Unicos and other operating systems

Unicos is the operating system(s) that enabled application software and users to exploit Cray hardware.  Unicos provided a Unix based envrionment with many extensions needed for systems with multiple users and a complex workloads. Unicos provided added security, resource control, programming languages, data management features as well as processing accounting.

Unicos versions (from Wikipedia)

Cray have released several different OSs under the name UNICOS, including:

  1. UNICOS: the original Cray Unix, based on System V. Used on the Cray-1Cray-2X-MPY-MPC90, etc.
  2. UNICOS MAX: a Mach-based microkernel used on the T3D‘s processing elements, in conjunction with UNICOS on the host Y-MP or C90 system.
  3. UNICOS/mk: a “serverized” version of UNICOS using the Chorus microkernel to make a distributed operating system. Used on the T3E. This was the last Cray OS really based on UNICOS sources, as the following products were based on different sources and simply used the “UNICOS” name.
  4. UNICOS/mp: not derived from UNICOS, but based on IRIX 6.5. Used on the X1.
  5. UNICOS/lc: not derived from UNICOS, but based on SUSE Linux. Used on the XT3XT4 and XT5. UNICOS/lc 1.x comprises a combination of
    1. the compute elements run the Catamount microkernel (which itself is based on Cougaar)
    2. the service elements run SUSE Linux
  6. Cray Linux Environment (CLE): from release 2.1 onwards, UNICOS/lc is now called Cray Linux Environment
    1. the compute elements run Compute Node Linux (CNL) (which is a customized Linux kernel[1])
    2. the service elements run SUSE Linux Enterprise Server

See also Cray Operating systems in the FAQ

Unicos Flyers


UnicosAsAGuest – Document by Dennis M. Ritchie describing a Operating System Guest feature for Unicos.

Early Evaluation for the Cray X-1 pap183-3 – Document by Dennis M. Ritchie describing an Early implementation of Unicos on AT&T Cray XMP.

  Cover of the original Unicos release notice.

Flyer for UnicosMax the version used on the T3E and later systems.

Other operating systems

In the early days Cray provided a rudimentary batch operating system called COS. A large government lab, desiring more direct interactivity, developed a time sharing system called CTSS. Unicos was introduced with the Cray-2 but, after a migration program, ran on most systems XMP onwards.

COS is described in these training documents. Cray-1 SWFE 2 COS Operations  and   Cray-1 SWFE 1 COS User

Another more specialist customer used “Folklore” for direct interactions. This extracted, redacted, now unclassified document, ( also published here) explains the benefits and history of the Folklore operating system.


Our correspondant Jim notes ….

I spent much of my early years working for Cray as a site engineer at an “SS” site. Sites that didn’t want their identity made public would be
given an SS designation along with a number, i.e. “SS 123”. Even though the acronym stood for “Special Systems” within
Cray we referred to them as “Secret Sites”. I was surprised to find when I started work at the SS site that they were not running
COS, but an entirely different operating system that had been developed in house. All information about the operating system “Folklore”was classified,
we could not talk about it outside of the site.

Recently I found that the National Security Agency (NSA) had declassified and released information about Folklore, the 
operating system that they developed and were running on the system I was maintaining. Attached is a copy of “Cryptolog”, a
declassified internal NSA publication that I found on the web that contains on page 11 an article about Folklore and how it was used.
There is even a picture of an X-MP at the end of the article.
One interesting fact that I do know about the Folklore operating systems is why it was called “Folklore”. The dictionary definition of
Folklore is “The traditional beliefs, customs, and stories of a community, passed through the generations by word of mouth.”
The story goes that as this was an internal product that was constantly being revised and having functionality and updates added, it
was difficult to keep user documentation up to date. Often new hires would ask where they could find a training manual or a user
guide and the common response was “there isn’t one, it’s folklore!” … hence the name stuck !
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