## Storage Device Driver Reference

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### Glossary - V

V

VBIOS - Virtual BIOS device driver

VCMOS - Virtual CMOS device driver

VDD - Virtual device driver

VDH - Virtual video Device Handler

VDM - Virtual DOS Machine; use DOS session.

VDMA - Virtual Direct Memory Access device driver

VDSK - Virtual hard DiSK device driver

video graphics adapter (VGA) - A computer adapter that provides high- resolution graphics and a total of 256 colors.

VIO - Virtual Input/Output

VIRR - Virtual Interrupt Request Register

Virtual Device Driver (VDD) - In the OS/2 operating system, a type of device driver used by DOS programs running in a DOS session to access devices, such as the screen or mouse, which must be shared with other processes in the system. The virtual device driver maps DOS device commands to the normal (physical) device driver under OS/2 2.0 and later versions of the operating system.

virtual DevHlp (VDH) - Kernel (linear memory, paging, hardware interrupt, event control, port control) services provided to virtual device drivers.

virtual I/O (VIO) - A facility that pages data into and out of external page storage.

virtual memory - Synonym for virtual storage.

Virtual Programmable Interrupt Controller - Virtualizes the 8259 Programmable Interrupt Controller (PIC). A special virtual device driver, in that it provides services to other virtual device drivers.

virtual storage - Addressable space that is apparent to the user as the processor storage space, from which the instructions and the data are mapped into the processor storage locations. Synonymous with virtual memory .

visible region - A window's presentation space clipped to the boundary of the window and the boundaries of any overlying window.

VPIC - Virtual Programmable Interrupt Controller device driver.

VRAM - Video Random-Access Memory.

VTIMER - Virtual TIMER device driver.

V86 mode - Virtual 8086 mode of the 80386 CPU.