The TI-990 was a series of 16-bit minicomputers sold by Texas Instruments (TI) in the 1970s and 1980s. The TI-990 was a replacement for TI’s earlier minicomputer systems, the TI-960 and the TI-980. It had several uniquely innovative features, and was easier to program than its predecessors.

TI-990 models

The TI-990 processors fell into several natural groups depending on the original design upon which they are based and which I/O bus they used.

All models supported the Communications Register Unit (CRU) which is a serial bit addressable I/O bus. Also, supported on higher end models was the TILINE I/O bus which is similar to DEC’s popular UNIBUS. The TILINE also supported a master/slave relationship that allowed multiple CPU boards in a common chassis with arbitration control.

TILINE/CRU models

The following models used the TILINE as their principal mass storage bus:

• TI-990/5 — TMS-9900 microprocessor with 64K bytes of memory
• TI-990/10 — TTL processor with memory mapping support to 2M bytes of memory
• TI-990/10A — TMS-99000 microprocessor with memory mapping support to 1M bytes of memory
• TI-990/12 — Schottky TTL processor with memory mapping to 2M bytes, workspace caching, hardware floating point, extended mode instructions and writeable control store

CRU only models

The following models used the CRU as their principal bus:

• TI-990/4 — TMS-9900 microprocessor with 56K bytes of memory
• TI-990/9 — The original TTL implementation

Credit: Wikipedia