Jump to content

Apple 8•24 GC Card

From RetroTechCollection
Apple Macintosh Display Card 8•24 GC
The 8•24 GC in Apple's 1994 module identification manual, with the DRAM SIMM sockets, ROM and RAM DAC marked
Manufacturer Apple Computer
Type Accelerated 24-bit NuBus display card
Release date 1990
Interface NuBus, DB-15 video connector
Compatible Macintosh II family computers with a NuBus slot
Power 20 W (maximum)
Part number 661-0606 (Rev. A), 661-1642 (Rev. B)

The Apple Macintosh Display Card 8•24 GC is a NuBus display card for the Macintosh II family that adds a graphics coprocessor to the display circuitry of the Display Card 8•24. An AMD Am29000 RISC processor at 30 MHz runs a version of 32-Bit QuickDraw on the card, and Apple quoted drawing 5 to 30 times faster than standard 32-Bit QuickDraw.[1][2][3] It appeared in 1990 alongside the 4•8 and 8•24, and Apple's develop journal described its design for programmers.[4][2]

The display side matches the 8•24: same connector, pinout, signals, sense codes, interlaced output and convolution. The Apple Display Card 8•24 page covers those in full.[5][2]

Specifications

[edit | edit source]
Macintosh Display Card 8•24 GC
Item Specification
Coprocessor AMD Am29000 RISC, 30 MHz
Video RAM 2 MB, soldered; frame buffer and processor instruction memory
Instruction cache 64K static RAM
Expansion Two SIMM sockets for DRAM (Apple kit adds 2 MB; up to 8 MB with third-party SIMMs)
Pixel depths 1, 2, 4, 8 or 24 bits per pixel
Maximum resolution 1152 × 870
NuBus Master and slave block transfers
Vertical refresh 66.7 or 75 Hz
Dot clock 12.2727, 30.24, 57.2832 or 100 MHz
Power consumption 20 W maximum
System software System 6.0.5 or later; 32-bit QuickDraw on the Macintosh II, IIx and IIcx; 2 MB of RAM minimum

Figures from Apple's specification sheet.[1][6]

How the acceleration works

[edit | edit source]

The card's main parts are a frame buffer controller that also acts as the Am29000's memory management unit, the Am29000, 64K of SRAM caching its instructions, a configuration ROM holding the declaration data and driver, a NuBus controller that handles block transfers as master and slave, DRAM for the GC software, the AC842 video chip with three DACs and colour tables, 2 MB of VRAM and a programmable pixel clock.[2]

The software is one file, "8•24 GC", placed in the System Folder. At start-up it loads GC QuickDraw and a small kernel onto the card and installs an interprocess link that catches QuickDraw drawing calls on the Macintosh and queues them for the card, so the application carries on while the card draws. A rocket icon at start-up shows that the software has loaded, and the control panel turns acceleration on and off. Programs that bypass QuickDraw, or replace its bottleneck routines, get no acceleration.[2][3]

Only one 8•24 GC in a machine accelerates; Apple's software uses the card in the lowest-numbered slot, and any others behave as plain 8•24 cards. The accelerating card also speeds up drawing on other display cards, most on the 4•8 and 8•24 because they accept NuBus block transfers.[2][7] Apple's sources disagree on what the card does with no monitor attached. A Tech Info Library article reviewed in May 1990 says it turns itself off and stops accelerating other displays unless pin 4 of the video connector is grounded; the develop article says it stays active so that it can still accelerate other monitors. If a GC with no monitor gives no acceleration, ground pin 4.[8][2]

Revisions

[edit | edit source]
8•24 GC revisions
Revision Service part ROM part RAM DAC part Notes
A 661-0606 341-0812 357S0010 ROM upgrade 076-1019 adds 16-inch display timing only
B 661-1642 341-0266 343S1075 New ROM and CLUT; 32,768 colours on the 16-inch display

Part numbers are from Apple's module identification manual and Tech Info Library.[9][10] The Rev. B card's new CLUT/DAC supports a 16-bit colour table. A Rev. A card with the upgrade ROM drives the Macintosh 16-inch Color Display but cannot show 16-bit colour, because there is no upgrade for the CLUT. The Rev. B software release made the card fully System 7 compatible and added gamma selection for the 16-inch and 21-inch displays.[11][12]

Displays

[edit | edit source]

