Electronic wifi technology

VCPI is a good standard for DOS multi-taskers such as DESQview because in this situation there are many real mode programs being run but only two protected mode programs-the EMM and the multi-tasker, i.e. QEMM 386 and DESQview itself. However, VCPI fails when you move to the more complex requirements of a full protected mode multi-tasking system such as Windows 3. In this case it is possible for a number of real mode applications and a number of protected mode applications to be running at the same time and this goes beyond what VCPI was designed to control.

To solve these problems Microsoft introduced the DOS Protected Mode Interface or DPMI. The first version was included as part of Windows 3.0 and appeared isolated in the sense that Windows 3.0 was the only product to support it! DPMI isn’t VCPI compatible and all VCPI DOS extenders and EMMs immediately refused to work with Windows 3.0 However, the success of Windows 3.0 was so complete that within a few months nearly all DOS extenders and EMMs were reissued in DPMI compatible versions. This change was made without removing the VCPI compatibility and now most EMMs claim to be VCPI, DPMI and XMS compliant.

DPMI was extended to produce version 1.0 and this was incorporated into Windows 3.1 to produce a standard that looks set to survive for some time