Microsoft Windows - Computer Busses - page 551

• Support for user-specific information - the registry allows the storage of user-specific in-

formation, using the Hkey_Users key. This allows each user of a specific computer (or a
networked computer) to have their own user-specific information. INI files do not sup-
port this.

• Remote administration and system policies - the registry can be used to remotely admin-

ister and set system policies (which are stored as registry values). These can be
downloaded from a central server each time a new user logs on.

Figure H.2 shows an example of the registry in Windows 95/98.

Figure H.2 Example registry

H.3 Device drivers

In Windows 3. x , device drivers were complex entities and were, in part, static and unchang-
ing. Windows 95/98/NT now provide enhanced support for hardware devices and peripherals
including disk devices. Windows NT will be discussed in Section H.10. Windows 95/98 uses
a universal driver/mini-driver architecture that makes writing device-specific code much eas-
ier.
The universal driver provides for most of the code for a specific class of device (such as
for printers or mice) and the mini-driver is a relatively small and simple driver that provides
additional information for the hardware.
The actual system interface to the hardware (or some software parts) is through a virtual
device driver (VxD), which is a 32-bit, protected-mode driver. These keep track of the state
of the device for each application and ensure that the device is in the correct state whenever
an application continues. This allows for multitasking programming and also for multi-
access for a single device. VxD files also support hardware emulation, such as in the case of
the MS-DOS device driver, where any calls to the PC hardware can be handled by the device
driver and not by the physical hardware. Typical VxD drivers are:

EISA.VXD EISA bus driver ISAPNP.VXD ISA plug-and-play

SERIAL.VXD Serial port LPTENUM.VXD Parallel port

MSMOUSE.VXD MS Mouse PARALINK.VXD Parallel port

PCI.VXD PCI QC117.VXD Tape backup

IRCOMM.VXD Infra-red comms UNIMODEM.VXD Modem

WSOCK.VXD WinSock LPT.VXD LPT