Apple's specification sheet gives 256 greys on the High-Resolution Monochrome, Portrait and Two-Page displays, 16.7 million colours on the AppleColor High-Resolution RGB, and up to 16.7 million colours on interlaced devices, with convolution up to 256.[1] The 1996 service guide adds 16.7 million colours on the 12-inch RGB, Color Plus 14", Performa and multiple scan displays at 640 × 480; 32,768 colours at 832 × 624 on a Rev. B card (multiple scan displays need an adapter); 256 colours at 1152 × 870; and no support for the Basic Color Monitor, for 1024 × 768 or for 1280 × 1024.[13] Among third-party monitors Apple knew only of SuperMac's Color Two-Page and Platinum Two-Page displays, at up to 8 bits per pixel; RasterOps and SuperMac 19-inch monitors did not meet its timings.[14][15]

DRAM expansion

[edit | edit source]

The Macintosh Display Card DRAM Expansion Kit fits two DRAM SIMMs in the sockets on the card. Apple's service part is 661-0610, a 1 MB 100 ns SIMM. The extra memory holds large off-screen bitmaps.[6][13] Low End Mac reports that the sockets take paired 64-pin SIMMs of the Macintosh IIfx type at 80 ns or faster, up to two 4 MB SIMMs.[16] Remove the SIMMs before returning a card to Apple for exchange.[9]

Compatibility

[edit | edit source]
  • Apple lists the card as not compatible with the Macintosh IIsi, Quadra 700 and Quadra 900.[13]
  • Acceleration needs a 68020 or 68030 machine. On a 68040 Macintosh the card works only as an unaccelerated display card; in Apple's AV-series list the Rev. A card is incompatible with the Quadra 840AV and the Rev. B card works there unaccelerated.[16][17]
  • At its launch the card did not work with A/UX.[7]
  • The card draws up to 20 W. Add up the power of every card in a full machine: Apple gives 90 W for NuBus in six-slot Macintosh II models and 45 W in three-slot models.[7]

Troubleshooting

[edit | edit source]
8•24 GC software faults
Symptom Cause Action
Bus error at start-up after moving to System 7.5 Acceleration software incompatible with System 7.5 when 32-bit addressing is on Turn off 32-bit addressing, or remove the 8•24 GC control panel and run without acceleration[18]
Control panel icon crossed out at start-up File renamed Name the control panel exactly "8•24 GC"[19]
No acceleration on a Quadra or other 68040 machine Not supported on the 68040 Use the card unaccelerated[16]
No acceleration on a second GC card Only the lowest-slot GC accelerates Normal[2]

In Low End Mac's tests of a Rev. A card, a IIci running System 7.5.5 would not boot with the control panel installed, and a Quadra 650 did the same when set to 24-bit addressing.[16]

For hardware faults Apple's checklist for its video cards applies, in order:[6][13]

