COS (Cray Operating System) 1.17 on a 80Mb Storage Module Device (CDC 9762 SMD) from Cray XMP serial 302/25 22nd June 1989.  Wikipedia entry states that there are "no known saved copies".  However, if someone has an operating CDC Storage Module Drive 9762 capable of reading an 80MB disk pack ... then, we can recover the operating system source.