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The SGI Visual Workstations (models 320 and 540) are based around
the Cobalt, Lithium, and Arsenic ASICs. The Cobalt ASIC is the
main system ASIC which interfaces the 1-4 IA32 cpus, the memory
system, and the I/O system in the Lithium ASIC. The Cobalt ASIC
also contains the 3D gfx rendering engine which renders to main
system memory -- part of which is used as the frame buffer which
is DMA'ed to a video connector using the Arsenic ASIC. A PIIX4
chip and NS87307 are used to provide legacy device support (IDE,
serial, floppy, and parallel).
The Visual Workstation chipset largely conforms to the PC architecture
with some notable exceptions such as interrupt handling.