Tandem NonStop CLX

The Tandem NonStop CLX brought the Guardian-compatible fault-tolerant architecture into a smaller and less expensive office-scale cabinet. Highly integrated CMOS gate arrays reduced the processor from several boards to one while duplicated CPU logic checked every operation.

The CLX targeted branch offices, remote transaction sites and smaller organisations that needed continuous availability. Later CLX 700 and CLX 800 revisions improved performance while retaining compatibility with larger Tandem networks.

Notable Features

• A one-board CMOS processor used duplicated lock-stepped CPU logic for error detection.
• The cabinet was designed for ordinary office environments rather than a traditional raised-floor computer room.
• CLX 600, 700 and 800 revisions progressively increased performance within the compact family.

Historical Significance

• CLX extended Tandem’s market from central data centres to distributed branch and edge installations.
• Its integrated processor foreshadowed the move away from large multi-board proprietary CPUs.

Collector’s Notes

• CLX model and processor revision should be recorded because 600, 700 and 800 versions differ significantly in performance.
• Paired processors and mirrored storage remain essential to understanding a complete working system.

Specifications

Technical Information
Name	Tandem NonStop CLX
Manufacturer	Tandem Computers
Launched	Thursday, January 1, 1987
Discontinued	Early 1990s
Country	United States
CPU	Tandem proprietary CLX processor
Units Sold
Power	Redundant, serviceable system power supplies; requirements depended on cabinet configuration
Fault Tolerance	Two lock-stepped CPU cores per processor board, paired processors, dual paths and mirrored disks
Architecture	Compact CMOS implementation of the TNS stack architecture
Networking	Expand networking with enterprise communications protocols
Operating System	Guardian 90 / Guardian 90XF
Expansion / I/O	Duplicated system interconnect with redundant I/O paths
Keyboard	External operator console terminal keyboard
Storage	Mirrored hard disks and tape options through dual 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	Protected private memory per processor; capacity varied by CLX revision
CPU Speed	CLX 600: 133 ns cycle and about 1 MIPS; CLX 700: 91 ns and about 1.5 MIPS; later CLX 800 faster