RetroTechCollection

Apple Display Card 8•24

The Apple Macintosh Display Card 8•24 is a NuBus display card for the Macintosh II family with 1 MB of video RAM soldered to the board. It drives the AppleColor High-Resolution RGB Monitor at 24 bits per pixel (16.7 million colours) and gives 256 true grey levels on Apple's monochrome, Portrait and Two-Page displays.[1][2] Apple introduced it in March 1990 alongside the 8-bit Display Card 4•8 and the accelerated Display Card 8•24 GC.[3][2] The 4•8 is upgraded to the same specification with two VRAM SIMMs, and the 8•24 GC has the 8•24's display circuitry with a graphics coprocessor added.[4][5]

Apple Macintosh Display Card 8•24
The Rev. B card (661-0678) in Apple's 1994 module identification manual
Manufacturer Apple Computer
Type 24-bit NuBus display card
Release date March 1990
Interface NuBus, DB-15 video connector
Compatible Macintosh II family and Quadra computers with a NuBus slot
Power 7 W
Part number 661-0608 (Rev. A), 661-0678 (Rev. B)

Specifications

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Macintosh Display Card 8•24
Item Specification
Interface NuBus, slave block transfers supported
Video RAM 1 MB, soldered
Connector 15-pin D-style
Pixel depths 1, 2, 4, 8 or 24 bits per pixel
Maximum resolution 1152 × 870
Video output RS-343 analogue RGB; RS-170 interlaced timing with overscan and underscan
Sync Separate or composite, negative-going TTL
Vertical refresh 66.7 or 75 Hz, depending on display
Dot clock 12.2727, 30.24, 57.2832 or 100 MHz
Power consumption 7 W
System software System 6.0.5 or later; 32-bit QuickDraw on the Macintosh II, IIx and IIcx

Specifications from Apple's data sheet for the 4•8 and 8•24.[6][1]

Hardware

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A custom gate array is the frame buffer controller on the 4•8 and 8•24. It translates addresses so that 24-bit 640 × 480 fits into just over 900K of VRAM, ignoring the unused eighth byte of each pixel, which is why 1 MB is enough for 24-bit colour on a 13-inch display.[5] A programmable pixel clock chip and a 100 MHz oscillator let one card drive every Apple monitor of the time; the 100 MHz clock is for the Two-Page display.[2] The CLUT/DAC chip has three 8-bit DACs. In 24-bit mode it passes colour straight through; at lower depths it gives a palette of 256 colours out of 16.7 million.[6][2]

The card supports NuBus block transfers as a slave only. An 8•24 GC in the same machine uses this to accelerate drawing on an 8•24 more than on most other display cards.[4]

The 8•24 and 8•24 GC have the same connector and pinout and produce the same signals.[7]

Display modes

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8•24 display modes (Apple data sheet)
Display Resolution Colours or greys
Apple High-Resolution Monochrome Monitor 640 × 480 2, 4, 16 or 256 greys
AppleColor High-Resolution RGB Monitor 640 × 480 2, 4, 16, 256 or 16.7 million colours
Apple Portrait Display 640 × 870 2, 4, 16 or 256 greys
Apple Two-Page Monochrome Monitor 1152 × 870 2, 4, 16 or 256 greys
Interlaced video devices 640 × 480 2, 4, 16, 256 or 16.7 million colours (convolution up to 256)
Apple Color Display (14") 640 × 480 2, 4, 16 or 256 colours
Macintosh 16-inch Color Display 832 × 624 2, 4, 16 or 256 colours
Macintosh 21-inch Color Display 1152 × 870 2, 4, 16 or 256 colours

The 16-inch and 21-inch rows were added to the data sheet in June 1993.[6] The 16-inch display needs a Rev. B card or the ROM upgrade.[8] Apple's 1996 service guide adds the later displays: 16.7 million colours on the Macintosh 12" RGB, Color Plus 14", Performa displays and multiple scan displays at 640 × 480; 256 colours on the 16-inch and 21-inch displays, and on multiple scan displays at 832 × 624 and 1152 × 870 through a display adapter, with 832 × 624 needing a Rev. B card; nothing at 1024 × 768 or 1280 × 1024; and no support for the Apple Basic Color Monitor.[9] The card cannot switch resolution on a multiple scan display without an adapter, and it has no 16-bit mode.[3][10]

Revisions and ROM upgrade

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8•24 revisions
Revision Service part ROM part Notes
A 661-0608 – Exchanged for 661-0678
B 661-0678 341-0868 Page-white correction for the 21-inch display; supports the 16-inch display

A Rev. A card is upgraded to Rev. B with ROM kit 076-0548, the same kit as for the 4•8.[11][12][9] Apple described the upgrade as mainly for PAL timing. The original card already drives the 21-inch Color Display; the new ROM adds the 16-inch display, announced in January 1992, and a choice of 9300 K or 6500 K white point.[8] Read the part number on the ROM to tell the revisions apart.[12][11]

Interlaced video and NTSC

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The card produces RS-170-A interlaced video. It uses Apple Convolution, which averages each line with the lines above and below in a 1:2:1 ratio to stop thin horizontal lines flickering; convolution works up to 8 bits per pixel and switches off in 24-bit mode.[5][13] For an overscanning monitor, such as a television, the card can be switched to an overscan mode of 512 × 384 so that the whole image stays visible.[5] No software switch is involved: a correctly wired cable puts the card into its interlaced mode. The interlaced signal is black and white unless an RGB-to-NTSC converter such as the RasterOps Video Expander or Truevision VIDI/O Box is used, and the card does not accept external sync.[14][13]

