To provide the maximum level of hardware independence for OS/2 2.0,
device drivers are used to communicate with hardware devices. OS/2
2.0 makes use of two distinct types of device drivers for
communication with hardware devices:
- Physical Device Drivers
- Communicate directly with hardware devices.
They operate in protect mode and are
accessed by protect-mode processes and by
VDDs.
- Virtual Device Drivers
- Do not communicate directly with hardware
devices. Instead, they provide a virtual
device driver interface for DOS applications
running in DOS sessions. DOS applications
typically address hardware devices directly
using interrupts. The virtual device driver
allows the DOS environment to appear to the
DOS application as though the application
had direct control over the hardware.
For more information about VDDs, see "Virtual Device Drivers." A new
disk driver interface has been defined for use by the HPFS.
The following is a summary of the device driver changes from OS/2 1.x:
- The disk device driver records the information, indicating the
type of DASD (ESDI/ST506 or SCSI) and the level of caching support
for each logical drive (LID).
- Disk caching for FAT disk partitions is performed only for devices
where caching is not provided by the hardware.
- An additional set of request control functions is supported to
allow direct communication by the HPFS File System Driver (FSD).
Subsections