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Post by juju on Mar 7, 2006 13:55:24 GMT -5
When referring to a computer, a device is a hardware unit that extends or assists the existence of the computer in some way. Except for the motherboard, the processor, and the memory (RAM), everything that connects to the computer in some way is considered a device. Keyboards, printers, scanners, monitors, serial ports, disk drives, and microphones are all examples of devices. The word "peripheral" is often used as a synonym for device.
Unfortunately, most of the devices connected to your system don't speak the same language as the computer. Device drivers, or simply drivers, are programs that act as translators between the device (a joystick, for example) and the application using that device (such as a computer game). Drivers can translate information from a device, such as a microphone, or they can translate information to a device, as in the case of a printer. Essential devices, such as the keyboard, that are necessary to simply operate the computer, are loaded during the boot process or in the system's BIOS (Basic Input/Output System).
OSes (operating systems), such as Windows, are published with many device drivers. If all devices are connected, Windows should recognize them and install the appropriate driver. When Windows can't recognize a device it will ask the user to find the driver. Today, all devices sold come with drivers on floppy diskette or CD-ROM. If you don't have a disk, you can find drivers on the manufacturer's Web site usually in the "downloads" section of the support area. Often these downloads and disks have executables that will automatically install the drivers. If not, run the Add New Hardware utility in the Control Panel. At one point, the wizard will ask you to point to the drive and directory where the drivers can be found. The driver will have the extension .DRV or .VXD.
The answer to many computer problems frequently is corrupted or outdated drivers. If your monitor doesn't display properly or your printer spits out multiple pages with garbage characters, chances are you need to update the driver.
Before Windows, applications that ran in DOS often required their own drivers. Drivers weren't always installed by the operating system. Many had to be installed by applications. For example, in DOS each word processing application would have to write printer drivers for every single printer manufactured. When the PC evolved to Windows, users and developers were elated because every application could use the one printer driver installed by the OS.
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Post by juju on Mar 7, 2006 14:17:44 GMT -5
device driver interface (DDI)
The communication between peripheral hardware (such as printers, external drives, and digital cameras) and a PC via software known as a device driver.
peripheral
Printers, modems, disk drives, scanners . . . anything short of the pencil sharpener that takes up space on or near your computer desk is likely a peripheral. Technically, a peripheral is any device that is not part of the essential core operations of the main computer, which is just about anything that isn’t part of the processor, memory, or anything that deals with data path transactions, which enter or receive data when interacting with the main computer.
Sometimes these extraneous devices sit inside the computer case or tower, much like an internal modem or CD-ROM drive. Other peripheral devices, such as printers or flatbed scanners, are found outside the computer. Just because a device isn’t located outside the computer case does not mean it isn’t a peripheral. Peripherals can also be called I/O (input/output) devices. In all instances, the peripheral must be connected to the computer either with a wired or wireless connection called a bus. Thus, a PCI (Peripheral Component Interconnect) bus or a USB (Universal Serial Bus) is used to connect peripherals to your computer.
USB is the current standard because it surpassed the speed and multiple platform flexibility of PCI. Up until the late 1990s, however, peripherals relied on PCI standards for connecting and communicating with the main computer.
PCI was a development of Intel in 1993. At that point, the standard was the most common way for desktop machines to communicate with external apparatuses. For about five years, PCI was the standard path toward connectivity.
To better understand PCI, find an older computer running older peripherals and take a look at the plug that connects the peripheral to the computer. If it’s long and flat with a row of small pins inside and a slightly spongy inner layer, it’s PCI. PCI connects a peripheral to a computer at speeds of about 20MHz to 33MHz and transmits 32 bits at a time in a 124-pin standard connection, though it can expand to transmit 64 bits in a 188-pin connection. Most computers come standard with three or four slots, or plugs, that will accommodate just as many peripherals. However, adding more expansion slots is possible.
