| MCSE Core Technologies Exam: NT 4.0 Architecutre Compiled by Amos Satterlee |
| Win 16: Windows-on-Windows (WOW) back to Diagram back to Introduction/TOC |
The 16-bit applications multi-task cooperatively within a VDM. This means that if one crashes, all crash. To prevent such situations, it is possible to start each 16-ap in its own VDM. An added benefit is that each VDM multi-tasks pre-emptively. Running multiple VDM's will take up significantly more memory than running all the aps in one VDM. The trade-off is that, when run in separate VDM's, if one ap crashes, is does not crash all the rest. This should probably be reserved for critical applications. To start a 16-bit application in its own VDM, right click on the program shortcut and go to Properties. At the shortcut tab, select Run in Separate Memory Space. In a multi-processing system, be aware that NT will not multi-task a VDM across multiple processors. However, if more than one VDM is running, then each one can be assigned to a different processor. There is no way to change the priority level of a 16-bit ap. The cooperative multi-tasking design does not provide for direct communication with the operating system. Under NT, it is possible to change the priority level of the VDM running the 16-bit application(s). Some 16-bit aps, especially those that make direct calls to the hardware, will not run under NT. |