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PCs technically supported multiple displays earlier than that, it just wasn't something the VGA standard provided for. It was either a specialized expensive thi

PCs technically supported multiple displays earlier than that, it just wasn't something the VGA standard provided for. It was either a specialized expensive thing, or a mixing of standard graphics adapters occupying different IO ports. The Hercules graphics card [1] was popular for this application, since it could happily coexist with a VGA card. [1] https://en.wikipedia.org/wiki/Hercules_Graphics_Card#Hercules https://en.wikipedia.org/wiki/Hercules_Graphics_Card#Hercule...

Someone 8y ago
Hercules cards were extremely useful, but in the case of PCs, support meant little more than “if you plug in a card, the hardware will provide it power”. That worked if the cards didn’t happen to fight over who owned which interrupt or which memory region. It was up to individual applications to detect the presence of the cards and to write to them. In contrast, the Mac II supported multiple displays in the sense that QuickDraw would happily draw graphics across monitors, switching color depths along the way, without applications needing to even be aware of the presence of multiple graphics cards. The Mac also supported having multiple identical graphics cards plugged in. In contrast, a Hercules card could coexist with a VGA card, but not with a second Hercules card, for example.
- newnewpdro 8y ago
  You're imagining the fighting of resource ownership issue. VGAs don't even use an interrupt line. It was a simple matter of the Hercules emulating an MDA which had a distinct IO space from VGA/EGA. So you could just slap a Hercules card into a VGA machine and start running software that supported the combination. I don't know anything about Macs but I have no trouble believing it was superior. The PC was incredibly primitive in this area. But that's also why there was essentially nothing to configure when you inserted a VGA and Hercules card into a machine. Their physical configuration is defined by their respective standards, and the standard didn't consider multi-monitor support. It's just fortuitous that Hercules/MDA and VGA standards didn't collide.
jacobush 8y ago
I even got my Hercules running in Linux! But could not get Linux to switch consoles from VGA to Hercules and back without blanking the inactive monitor. :-/ My solution was to write little C programs which addressed the Hercules screen directly. Fun times! :) It was dog slow, even slower than in DOS.

Someone 8y ago

Hercules cards were extremely useful, but in the case of PCs, support meant little more than “if you plug in a card, the hardware will provide it power”. That worked if the cards didn’t happen to fight over who owned which interrupt or which memory region. It was up to individual applications to detect the presence of the cards and to write to them. In contrast, the Mac II supported multiple displays in the sense that QuickDraw would happily draw graphics across monitors, switching color depths along the way, without applications needing to even be aware of the presence of multiple graphics cards. The Mac also supported having multiple identical graphics cards plugged in. In contrast, a Hercules card could coexist with a VGA card, but not with a second Hercules card, for example.

newnewpdro 8y ago
You're imagining the fighting of resource ownership issue. VGAs don't even use an interrupt line. It was a simple matter of the Hercules emulating an MDA which had a distinct IO space from VGA/EGA. So you could just slap a Hercules card into a VGA machine and start running software that supported the combination. I don't know anything about Macs but I have no trouble believing it was superior. The PC was incredibly primitive in this area. But that's also why there was essentially nothing to configure when you inserted a VGA and Hercules card into a machine. Their physical configuration is defined by their respective standards, and the standard didn't consider multi-monitor support. It's just fortuitous that Hercules/MDA and VGA standards didn't collide.

jacobush 8y ago

I even got my Hercules running in Linux! But could not get Linux to switch consoles from VGA to Hercules and back without blanking the inactive monitor. :-/ My solution was to write little C programs which addressed the Hercules screen directly. Fun times! :) It was dog slow, even slower than in DOS.