Monitors and connector

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The card reads monitor sense pins 4, 7 and 10 (SENSE0 to SENSE2) at start-up and configures itself for the display it finds.[15] A third-party monitor works only if it matches the timing of one of the Apple displays and is wired with that display's sense code.[16][7]

Sense codes (10, 7, 4; 0 = grounded, 1 = open)
Code Display Resolution Dot clock (MHz) Vertical (Hz) Horizontal (kHz)
0 0 1 Portrait Display 640 × 870 57.2832 75 68.9
0 1 1 Two-Page Monochrome 1152 × 870 100 75 68.7
1 1 0 12-inch Monochrome or 13-inch AppleColor RGB 640 × 480 30.24 66.7 35.0
DB-15 video connector (4•8, 8•24 and 8•24 GC)
Pin Signal Pin Signal
1 Red video ground 9 Blue video
2 Red video 10 Monitor ID bit 3 (SENSE2)
3 Composite sync 11 Composite and vertical sync ground
4 Monitor ID bit 1 (SENSE0) 12 Vertical sync
5 Green video 13 Blue video ground
6 Green video ground 14 Horizontal sync ground
7 Monitor ID bit 2 (SENSE1) 15 Horizontal sync
8 No connection Shell Chassis ground

Owners of Portrait and Two-Page displays bought before these cards need a DB-15 to DB-25 adaptor.[4]

Compatibility

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  • Any Macintosh II family computer with a free NuBus slot takes the card. The Macintosh II, IIx and IIcx need the 32-bit QuickDraw file for 24-bit colour; the IIci and IIfx have 32-bit QuickDraw in ROM. Apple recommends at least 2 MB of RAM for 24-bit work.[4][6]
  • A Macintosh II with its original ROMs does not run the display cards properly. Apple ran a service programme to replace those ROMs.[4]
  • Apple's 1996 service guide lists the card for all Macintosh II and Quadra computers.[9] It works in the Quadra 840AV; Apple recommends the Rev. B ROM there for the 16-inch and 21-inch displays.[17] Low End Mac reports that it does not suit the Centris and Quadra 660AV.[3]
  • Apple does not support the RasterOps 724 19-inch monitor on this card.[7]

Troubleshooting

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Apple serviced the card by module exchange.[12] Its checklist for Macintosh II video cards also has steps for reseating and replacing socketed memory, which the 8•24 does not have; the rest, in order, is:[1][9]

  1. Reseat the card in its NuBus slot.
  2. Check the video cable at both ends.
  3. Run the video tests. Apple specified MacTest IIfx for the 4•8, 8•24 and 8•24 GC.
  4. Replace the card.

A card that shows nothing on a third-party monitor may be reading the wrong sense code; check the cable wiring against the table above before condemning the card.[16] A card that will not show 16-bit colour is working normally: the 8•24 has no 16-bit mode.[10]

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References

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  1. ↑ 1.0 1.1 1.2 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).
  2. ↑ 2.0 2.1 2.2 2.3 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.
  3. ↑ 3.0 3.1 3.2 Low End Mac, "Macintosh Display Card 8•24", https://lowendmac.com/1990/macintosh-display-card-8-24/ (retrieved 2026-10-04). Source for: introduction in March 1990; 12-inch card; incompatibility with the Centris and Quadra 660AV; no 16-bit colour; no resolution switching without an adapter on multiple scan displays; Rev. B adding 832 × 624.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 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.
  5. ↑ 5.0 5.1 5.2 5.3 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.
  6. ↑ 6.0 6.1 6.2 6.3 Apple Computer, "Display Card 4/8 and 8/24 Specifications (Discontinued)", Tech Info Library article 5422, revised 20 June 1994 (change history 28 June 1993), file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: system requirements; NuBus slave block transfer; 15-pin connector; 1, 2, 4, 8 or 24 bits per pixel; resolution up to 1152 × 870; convolution on the 8•24 up to 8 bits; RS-343 video with RS-170 interlaced timing; sync; 66.7 or 75 Hz vertical refresh; dot clocks of 12.2727, 30.24, 57.2832 and 100 MHz; 7 W power consumption; display modes for each card.
  7. ↑ 7.0 7.1 7.2 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.
  8. ↑ 8.0 8.1 Apple Computer, "Macintosh Display Card 8•24: Benefits of ROM Upgrade", Tech Info Library article 8698, created 5 September 1991, last updated 5 February 1992, file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: the ROM upgrade being primarily for PAL timing; the original card driving the 21-inch Color Display; the upgrade needed for the 16-inch Color Display announced in January 1992; choice of 9300 K or 6500 K white point; service upgrade kit 076-0548.
  9. ↑ 9.0 9.1 9.2 9.3 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.
  10. ↑ 10.0 10.1 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.
  11. ↑ 11.0 11.1 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.
  12. ↑ 12.0 12.1 12.2 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).
  13. ↑ 13.0 13.1 Apple Computer, "Display Card 8/24: RS-170 External Sync", Tech Info Library article 5860 (TA44002), last reviewed 5 July 1990, file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: the 8•24 and 8•24 GC not accepting external sync; production cards meeting RS-170-A; interlaced output black and white without a converter.
  14. ↑ Apple Computer, "Macintosh Display Card 8/24: NTSC Video Encoding", Tech Info Library article 5859 (TA43998), file TIL00001_to_TIL09432.pdf in the APPLE_TIL_ARTICLES collection. Source for: no software switch to NTSC interlaced mode, a configured cable being all that is needed; colour NTSC needing an RGB-to-NTSC converter such as the RasterOps Video Expander or Truevision VIDI/O Box, which accept the cards' RS-170-A output; convolution only to 8 bits.
  15. ↑ 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.
  16. ↑ 16.0 16.1 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.
  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.


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