Longest period of continual operation for a computer
Voyager Computer Command System
43:70 year(s):day(s)
Not Applicable ()

The computer system that has been in continual operation for the longest period is the Computer Command System (CCS) onboard NASA's Voyager 2 spacecraft. This pair of interlinked computers have been in operation since the spacecraft's launch on 20 August 1977. As of 29 October 2020, the CCS has been running for 43 years 70 days.

The CCS consists of two complete computers, with two processor units (each made using discrete components rather than a single microprocessor), two output units, and two power supplies. The two computers are interlinked enabling three different modes of operation – individual (each computer working on separate tasks), parallel (both working on the same task together), and tandem (both working on the same task independently). Each has around 70 kB of memory.

The CCS is the probe's primary computer, but there are two other computers onboard, the Flight Data Subsystem (FDS), and the Attitude and Articulation Control System (AACS). These handle tasks relating to the scientific instruments and attitude control, respectively. These elements are typically powered down unless needed, whereas the CCS is always active.

The CCS originally ran software written in the Fortran programming language, but this has been continually upgraded since its launch (software updates can be transmitted and installed remotely). The current software is written in a mixture of C and Fortran. The age of the computer and its codebase has caused problems for NASA in recent years. In 2015 Larry Zottarelli, the last of the project's original programmers, retired, and it was difficult to find a replacement with such in-depth knowledge of what now seem like ancient hardware and design principles.