Although it uses 32-bit instructions, the SE/30 ROM, like the IIx ROM, includes some code using 24-bit addressing, rendering the ROM "32-bit dirty".
This limited the actual amount of RAM that can be accessed to 8 MB under System 6.0.8.
A system extension called MODE32 enables access to installed extra memory under System 6.0.8.
Under System 7.0 up to System 7.5.5 the SE/30 can use up to 128 MB of RAM.
 Alternatively, replacing the ROM SIMM with one from a Mac IIsi or Mac IIfx makes the SE/30 "32-bit-clean" and thereby enables use of up to 128 MB RAM and System 7.5 through OS 7.6.1.

A standard SE/30 can run up to System 7.5.5, since Mac OS 7.6 requires a 32-bit-clean ROM.

Additionally, the SE/30 can run A/UX, Apple's older version of a Unix that was able to run Macintosh programs.

Though there was no official upgrade path for the SE/30, several third-party processor upgrades were available.
A 68040 upgrade made it possible to run Mac OS 8.1, which extended the SE/30's productive life for many more years.
The Micron Technology Xceed Gray-Scale 30 video card fit into the SE/30's Processor Direct Slot, enabling it to display greyscale video on its internal display, the only non-color compact Mac able to do so.
Although it uses 32-bit instructions, the SE/30 ROM, like the IIx ROM, includes some code using 24-bit addressing, rendering the ROM "32-bit dirty". This limited the actual amount of RAM that can be accessed to 8 MB under System 6.0.8. A system extension called MODE32 enables access to installed extra memory under System 6.0.8. Under System 7.0 up to System 7.5.5 the SE/30 can use up to 128 MB of RAM.  Alternatively, replacing the ROM SIMM with one from a Mac IIsi or Mac IIfx makes the SE/30 "32-bit-clean" and thereby enables use of up to 128 MB RAM and System 7.5 through OS 7.6.1.
A standard SE/30 can run up to System 7.5.5, since Mac OS 7.6 requires a 32-bit-clean ROM.
Additionally, the SE/30 can run A/UX, Apple's older version of a Unix that was able to run Macintosh programs.
Though there was no official upgrade path for the SE/30, several third-party processor upgrades were available. A 68040 upgrade made it possible to run Mac OS 8.1, which extended the SE/30's productive life for many more years. The Micron Technology Xceed Gray-Scale 30 video card fit into the SE/30's Processor Direct Slot, enabling it to display greyscale video on its internal display, the only non-color compact Mac able to do so.
Macintosh SE/30