vertical scan frequency
The number of times an entire display screen is refreshed, or redrawn, per second. Measured in Hertz, display systems range from 45 to over 100Hz. For example, VGA in the U.S. is generally 56 to 60Hz; in Europe, 70Hz and above. TV is refreshed 60 half-frames/sec (interlaced) resulting in 30 full frames/sec. Contrast with horizontal scan frequency.

VFAT
(Virtual File Allocation Table) A file system used in Windows for Workgroups and Windows 95. It provides higher-speed, 32-bit Protected Mode access for file manipulation. It also supports file names up to 255 characters in length compared to DOS' 8.3 file names (name-8, extension-3).


VxD
(Virtual Device Driver) A special type of Windows driver that allows Windows to perform functions that cannot be done by applications communicating with Windows in the normal manner. VxDs run at the most priviledged CPU mode (ring 0) and allow low-level interaction with the hardware and internal Windows functions, such as memory management.
Like DOS TSRs, poorly-written VxDs can conflict and lock up the system. WIN386.EXE (Win 3.1) and VMM32.VXD (Win 95) are the VxD files that provide the primary functions (kernel) in Windows.


Glossary Index

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