original_query: What were the unique features of the TI-990 minicomputers?
query: What were the unique features of the TI-990 minicomputers?
answer: Unique features of the TI-990 included the ability to easily support multiprogramming using software-switchable processor registers for rapid context switching, and a memory model where registers were stored in memory and accessed via a Workspace Pointer.  It also had extended operation capabilities through plug-in hardware and an orthogonal instruction set.