  1. Reseat the card.
  2. Reseat the DRAM SIMMs, if fitted.
  3. Check the video cable connections.
  4. Run the video tests. Apple specified MacTest IIfx for the 8•24 GC.
  5. Replace the DRAM SIMMs with known-good ones.
  6. Replace the card.
[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 Apple Computer, "Display Card 8•24 GC: Specifications (Discontinued)", Tech Info Library article 5423, last reviewed 21 March 1990, revised 14 September 1993, file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: system requirements; Am29000 at 30 MHz; 2 MB of VRAM as frame buffer and instruction memory; the DRAM Expansion Kit adding 2 MB and third-party SIMMs up to 8 MB; 64K SRAM instruction cache; display modes; master and slave block transfer; refresh and dot clock figures; 20 W power consumption; supported displays.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Guillermo Ortiz, "Macintosh Display Card 8•24 GC: The Naked Truth", develop (Apple Computer), issue 3 (1990), reproduced by MacTech at http://www.mactech.com/articles/develop/issue_03/824GC_V007.html (retrieved 2026-10-04). Source for: 5 to 30 times faster QuickDraw; display circuitry closely matching the 8•24; the components (MFB frame buffer controller, Am29000 at 30 MHz, 64K SRAM, configuration ROM, RDNC NuBus controller, up to 8 MB DRAM, AC842 chip, 2 MB VRAM, programmable pixel clock); sense-line monitor detection at start-up on the 8•24 and 8•24 GC; the GC staying active with no monitor connected; 8 bits on all monitors and 24 bits on the 13-inch; NuBus master block transfers and pseudo block transfers; only the lowest-slot GC accelerating; RS-170A and PAL output with convolution; the single "8•24 GC" file and its control panel; applications that bypass QuickDraw getting no acceleration.
  3. ↑ 3.0 3.1 Apple Computer, "Macintosh Display Cards Overview (2 of 3)", Tech Info Library article 5205 (TA40917), revised 16 July 1990, file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: convolution (1:2:1 weighting) on the 8•24 up to 8 bits per pixel and none on the 4•8; overscan mode of 512 × 384; the frame buffer controller gate array and its address translation, fitting 24-bit 640 × 480 into just over 900K of VRAM; the 8•24 GC keeping the alpha byte; the GC's Am29000, IPC and 5 to 30 times acceleration.
  4. ↑ Apple Computer, "Macintosh Display Cards Overview (1 of 3)", Tech Info Library article 5210 (TA40921), revised 16 July 1990, last reviewed 19 March 1990. In the archive.org collection Apple's Technical Information Library Articles, file TIL00001_to_TIL09432.pdf. Source for: the 4•8 supporting 256 colours or greys on the High-Resolution Monochrome and AppleColor High-Resolution RGB monitors and 16 greys on the Portrait and Two-Page displays; the 8•24 and 8•24 GC supporting 256 true greys on all Apple displays and 24-bit colour on the AppleColor High-Resolution RGB; RS-170 timing on all three cards; Apple Convolution on the 8•24 and 8•24 GC; programmable pixel clock and 100 MHz oscillator; 512K of VRAM on the 4•8 and 1 MB on the 8•24.
  5. ↑ Apple Computer, "Display Card 8/24: RasterOps 19" 724 Is Not Supported", Tech Info Library article 5969 (TA44108), last reviewed 27 July 1990, file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: the 8•24 and 8•24 GC having the same connector and pinouts and producing the same signals; the RasterOps 724 19-inch monitor supported by neither.
  6. ↑ 6.0 6.1 6.2 Apple Computer, Apple Service Technical Procedures: Macintosh Family, Volume Four (March 1991), "Macintosh Family Cards" section 2, "Macintosh II Video Cards": product descriptions p. 2.4 (rev. Nov 1990); Macintosh Display Card 4/8 upgrade pp. 2.10-2.11 (Jun 1990); troubleshooting video/display cards p. 2.12; illustrated parts list pp. IPL.13-IPL.15. Archive.org item Apple_Service_Technical_Procedures_Macintosh_Family_Volume_Four_1991-03_Apple_PN_072-0228 (retrieved 2026-10-04).
  7. ↑ 7.0 7.1 7.2 Apple Computer, "Macintosh Display Cards Overview (3 of 3)", Tech Info Library article 5818 (TA43882), revised 16 July 1990, file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: NuBus block transfer (master and slave on the 8•24 GC, slave only on the 4•8 and 8•24); the 8•24 GC accelerating other frame buffers, best on the 4•8 and 8•24; one GC accelerator per system; the VRAM Kit and DRAM Expansion Kit; System 6.0.5 and 32-bit QuickDraw requirements; the DB-15 to DB-25 adaptor for existing Portrait and Two-Page displays; A/UX; 20 W maximum for the GC and NuBus power budgets of 90 W (six-slot) and 45 W (three-slot); original Macintosh II ROMs; DB-15 pinout and DB-15 to DB-25 adaptor wiring.
  8. ↑ Apple Computer, "Macintosh Display Card 8/24GC and Raster Ops Monitors", Tech Info Library article 5477 (TA41836), last reviewed 3 May 1990, file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: supported sense codes and timings; with no monitor connected the card turning itself off and not accelerating other displays, unless pin 4 is grounded.
