the VGC in swapping palettes into and out of the video memory so that each scan line can have its own palette of 16 colors allowing for up to 3,200 colors on the screen at once. 320×200 pixels with 15 colors per palette, plus a fill-mode color. In this mode, color 0 in the palette is replaced by the last non-zero color pixel displayed on the scan line (to the left), allowing fast solid-fill graphics (drawn with only the outlines). 640×200 pixels with 4 pure colors. 640×200 pixels with up to 16 palettes of 4 pure colors. In this mode, the VGC holds 16 separate palettes of 4 pure colors in its own memory. Each of the 200 scan lines can be assigned any one of these palettes allowing for up to 64 colors on the screen at once. 640x200 pixels with up to 200 palettes of 4 pure colors. In this mode, the CPU assists the VGC in swapping palettes into and out of the video memory so that each scan line can have its own palette of 4 colors allowing for up to 800 colors on the screen at once. 640×200 pixels with 16 dithered colors. In this mode, two palettes of four pure colors each are used in alternating columns. The hardware then dithers the colors of adjacent pixels to create 16 total colors on the screen. Each scan line on the screen can independently select either 320- or 640-line mode, fill mode (320-mode only), and any of the 16 palettes, allowing graphics modes to be mixed on the screen. This is most often seen in graphics programs where the menu bar is constantly in 640-pixel resolution and the working area's mode can be changed depending on the user's needs. Audio The Apple IIGS's sound is provided by an Ensoniq 5503 Digital Oscillator Chip (DOC) wavetable synthesis chip designed by Bob Yannes, creator of the SID synthesizer chip used in the Commodore 64. The ES5503 DOC is the same chip used in Ensoniq Mirage and Ensoniq ESQ-1 professional-grade synthesizers. The chip has 32 oscillators, which allows for a maximum of 32 voices (with limited capabilities when all used independently), though Apple's firmware pairs them for 16 voices, to produce fuller and more flexible sound, as do most of the standard tools of the operating system (the Apple MIDISynth toolset goes even a step further for richer sound,