Macintosh Quadra Built-In Video, Part 3: VRAM Configurations
This is the third in a series of articles which describes the capabilities of the built-in video of the Quadra 700 and 900.

The Quadra frame buffer supports a variety of pixel depths, from 1 to 32 bits per pixel (bpp). The supported pixel depths (1, 2, 4, 8, or 32 bpp) depend on the display resolution and the amount of VRAM in the Quadra. The fully expanded capability of both Quadras is the same, i.e., both the 900 and 700 can be expanded to 2 MB of VRAM. However, note that 512K of VRAM is the minimum configuration for the Quadra 700 whereas it is 1MB of VRAM for the Quadra 900 (this is the amount of VRAM soldered on the motherboard). The Quadra 700 has 6 VRAM expansion slots, while the 900 has only 4. Also note that only 0.5 MB, 1 MB, and 2 MB configurations are supported (i.e., 1.5 MB is not supported).

The Quadra 700 and 900 can be expanded using 256K (i.e., 128K x 16) 100 nS VRAM SIMMs. These are the same as the VRAM SIMM shipped in the base configuration of the Macintosh LC, or the VRAM SIMMs used to expand an Apple 4*8 video card to an 8*24 card. Note that the 512K VRAM SIMMs used to upgrade the Mac LC will _not_ work in a Quadra. (The 256K SIMMs removed from an LC when performing a VRAM upgrade will work, however. All those old 256K VRAM SIMMs laying around from upgraded LCs can be used to upgrade Quadra 700s and 900s!) The DRAM SIMMs used to upgrade an 8*24GC video card will also not work.

The following chart lists the Quadra 700 & 900 built-in video's maximum pixel depth supported depending upon the VRAM configuration:

Display size 512K VRAM 1MB VRAM 2MB VRAM

--------- -------- --------

12-inch landscape

384 x 512

(such as 12" RGB) 8 bpp 32 bpp 32 bpp

12-inch Monochrome

640 x 480 8 bpp 8 bpp 8 bpp

13-inch RGB & VGA

640 x 480 8 bpp 8 bpp 32 bpp

SVGA

800 x 600 8 bpp 8 bpp 32 bpp

15-inch Portrait (b/w)

640 x 870 4 bpp 8 bpp 8 bpp

16" Color,

832 x 624 8 bpp 8 bpp 32 bpp

2-Page Display (b/w)

1152 x 870 4 bpp 8 bpp 8 bpp

21" Color

1152 x 870 4 bpp 8 bpp 8 bpp

PAL without convolution

underscan-640x480 8 bpp 8 bpp 32 bpp*

overscan-768x576 8 bpp 8 bpp 32 bpp*

PAL with convolution

underscan-640x480 n.a. 8 bpp 8 bpp

overscan-768x576 n.a. 8 bpp 8 bpp

NTSC without convolution

underscan-512x384 8 bpp 8 bpp 32 bpp

overscan- 640x480 8 bpp 8 bpp 32 bpp

NTSC with convolution

underscan-512x384 n.a 8 bpp 8 bpp

overscan- 640x480 n.s 8 bpp 8 bpp

*Note there are two ways to cable a PAL monitor to a Quadra; only by using the proper extended sense code are you able to achieve 32 bits per pixel. For details, refer to the previous article on Quadra video sense pinouts.

- Dale Adams

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