SGI O2

The O2 was an entry-level Unix workstation introduced in 1996 by Silicon Graphics, Inc. (SGI) to replace their earlier Indy series. Like the Indy, the O2 used a single MIPS microprocessor and was intended to be used mainly for multimedia. Its larger counterpart was the SGI Octane. The O2 was SGI's last attempt at a low-end workstation.

Originally known as the "Moosehead" project, the O2 architecture featured a proprietary high-bandwidth Unified Memory Architecture (UMA) to connect system components. A PCI bus is bridged onto the UMA with one slot available. It had a designer case and an internal modular construction. Two SCSI drives could be mounted on special caddies (1 in the later R10000/R12000 models due to heat constraints) and an optional video capture / sound cassette mounted on the far left side.

The O2 comes in two distinct CPU flavours; the low-end MIPS 180 to 350 MHz R5000- or RM7000-based units and the higher-end 150 to 400 MHz R10000- or R12000-based units. The 200 MHz R5000 CPUs with 1 MB L2-cache are generally noticeably faster than the 180 MHz R5000s with only 512 KB cache. There is a hobbyist project that has successfully retrofitted a 600 MHz RM7xxx MIPS processor into the O2.

There are eight DIMM slots on the motherboard and memory on all O2s is expandable to 1 GB using proprietary 239-pin SDRAM DIMMs. The Memory & Rendering Engine (MRE) ASIC contains the memory controller. Memory is accessed via a 133 MHz 144-bit bus, of which 128 bits are for data and the remaining for error-correcting code (ECC). This bus is interfaced by a set of buffers to the 66 MHz 256-bit memory system.

...
Wikipedia