For its day, PCI was revolutionary because it allowed for faster action and reaction between peripherals and because it replaced the ISA (Industry Standard Architecture) standard with its user-friendly plug-and-play capability that automatically configured at startup. PCI used all active paths to transmit both address and data signals, sending the address on one clock cycle and data on the next, thus allowing for faster performance from whatever peripheral it is connected to.
driver distraction
Driver distraction can refer to anything that diverts a driver’s attention. Eating, drinking, or changing the radio channel are possible forms of driver distraction. The form the wireless industry is most concerned with is distractions caused by wireless phones. Wireless companies have launched PR campaigns to address the issue and promote safe use of mobile phones while driving.
input driver
A short program or portion of a program that directs communication between a peripheral device and the CPU.
line driver
A device that boosts the strength of a signal before sending it down a line. A line driver increases the transmission distance, which helps to ensure the signal reaches its destination.
mouse driver
A program that lets a computer communicate with a mouse
network device driver
The software, usually distributed by the manufacturer, that lets a specific network card communicate with the rest of the computer system and the network.
printer driver
A program that lets a PC communicate with the printer. A printer driver will translate commands from the computer into instructions the printer understands.
virtual device driver (VxD)
The Microsoft Windows OS (operating system) uses VxDs to help create its multitasking environment where different applications and hardware devices can work together to accomplish several tasks simultaneously. Regular device drivers are small programs that help a hardware device communicate with the computer. VxDs are actually individual programs or files assigned to each of the computer’s main hardware devices, including the hard drive controller, keyboard, modem, printer, serial and parallel ports, and more. Therefore, VxDs essentially act as device drivers for the computer’s OS to help it manage multiple requests for the same hardware resource, imitate the presence of actual hardware, and perform other core functions.
VxDs handle the memory requirements of system devices so that conflicts do not occur when more than one application accesses the same device. They also deal with software interrupts from the OS. (A software interrupt occurs when an application terminates or requests certain services from the OS.)
The acronym “VxD” actually stands for virtual “something” driver, where the wildcard “something” represents one of the devices of a computer system. For instance, VmD might be the name of the virtual mouse driver. You’ll find VxDs referenced in Windows’ System.ini file under a section titled [386Enh]. If a driver uses the .386 file extension, you know that driver is actually in another file (such as Device=vmd.386). On the other hand, if the .386 file extension is replaced with an asterisk (for example, Device=vmd.*), then the driver is part of the Windows Enhanced mode kernel.
Windows Driver Model
A standard used by Microsoft that allows IHVs (independent hardware vendors) to write one driver for their hardware that works with both Windows 98 and Windows NT.
Windows Driver Model (WDM)
To understand why the Windows Driver Model makes sense, we first need to know what a “driver” is. To put it as simply as possible, drivers are small software programs, usually written by the manufacturers of hardware devices (such as printers, scanners, mice and other pointers, specialized keyboards, digital cameras, and many other peripheral devices). The purpose of the driver is to translate what you are doing with the computer into instructions that the peripheral hardware device understands so that, for example, the document you send to your printer comes out looking the way you expected instead of being undecipherable gobbledygook.
Clever, well-written drivers can make your use of peripheral devices efficient, fast, and satisfying. Poorly written drivers can make you crazy, particularly when they fight with the OS (operating system) or introduce incompatibilities with other software.
Drivers are not a Windows phenomenon. There have been drivers for as long as there have been computers with external (and sometimes internal) devices attached to them. In the days of character-based DOS (such as MS-DOS, the Disk Operating System produced by Microsoft; PC-DOS from IBM; and DR-DOS from Digital Research), driver coordination could be a nightmare. Every application had to ship with compatible drivers for mainstream devices. Hardware devices tried to ship multiple drivers for multiple applications. At one point, for example, the DOS-based versions of WordPerfect shipped with several hundred drivers for printers, while new printers might ship with multiple drivers for WordPerfect, Word, WordStar, and so on.
The result was that consumers were constantly walking a tightrope. If you upgraded your printer or your application software (if you got a new version of your favorite spreadsheet application, for example), you might suddenly discover you could no longer print reliably and that installation of a new driver from company A’s product B suddenly interfered with all other software on your computer.
With the introduction of the Windows Driver Model, many (although not all) of the problems created in this environment went away. The idea was that the manufacturers of hardware could write one driver that was supposed to work with instructions received from Windows and not from individual programs. In the meantime, software publishers could also work toward one driver that sent instructions to the OS (Windows) and not to individual hardware devices.
Of course, this system isn’t without flaws. There are still multiple OSes that manufacturers have to work with, including multiple versions of Windows, Linux, Unix, the Mac OS, Solaris, FreeBSD, and the more or less obsolete OS/2 and DOS. So it goes. All the while, Windows keeps changing, too; each time it does, it often means hardware drivers have to be rewritten.
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