Allowing a user-definable hard drive type that matches an MFM, RLL, IDE, or ESDI drive.

* Adding support for 101-key enhanced keyboards.

* Correcting known conflicts or buts. It's best if you contact the hardware or software vendor's technical support to verify that there is a problem with your particular BIOS.

* Adding features and performance found in newer BIOS versions.

Before you go shopping, you'll need some information.

* Make and model of the system. For many popular systems this is all that's needed to find the right BIOS. For less common clones you'll need more information.

* The CPU type (286, 386SX, 386, 486SX, 7486).

* The make and version of the existing BIOS. This is necessary because some revisions will require that the keyboard controller be replaced, too.

* The type and number of the existing BIOS ROMs. Locate the part number of one of the ROM chips. You may have to peel back a label. The part number will usually start with 27.

* Check for an integrated chip set. This will consist of square, flat, large-scale integration chips with pins around all four sides. They'll usually have a manufacturer's name or logo. Some examples are CHIPS, SUNTAC, VLSI, and OPTI. An integrated chip set performs the functions of hundreds of smaller chips. Even IBM uses third-party integrated chip sets on some models.

To get this information, open your computer's case and start taking notes. It only takes a few minutes. With this information you can accurately order BIOS upgrades.

There are some alternatives to upgrading your BIOS. Some companies (Washburn & Company, for example) supply accessory ROMs to augment the existing BIOS. They can fit in the two empty sockets that are found on most AT motherboards, or they can go on a card that fits in any 8- or 16-bit slot.

If you've identified a specific problem, some technicians are well versed at patching BIOSs. But it may be risky if the person doing it doesn't possess the skills. (I don't think I've ever heard a technician admit he or she couldn't do something until it was too late.) Unless you have complete confidence in a technician, leave this option out.

Don't Be Fooled by Imitations

Just because your computer boots and shows you the copyright of a major BIOS manufacturer doesn't mean you're home free. If you bought your system used, bought it from a cut-rate source, or have had it serviced by cut-rate technicians, there's a small chance you have an illegal BIOS copy. I've heard of more than one person who, having experienced system-level bugs and incompatibilities, inspected the motherboard and found a BIOS copy--not the real thing.

This is illegal and dilutes the BIOS manufacturer's ability to provide the best possible product for paying customers. Besides that, those BIOS copies may not be the best fit for the systems.

It's pretty easy to distinguish the real McCoy from a fake. Take a look at the ROM BIOS chips on the motherboard. You should clearly see the name of the manufacturer, along with a serial number, usually on a label. If you buy a new system with a fake, report the supplier to the manufacturer of the BIOS cloned on the fake chips, and return the system for a full refund. If you're looking at a used system with a copied BIOS, tell the seller you're not interested. Even if you buy it at a bargain price, you're in for trouble in the future.

Into the Sunset

Most people never consider the BIOS version and manufacturer when purchasing a computer. We take it for granted that such an integral component is carefully checked by the system manufacturer for correct operation, and it almost always is. But as a system ages and newer peripherals become available, you need to be thinking about a BIOS upgrade to support newer hardware. Generally, a BIOS upgrade is a step involved in some other kind of major equipment upgrade. If you install the hardware correctly and it still won't work, your BIOS automatically becomes the prime suspect.

The guidelines I've presented should help you make your purchase and upgrade decisions now and in the future. If you have any questions, though, a reputable technician will help you out. And if you're adventurous and want to upgrade, order the chips yourself and have at it.