[1] It is also the first computer from Apple to be housed in an 18.6 inch (47 cm) tall mid-tower form factor, which by 1991 had gained momentum with PC manufacturers as a suitable design for departmental servers.

[1] The Quadra 900 could be upgraded to 256 megabytes of RAM,[2] an astronomical amount for the time, when a typical midrange system would come equipped with 2–4 MB.

The high RAM and storage capacity, along with the expandability of five NuBus 90 slots and fast 25 MHz processor, made it a very useful computer for scientific or design work.

Featuring 16 slots for 30-pin SIMMs (installed in groups of four),[2] Quadra 900s with full complements of RAM were exceedingly rare due to the high cost (many thousands of dollars) of the SIMMs at the time.

In Secure mode, the floppy drive and ADB port are disabled, offering a degree of local protection.