Macintosh Display Card 8•24 GC

The Macintosh Display Card 8•24 GC is an accelerated 12″ NuBus video card compatible with 68020– and 68030-based Macs. Acceleration is not available if the card is installed in a 68040-based Mac – in fact, the 8•24 GC control panel will bomb the computer.

Macintosh Display Card 8-24 GCThe card’s driver version 1.0 software is required to enable acceleration with System 6, and System 7.0-7.1 require driver version 7.0.1. The card’s drivers will not run under System 7.5 unless the Mac is in 24-bit addressing mode. Apple TIL Article #26094 notes some other incompatible applications.

The 8•24 GC is PowerPC-compatible – at least on a PPC-upgraded Mac IIci – under Mac OS versions from 7.6 to 8.6 with the ATI Graphics Accelerator Extension, available for download from Apple. It is unknown whether this works with System 7.5.x. Anyone with a Quadra or NuBus-based PPC in a position to try this is encouraged to do so and post in the comments.

Hands On

We tested an 8•24 GC Rev. A in a Mac IIfx, a IIci with cache card, a IIcx, and a Quadra 650. All were running System 7.5.5 on an external Quantum Fireball 2.1 GB hard drive. Each will run the card in 1-, 8-, and 24-bit modes without the 8•24GC control panel. We were only able to use the 640 x 480 setting with a ViewSonic V95 monitor, but that may be due to the Mac-to-VGA adapter in use.

The Mac IIci refused to boot with the 8•24 GC control panel installed, even if it was the only additional item in the System Folder. The Quadra did the same thing when set to 24-bit memory; with 32-bit memory enabled, the 8•24GC driver disabled itself as incompatible with the ‘040 processor.

The following video benchmarks were obtained at 640 x 480 resolution using Speedometer 4.02:

computer           1-bit  8-bit 24-bit
IIcx, "Toby"       0.252  0.248  n/a
IIcx, accelerated  0.421  0.422  n/a
IIci, int. video   0.467  0.461  n/a
IIci, no driver    0.385  0.385  0.385
IIfx, no driver    0.448  0.448  0.446
IIfx, accelerated  0.748  0.751  0.738
Quadra 650, int.   1.340  1.341 *1.334
Quadra 650, w/o    0.815  0.809  0.807
* Quadra 650 at 16-bit setting

The Mac IIcx doesn’t support 24-bit video with this card. The “Toby” card is Apple’s unaccelerated Macintosh II Video Card. The 8•24 GC accelerated performance 67-70% in these tests, making it nearly as fast in a IIcx as “Toby” in a IIfx or the internal video of the 25 MHz IIci.

The Mac IIfx runs the unaccelerated 8•24 GC about 16% faster than the Mac IIci, which is comparable to results for other unaccelerated video cards. However, the 8•24 GC runs two-thirds faster (165-168%) with the driver installed.

On the other hand, the onboard video on the Quadra 650 offers almost double the performance of the 8•24GC on the IIfx; it would not make a lot sense to add the card unless you need 24-bit video or are adding a second monitor. Even then, since the acceleration software doesn’t work with the Rev. A on a Quadra 650 running System 7.5.5 (the tested configuration), you would want to use internal video for your main monitor.

Of the many NuBus video cards tested, this is the fastest in the IIfx, so it is a good video card to use in the IIfx.


The 8•24 GC provides standard QuickDraw acceleration with the driver software installed.

  • 640 x 480 at 1, 2, 4, 8, and 24-bit color
  • 640 x 870 and 1152 x 870 at 1, 2, 4, and 8-bit color
  • Rev. B adds support for 832 x 624 resolution and 16-bit color
  • The 8•24 GC was originally designed for the “wicked fast” IIfx. The 8•24 GC can accelerate the performance of the Display Card 4•8 and 8•24 if installed in a system with either of these cards and acceleration enabled, due to their support of slave NuBus block transfers. (Other third-party NuBus cards may also support slave NuBus block transfers.)
  • If more than one 8•24 GC is installed in a system, only one can have its acceleration enabled.
  • The Rev. B ROM (ROM part number 341-0266 or 341-0812) is required for Macintosh 16″ Color Display 832 x 624 support.
  • The two RAM slots on the card can take paired, 80 ns or faster, 64-pin SIMMs of the same spec as those for the Macintosh IIfx. RAM can be upgraded by up to 8 MB (using two 4 MB chips) but any performance gain is very unlikely as most software will not utilize the full 10 MB of GWorld cache possible with this setup.
  • The 8•24 GC is often available on eBay for under US$30, though it isn’t always listed as an 8•24 GC card.

Further Reading

Keywords: #nubusvideo #acceleratedvideo