Tandem NonStop I

The Tandem NonStop I, originally marketed as the Tandem/16 or T/16, was a modular fault-tolerant computer designed for continuous transaction processing. Systems combined independent processor modules, private memory and duplicated communication paths so that work could continue when an individual component failed.

Processes communicated through messages and could be paired with a backup process on another processor. This hardware and software design made the machine especially suitable for banking, stock exchanges, telecommunications and other applications where interruption or lost transactions carried a high cost.

Notable Features

• Systems were assembled from two to sixteen independent processor modules connected by dual Dynabus paths.
• Each processor used a proprietary 16-bit stack architecture with virtual memory and message-oriented interprocessor communication.
• Mirrored storage, dual controllers and multiple I/O paths extended fault tolerance beyond the CPUs.

Historical Significance

• Introduced in 1976, it established the commercial NonStop architecture and Tandem’s reputation for high-availability transaction processing.
• Its process-pair and shared-nothing design allowed individual hardware failures to be isolated without stopping the complete system.

Collector’s Notes

• Complete systems occupied multiple cabinets and were normally customised for a customer, so configurations vary considerably.
• Original processor boards, Dynabus hardware, disk controllers, cabinets and documentation are more representative than a single isolated module.

Specifications

Technical Information
Name	Tandem NonStop I
Manufacturer	Tandem Computers
Launched	Thursday, January 1, 1976
Discontinued	1981
Country	United States
CPU	Tandem proprietary 16-bit stack processor
Units Sold
Power	Redundant, serviceable system power supplies; requirements depended on cabinet configuration
Fault Tolerance	Process pairs, fail-fast processor modules, dual buses, mirrored disks and online serviceability
Architecture	16-bit stack-oriented TNS instruction set; shared-nothing multiprocessor design
Networking	Expand networking joined geographically separated NonStop systems
Operating System	Guardian operating system
Expansion / I/O	Dual Dynabus processor interconnect with redundant I/O paths
Keyboard	External operator console terminal keyboard
Storage	Mirrored fixed disks, removable disks and magnetic tape through dual-ported controllers
Sound	No general-purpose sound hardware
Graphics	Terminal-oriented text output; no integrated graphics subsystem
Display	External operator console terminal; no integrated display
ROM	Boot, diagnostic and processor microcode storage; capacity varied by generation and configuration
RAM	Private protected memory per processor; capacity depended on system configuration
CPU Speed	100 ns processor cycle; approximately 0.7 MIPS per processor