Device Driver Basics

by: Stephen Bucaro

Most people understand that the "hardware" part of their computer is the real physical parts, like the keyboard, mouse, modem, hard drive and so on. They understand that the "software" is computer bits stored on the hard drive, CD-ROM, or other storage media. But most people are a little hazy about exactly what a "driver" is.

In this article, I'm going to reveal in plain English what a driver is, why we need drivers, and exactly where the drivers are hiding. To give you a basic understanding, I'm going to go back, way back, to the early days of computers.

The Early Days

The year is 1981 and the world is in the midst of a severe resession. IBM's main frame business has slowed and the company is losing money. Up until now they had been laughing at the array of microcomputers on the market: Atari, Commodore, sinclair. Toys really, mostly used to play computer games.

The problem was, these "toys" were selling like hot cakes. IBM had to get into that market and get into it fast. They didn't have time to design and build a computer complete enough to compete in the market, so they built an "open system". They used commonly available electronic components and they published every design detail (including the code), and they even provided plug in slots so that others could build components for their computer.

And people did provide components for the IBM PC. They provided video cards, memory expansion cards, input-output port cards, game port cards, hard disk interface cards, and much more. How were all these various devices able to interface with the PC's operating system? That's where a "driver" comes in.

A hardware device is constructed with various electronic components using various control signals, but the software interface to the operating system is standardized. A device's interface to the operating system must follow the interface specification. A driver is a piece of software that translates the hardware's control signals to signals that the operating system expects, and translates signals from the operating system to the hardware's control signals.

When the computer is started up, it would look in the "system" directory for files with the extension ".drv" and load them into memory. Specific files like autoexec.bat, config.sys, and win.ini were used to inform the operating system about drivers. Hardware would be configured through these files, or through jumpers located on the device itself.

The driver specification evolved along with the PC. Today when a PC starts, it executes the program ntdetect.com which queries the hardware components and builds the registery key:
HKEY_LOCAL_MACHINE\HARDWARE\SYSTEM\CurrentControlSet.
This key exists only in memory and is created each time the computer boots. If all the drivers are loaded successfully, a copy of the key is saved as ControlSet00X.

Under the registery key CurrentControlSet, the subkey "Enum" contains a subkey for each harware device on the computer. Each device key contains fields for Hardware ID, Driver ID, Device Parameters, and other configuration data. The 32-bit drivers are files with the extension ".sys" and can be found in the folder C:/winnt/system32.

Driver Signing

Microsoft has been the brunt of much criticism because of the poor reliability of the Windows Operating System. I feel that much of this criticism is justified. On the other hand, as I described in part 1 of this article, the PC was designed by IBM as an "open" system. Anyone can sell a hardware device (or software) for the PC. Should Microsoft be held responsible for the quality from a third-party?

As I described in Part 1 of this article, the operating system doesn't interface directly to a hardware device. There is a piece of software called a "driver" that translates the hardware's control signals to signals that the operating system expects, and translates signals from operating system to the hardware's control signals. Obviously, the hardware manufacturer provides the driver.

Because the driver works between the operating system and the hardware, a bug in the driver can cause a serious problem. Many of the problems with Windows have come from bugs in third-party drivers that Microsoft had nothing to do with. For this reason, Microsoft created a Hardware Quality Lab to test drivers. A hardware manufacturer can submit their driver for testing, and if it is passes rigorous compatibility testing, it receives Microsoft's digital signature.

You may have received a message during the installation of a hardware device warning that the driver was not signed. Why would a hardware manufacturer fail to have their driver certified by Microsoft? The computer hardware market is very competitive and the manufacturer might want to bring a new product to market before thorough testing can be completed. Or maybe they don't want to or can't afford to pay Microsoft for certification. The question is, should you click on the "Continue" button to install the unsigned driver?

In my experience, I have never been able to trace a problem to an unsigned driver. If it's your home computer and you performed a back-up recently, go ahead and install the unsigned driver. If it's a computer on a corporate network, you may want to back-out of the installation and see if you can locate a signed driver first. Many times a manufacturer will release a product with an unsigned driver, then later provide a signed driver as a free download from their website.

If you decide to go ahead and install an unsigned driver, you can always update the driver later. If your computer works with the unsigned driver, I would not update the driver. When it comes to updating drivers (or the computers BIOS) I go by the old saying, "if it ain't broke don't fix it".

To update a driver, select Start | Settings | Control Panel and double-click on the "System Properties" Utility. In the "System Properties" Utility, select the "Hardware" tab and click on the "Device Manager" button. In the "Device Manager" window, right-click on the device in the list and select "Properties" in the popup menu. In the "Properties" dialog box, select the driver tab and click on the "Update Driver..." button.

In the "Properties" dialog box driver tab, you may have noticed the "Roll Back Driver" button. If your computer has problems with the new drive, you can click on the "Roll Back Driver" button to roll back to the previous the driver. Driver roll back saves only one previous driver, so if you update a driver, then update it again, the original driver is gone. If the computer has problems with the new driver, always roll back to the original driver before trying a different one. That way you'll always have the original driver to roll back to.

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About The Author
Stephen Bucaro
To learn how to maintain your computer and use it more effectively to design a Web site and make money on the Web visit bucarotechelp.com To subscribe to Bucaro TecHelp Newsletter visit http://bucarotechelp.com/search/000800.asp