The Power Macintosh 5500 and 6500 series computers and the 20th Anniversary Macintosh include an ATI 3D RAGE II 64-bit graphics and multimedia accelerator via the built-in ATI264GT graphics controller on their logic boards. The ATI264GT graphics controller contains the logic for video display. This graphics controller provides the following specific functions:
- Display memory controller, built-in drawing coprocessor, video scaler, color space converter, clock generator, and true color palette video DAC (digital-to-analog converter).
- Video CLUT (color lookup table).
- Hardware graphics acceleration with a 16-bit Z-buffer.
- Accelerates QuickDraw 3D rendering up to 6 times that of software-only acceleration.
- True color palette DAC supporting pixel clock rates to 135 MHz for 1280 by 1024 resolution at 75 Hz.
- Graphics and video line buffer for superior video scaling and playback quality.
- Hardware cursor up to 64 x 64 x 2.
- DCC1 and DDC2B plug-and-play monitor support.
- Supports synchronous graphics RAM (SGRAM) at up to 67 MHz memory clock, providing a bandwidth up to 536 MB per second.
- Graphics control accessible through the QuickDraw, QuickDraw 3D, QuickDraw 3D RAVE, and QuickTime components APIs.
A separate data bus handles data transfers between the ATI264GT IC and the display memory. The display memory data bus is 64 bits wide, and all data transfers consist of 32 bits at a time. The ATI264GT IC breaks each 64-bit data transfer into several pixels of the appropriate size for the current display mode of 4, 8, 16, 24, or 32 bits per pixel. The ATI264GT IC uses several clocks. Its transactions are synchronized with the PCI bus. Data transfers from the frame-buffer RAM are clocked by the MEM_CLK signal, which runs at 67 MHz. Data transfers to the CLUT and the video output are clocked by the dot clock, which has a different rate for different display monitors. The 2D graphics accelerator is a fixed-function accelerator for rectangle fill, line draw, polygon fill, panning/scrolling, bit masking, monochrome expansion, and scissoring.
All of the acceleration features are controlled by application software through the use of system software extensions. The Macintosh system software (Mac OS) extensions for accessing the ATI264GT graphics controller are:
- ATI 3D Accelerator - Links Apple QuickDraw 3D to ATI 3D hardware accelerator.
- ATI Graphics Accelerator - Provides for acceleration of 2D graphics operations.
- ATI Graphics Driver - PowerPC native video driver for the ATI video hardware
- ATI MPEG Accelerator - Provides hardware color space conversion, chroma interpolation and alpha blending while scaling of YUV-9 data stream for MPEG Acceleration.
- ATI Video Memory Manager - Keeps track of bitmaps and textures in offscreen memory on ATI 3D hardware accelerator.
- ATI YUV Accelerator - Provides hardware decoding and scaling of YUV data stream for QuickTime Acceleration.
Much of the above information was taken from the "Software Components for the 2D and 3D Hardware Graphics Accelerator" chapter of the Power Macintosh 5500 and 6500 Developer Notes. For more information, see the Power Macintosh 5500 and 6500 series or the 20th Anniversary Macintosh Developer Notes.