  9. ↑ 9.0 9.1 Apple Computer, Module Identification, Apple Service part number 072-8124, June 1994, hosted as File:Apple Service Module Identification Manual (June 1994).pdf, "Interface Cards" section: Display Card 8•24 pp. 4.1.8-4.1.9 (PDF pages 232-233), Display Card 4•8 pp. 4.1.10-4.1.11 (PDF pages 234-235), Display Card 8•24 GC p. 4.1.12 (PDF page 236).
  10. ↑ Apple Computer, "Display Card 8•24 & 8•24 GC: Identifying Rev & Upgrade ROM 1/96", Tech Info Library article 9913, created 29 January 1992, revised 31 January 1996, file TIL09433_to_TIL17062.pdf in the APPLE_TIL_ARTICLES collection. Source for: Rev. A and Rev. B service part numbers and ROM part numbers for the 8•24 and 8•24 GC; ROM upgrade part numbers 076-0548 and 076-1019; Rev. B ROMs giving page-white correction for the 21-inch and support for the 16-inch Color Display.
  11. ↑ Apple Computer, "Macintosh Display Cards 8•24 & 8•24 GC: Rev A/B Differences", Tech Info Library article 9858, created 18 February 1992, file TIL09433_to_TIL17062.pdf in the APPLE_TIL_ARTICLES collection. Source for: the Rev. B 8•24 GC's new CLUT/DAC supporting 16-bit colour; no 16-bit colour on an upgraded Rev. A GC or on the 8•24; older 8•24 and GC cards needing the ROM upgrade for the 16-inch Color Monitor.
  12. ↑ Apple Computer, "Macintosh Display Card 8•24 GC: Upgrade", Tech Info Library article 10053, created 11 March 1992, file TIL09433_to_TIL17062.pdf in the APPLE_TIL_ARTICLES collection. Source for: Rev. B hardware (new ROM and CLUT) with 16-inch display timing and 32,000-colour support; new software making the card fully System 7 compatible with gamma selection for the 16-inch and 21-inch displays; Rev. A owners needing the ROM upgrade for the 16-inch display; no upgrade path for the CLUT.
  13. ↑ 13.0 13.1 13.2 13.3 Apple Computer, Macintosh Displays and Video Cards service guide, September 1996, hosted as File:Apple Macintosh Displays and Video Cards Service Guide (September 1996).pdf (described at Apple Macintosh Displays and Video Cards Service Guide (1996)). Line drawings of the 4/8, 8/24 and 8/24 GC p. 324; video card parts list and notes pp. 325-326; troubleshooting chart p. 327; 4•8 and 8•24 GC upgrade procedures p. 330; Table 16, "Video Cards–Card Compatibility and Video Output Chart", pp. 342-343.
  14. ↑ Apple Computer, "Display Card 8/24 GC: Compatible Third-Party Monitors", Tech Info Library article 5777 (TA43817), last reviewed 12 June 1990, file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: SuperMac's Color Two-Page and Platinum Two-Page displays (1152 × 870) working with the card at up to 8 bits per pixel.
  15. ↑ Apple Computer, "Display Card 8/24GC: Third-Party Monitor Support", Tech Info Library article 5634 (TA43177), last reviewed 29 May 1990, file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: the sense pin codes, resolutions, dot clocks and refresh rates the card supports; RasterOps and SuperMac 19-inch displays not meeting them.
  16. ↑ 16.0 16.1 16.2 16.3 Low End Mac, "Macintosh Display Card 8•24 GC", https://lowendmac.com/1990/macintosh-display-card-8-24gc/ (retrieved 2026-10-04). Source for: no acceleration on 68040 Macs; driver versions for System 6 and 7; the hands-on test of a Rev. A card, in which a IIci would not boot with the control panel installed under System 7.5.5 and a Quadra 650 did the same in 24-bit mode; the two SIMM slots taking paired 80 ns or faster 64-pin SIMMs of the Macintosh IIfx type, up to 8 MB.
  17. ↑ Apple Computer, "AV Series: Apple NuBus Video Card Compatibility", Tech Info Library article 14695 (TA31196), file TA30000-TA39999.pdf in the APPLE_TIL_ARTICLES collection. Source for: the 4•8 and 8•24 (Rev. A and B) compatible with the Quadra 840AV, with the Rev. B ROM recommended for the 16-inch and 21-inch color monitors; the 8•24 GC Rev. A incompatible and Rev. B compatible only unaccelerated; the 24AC compatible with the 660AV and 840AV.
  18. ↑ Apple Computer, "System 7.5: 8•24 GC Card Compatibility (12/95)", Tech Info Library article 16469 (TA32657), file TA30000-TA39999.pdf in the APPLE_TIL_ARTICLES collection. Source for: a bus error at start-up on a IIci with System 7.5; the acceleration software being incompatible with System 7.5 with 32-bit addressing on; the two workarounds (turn off 32-bit addressing, or remove the 8•24 GC control panel and lose acceleration).
  19. ↑ Apple Computer, "8•24 GC Software Must Have Correct Name To Load (6/95)", Tech Info Library article 17940 (TA33898), file TA30000-TA39999.pdf in the APPLE_TIL_ARTICLES collection. Source for: the start-up icon crossed out when the control panel is misnamed; the required name "8•24 GC".


Retrieved from "https://wiki.retrotechcollection.com/index.php?title=Apple_8•24_GC_Card&oldid=23578"