Device Driver Basics

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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
which queries the hardware components and builds the
registery key
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

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

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

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

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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Stephen Bucaro