Foreground sessions are even more useful on Dual Monitor systems, like the one below, because each session has exclusive access to an entire screen.
Use SHIFT-TAB to switch to the Color Display, press SPACE to start DONKEY,
and appreciate how well an IBM PC could actually run two programs simultaneously.
There’s also a “Dueling Monitors” demo featuring FOUR active sessions (two per monitor). This may be pushing the IBM PC a bit too far, but any session that’s waiting for input has no impact on performance.
It’s important to note that BASIC-DOS is not attempting to emulate a “virtual machine” within each session. That would require swapping global memory (eg, ROM BIOS Data) on every context-switch, which would be error-prone and slow. And it’s completely unnecessary, as long as BASIC-DOS apps rely exclusively on BASIC-DOS APIs. Realistically, ROM BIOS APIs and data should only be used by BASIC-DOS itself (ie, BASIC-DOS device drivers).
Even though in selected demos I will sometimes run PC DOS applications like MSBASIC, the fact that they work is a happy coincidence. Most actually do not work, either because they 1) use interfaces that BASIC-DOS has not yet implemented (and may never implement), 2) use BIOS interfaces that only BASIC-DOS should be using, or 3) have a stack so small that crashing is inevitable.
The fact that MSBASIC works at all, despite the fact that it’s “breaking the rules” and accessing the BIOS and hardware directly, is just another happy coincidence. By no means is it working perfectly. For example, if you type CTRL-BREAK while the Monochrome Display has focus, MSBASIC will intercept it, because it’s relying on the BIOS rather than BASIC-DOS “hot key” notifications.
The “stack” issue is another major difference between BASIC-DOS and PC DOS. BASIC-DOS never switches stacks within a session. The BASIC-DOS philosophy is simple: BASIC-DOS APIs should be re-entrant and apps should provide as much stack space as their calls require. PC DOS, by contrast, evolved complicated stack switching procedures and re-entrancy rules that slowed the operating system down, wasted memory, and were generally painful.
Let’s just say that BASIC-DOS will never support a STACKS keyword in CONFIG.SYS.
That’s the end of the current preview. All the demos featured in the preview are also available in our set of Demo Configurations.
Copyright (c) 2020-2021 Jeff Parsons Released under MIT License