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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.