Based on Xerox Parc work and predating the Mac -although the Lisa may have had some influence. Dialog boxes and the dialog processing loop have to be done from scratch. Low level operations are done via DOS interrupts. Debugging requires a second monitor and graphics card. Windows 2.0 Windows can now overlap.
Dialog boxes are now easier because of built in support for dialog box creation and processing.
Excel includes a cut down copy of Windows, as the market penetration is still tiny. By Charles Petzold. Programmers can now write programs which work. Microsoft support help you with programming problems without asking for a credit card. The origin for drawing is the bottom left corner.