On 10 Jul 2000, at 21:30, Frank R. Brown wrote: > I agree with your comment about the vdm. But what limitation > in dos/windows would prevent multiple vdm's from running? > nt has permitted multiple vdm's since its early versions. For win95 to be sucessful, MS had to ensure maximum compatibility with older apps and the ability to run on limited hardware (4 MB of RAM etc). A robust VDM mechanism breaks both these requirements. > I've never understood the complete story. But if dos/windows > has complete pre-emptive multitasking, how can a single rogue > app consistently hang the whole os? (In nt, this *rarely* happens There is a big difference in OS architecture. For example, on win9x, the running application thread has access to the memory space used by the system VM. On NT, what appears to the application as the ring 3 system DLLs are in fact just proxy stub forwarders (which pass the calls to the separate, isolated system VM). This is one of the reasons why on NT you don't have the OS crashes, lockups etc that you get with win98/95. There are other vulnerabilities, such as the 16 bit GDI code in win9x that allow a single app to hang the system. Gerard R Thomas Port of Spain, Trinidad and Tobago mailto:[log in to unmask] mailto:[log in to unmask] PGP Key IDs: RSA:0x9DBCDE7D DH/DSS:0xFF7155A2 PCBUILD's List Owner's: Bob Wright<[log in to unmask]> Drew Dunn<[log in to unmask]>