Macs & Multiple Monitors

Originally published 25 October 2000 as a Mac Daniel article for Low End Mac.

Q: I have two (or more) monitors on my Mac. What's the best way to set them up?

A: If you have more than one monitor, using them on the same Mac can give you a lot more screen area without the need to invest in another, larger, more expensive monitor. Used Mac video cards, especially NuBus cards, are often available at minimal cost.

In general, I recommend setting up the highest-resolution monitor on the fastest video system and work your way down. The NuBus Video Card Profile section will tell you which cards are accelerated and which aren't. In most cases, acceleration is all about the same speed — somewhere in the neighbourhood of 2-3x built-in video speeds on a Power Macintosh 8100. (The Thunder IV GX cards from Radius, the Thunder II GX cards from SuperMac, and any other DSP-accelerated NuBus video cards are notable exceptions — they run even faster.)

The way most people do it, the largest, highest-bit-depth monitor is used for displaying large images, and the smallest, lowest-bit-depth monitor is used for toolbars, palettes, and possibly the main desktop (with the Mac menu bar, hard drive icon, and Trash). Intermediate monitors may be used for either purpose, depending on individual needs.

A quick rule of thumb that may help you out is to multiply the monitor size in inches by the bit depth you can use on it, which will approximate how much relative horsepower you'll need to drive that monitor. Rank your monitors like this and see how that works for you.

Case in point: I have a Mac IIci with a SuperMac Spectrum/24 Series IV card and a Macintosh Display Card 8•24 in it. I usually drive a Multiple Scan 15 at 832x624 in 24-bit colour with the SuperMac and an Apple 13" High-Resolution RGB monitor (640x480, 24-bit) with the 8•24, leaving the built-in video alone (see below for why). I occasionally use a Portrait Display on the built-in video as well. The SuperMac is the fastest card, so I use it for the highest-resolution/highest bit-depth monitor (15 inches x 24 bits gives me 360 relative horsepower units). The 8•24 is next, and I use it for the next highest bit-depth and next highest-resolution monitor (13 x 24 = 312). Finally, the built-in video is used for the Portrait (15 x 4 = 60).

I also have a Mac IIfx. I have, on occasion, used the SuperMac and 8•24 in it. I use the SuperMac to drive a Multiple Scan 15 at 832x624 in 24-bit colour for my graphics monitor (15 x 24 = 360) and the 8•24 to drive an Apple Two-Page Monochrome in 256 greys (21 x 8 = 168) for my menu bar and palette monitor. While the SuperMac is the faster card in this case, using its acceleration with greyscale video seems to be a bit wasteful. You really don't need acceleration or a colour display for the Finder and toolbars in PageMaker or Photoshop, so I put the Two-Page Display on the 8•24.

If you have a Mac IIci or IIsi, your video performance will be greatly improved by the addition of a video card, even if the card is unaccelerated. Due to the design of the video subsystem in these two machines, they both use the first 1 MB of system RAM for video RAM, which hurts both system and video performance. Putting a video card in will allow you to avoid the built-in video (or to use the built-in video to drive a palette monitor, which doesn't need 24-bit colour or acceleration), thus speeding up the machine.

With Macs that support the Portrait or Two-Page Display with internal video, you may wish to use the internal video to run that and your NuBus slots for the accelerated video cards, since an accelerated card will nearly always be substantially faster than internal video and the greyscale screens require less graphics horsepower.

If I had an accelerated video card with only 8-bit colour support (the Radius PrecisionColor 8-XJ, for example) and built-in video or an unaccelerated video card that supported 16- or 24-bit colour, the decision would be a bit tougher and would depend on what I would use the Mac for. If I were going to be doing a lot of work with photographic images, I would give up the acceleration for the greater bit depth. If I were going to be doing anything else (web browsing, for example), I would put the accelerated video card on my highest-resolution monitor and use the lesser video card(s) for the lower-resolution monitor(s).

Choosing a monitor setup is very much dependent on your personal work preferences, but these guidelines should help you in setting up your system.

copyright ©2000-2004 by Chris Lawson