The MIPS R4400 is the most commonly found SGI system found on the 2nd-hand market these days (circa. 2001; machines are from the mid 1990s). The R4400 comes in PC and SC flavors. PC stands for Primary Cache and SC means Secondary Cache (i.e. it has both a PC and SC). It uses the MIPS III instruction set, unlike the current R1x000 class that uses the MIPS IV set, however it is, like all MIPS, backwards compatible. It also contains an onbaord MMU with a TLB (to provide rapid virtual to physical address translation) and contains an on-chip floating point unit. The R4400 processors contain 16 KB of instruction cache and 16 KB of data cache for a total of 32 KB of on-chip 1st level cache and have 32 64-bit integer registers and an equal amount of floating point registers. The R4400 processor can support up to 4 MB of off-chip secondary level 2 cache and all of the 1st level and 2nd level cache control logic resides on-chip.
Systems that use the R4400