SGI Indy - Processors

Processors

Indy's motherboard has a socket for the Processor Module (PM). Early Indys used a 100 MHz MIPS R4000PC microprocessor, which quickly proved inadequate. The Indy, at the bottom of SGI's price list, was then upgraded with the MIPS R4400 and the low-cost, low-power-consumption Quantum Effect Devices (QED) R4600. The R4600 had impressive integer performance, but had poor floating-point capability. This, however, wasn't too large of a problem in a system that was generally not designed for floating-point-intensive applications. For this reason, the R4600 made an appearance outside the Indy line just once, and only briefly, in the SGI Indigo². This series of microprocessor issues, along with the relatively low-powered graphics boards, lower maximum RAM amount, and relative lack of internal expansion ability compared to the SGI Indigo led to the Indy being pejoratively described amongst industry insiders as "An Indigo without the 'go'."

As the R4600 chip itself has no L2 cache controller, an external controller was used to add 512K of L2 cache. R4600s processor modules, both with an L2 cache (SC) and without (PC), are common in the Indy. At the same clock rate, the SC version of the processor module is generally 20 to 40 percent faster than the PC version, due to the memory cache.

The Indy was also the first SGI machine to utilize the QED R5000 microprocessor, which offered significant advantages over the R4400 and R4600 it replaced.