发信人: ikoo()
整理人: simonshium(1999-06-30 20:17:20), 站内信件
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WHAT IS A VIRTUAL DEVICE?
A virtual device is a 32-bit executable that manages a system resource, such
as a hardware device or installed software, so that more than one application
can use the resource at the same time. Windows usese virtual devices to allow
multitasking for Windows-based applications. The virtual devices work in
conjunction with Windows to process interrupts, and carry out I/O operations for
a given application without disrupting the execution of other applications.
Most virtual devices manage a hardware device, and many also manage or replace
sorresponding software such as ROM BIOS routines. A virtual device can contain
the other software to carry out these operatins. In all cases, the virtual device
keeps track of the state of the device for each application, and ensures that
the device is in the correct state whenever an application continues execution.
Some virtual devices manage only installed software, such as an MS-DOS device
driver or a TSR program. Such virtual devices often contain code that
either emulates the software or ensures that the software uses data that applies
only to the currently running application. Virtual devices are sometimes used to
improve the performance of installed software; the Intel-compatible
microprocessors can execute the 32-bit code of a virtual device more efficiently
than the 16-bit code of an MS-DOS device driver or TSR.
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