SGI Personal IRIS

 General Information


The Personal Iris are rather old SGI hardware. There are four base models, each with a different mainboard and CPU plus there are some different graphic options.


Model CPU Bus Memory
4D/20 R3000 at 12MHz 10MHz 8MB to 64MB SIMMS with parity
4D/25 R3000 at 20MHz 10MHz 8MB to 64MB SIMMS with parity
4D/30 R3000 at 30MHz 30MHz 8MB to 128MB propritary Memory
4D/35 R3000 at 35MHz 30MHz 8MB to 128MB propritary Memory

The mainboards of 4D/20 and 4D/25 are essentially the same, only the CPU speed is different. The same holds for the models 4D/30 and 4D/35.


For the 4D/20 and 4D/25 you can use normal 1MB and 2MB SIMMs with parity for upgrading memory. These modules are 30 Pin SIMM modules similar to those used in the PC industry. They came in capacities of 1 MB per module, or a “tall” module that could hold 2 MB. In the Personal IRIS these modules had to be installed in groups of 4 and there are totally 16 memory slots.

Theoretically also 4MB SIMMs are supported, but due a bug in the PROM only some types are detected correctly. But fortunately there is a workaround found on this site. Basically you have to boot and go into the PROM. Then try hinv and check the memory configuration detected. If it matches the physical RAM, then you are lucky and can continue. If the reported sie is incorrect, you should enter

fill -v 0 0xa0400000

In order to initialize the memory. Then reboot your machine (do NOT turn it off) and try hinv again. It should display the correct memory size now.

For the 4D/30 and 4D/35 you need different modules. These memory modules were custom designed by Silicon Graphics and were second sourced by some third party memory manufacturers. These modules were easy to recognize since there was a custom chip on the back side of the module. They were used in both the R3000 based Personal IRISs and the R3000 based Indigos. They were available in capacities of 2, 4 and 8 MBytes. They would typically have a sticker on the backside denoting the size of the module. In the Personal IRIS these modules had to be installed in groups of 4 and there are totally 16 memory slots.

Graphic Options

There are three different graphic options available for the Personal Iris. But note that the Elan option does only work in the 4D/30 and 4D/35, whereas the two other options work in all machines.

Graphic Cardset Features
Entry / G GR1, GR1.1, GR1.2 or GR1.5
BP4 (optionally)
ZB3 (optionally)
8bit colour, BP4 upgrades this to 24bit and ZB3 adds a 24bit Z-buffer
TG GR1.2 or GR1.5 8-bit graphics
24bit colour
24bit Z-buffer
Elan GR2 24bit colour
24bit Z-buffer

The Elan boardset is the fastest and uses a new architecture. Note that there are apparently two different flavours of GR1, as seen by the version numbers. GR1.0 and GR1.1 both use the RE1 raster engine whereas GR1.2 and GR1.5 use the better RE2 raster engine, which supports more features and seems to be faster. See this page at "This Old SGI" for further details.

Audio Options

The 4D/2x has a built audio I/O and there is a so called Magnum Audio Option for 4D/35.


As you can see at the model section, there is a difference between the older models (4D/20 and 4D/25) and the newer models (4D/30 and 4D/35) concerning memory. Whereas the old models can use standard 30pin SIM modules with parity, the newer models need proprietary RAM which is identical to the RAM modules used in a R3000 Indigo.

The Keyboard

The Personal Iris uses a custom keyboard - the computer has a DB9 female connector on its back. Fortunately you can use an Indigo keyboard using a simple adaptor.

The Power Supply

According to some people, the power supply of a Personal Iris is a somewhat weak point. Sometimes it is sufficient to replace one of the two fuses inside the power supply. If this doesn't help, there is a comparable simple hack to use a standard ATX power supply, as described here.

My System

I only own one Personal Iris 4D/25, and one Personal Iris 4D/35, and I guess that this is enough for me.