Книга: Writing Windows WDM Device Drivers

Changing World

Changing World

Most programs that are used nowadays run using Win32 (or at least Win16) functions. These routines do not allow direct access to I/O ports, etc. For example, when keyboard input is required, W98 or W2000 carries out the necessary operation. In the IBM-compatible environment, it interacts with the keyboard controller using techniques dating from time immemorial.

Less DOS applications are being run. In W98, NT, and W2000, these do not get direct access to the hardware. Instead, a Virtual Device Driver arbitrates access to these peripherals, allowing multiple DOS and Windows applications to run at the same time.

These two developments allow the Windows operating systems to move away from the original IBM-compatible specification. As long as the right keystroke messages get through to user programs, it does not matter where in hardware they come from. For old DOS programs that do try to access the actual hardware, virtual device drivers on faster new machines can emulate the required functionality.

The new wisdom is that the USB and IEEE 1394 (originally called FireWire) devices represent an easier way for users to connect assorted peripherals to the system, including standard system components such as a keyboard and a mouse. The idea is that any devices can be plugged in easily (even when the computer is on) and — within limits — daisy chained together. USB and IEEE 1394 devices cope with being plugged in anywhere. The Windows Plug and Play system sorts out any resource allocations on the fly.

Whether users will take to the new doctrine remains to be seen. Plugging a new USB device in will certainly be easier than dismantling a case, fiddling with jumpers, and inserting a card. The new Device Bay specification will allow easy insertion of cards within the chassis of the PC.

USB's 12Mbs is designed for slower-speed devices, such as keyboards, mice, joysticks, printers, modems, telephones, and monitors. IEEE 1394 runs faster, at 100 Mbs or more, and is more useful for devices such as scanners, storage units, and audio/visual kit, such as digital cameras.

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