While NCAR's Computing Facility (CF) staff closely monitored the progress of an early array processor, the ILLIAC IV, it became clear by 1970 that extending computing capability at NCAR beyond the Control Data Corporation (CDC) 6600 would be provided by either a CDC 7600 or an IBM System 360, Model 195. In benchmark tests run in early 1970, the CDC 7600 won by a slight margin. NCAR's CDC 7600, serial number 12, was delivered in May 1971, just before the NCAR Mesa Laboratory's computer facility complex was expanded in July.
The CDC 7600 had a small-core memory of 65,536 60-bit words and a a clock speed of 27 nanoseconds. It generally ran at five times the speed of the CDC 6600. This represented the last time that large a general increase of speed was available from a single processor.
The 7600 system included an NCAR-developed FORTRAN 70 compiler, and because the operating system had been developed by the NCAR CF, users had a uniform software environment on both the 6600 and 7600. Most users could run on either system without changes. This uniformity was difficult to accomplish because the machines' architectures differed substantially. Such a uniform operating environment would not return again until the late 1980s when UNICOS, a UNIX-based operating system, began to be used on the CRAY supercomputers at NCAR.
However, NCAR's CDC 7600 was not as stable as its CDC 6600. Its low mean-time-to-failure forced the CF to put extremely good job- and file-recovery procedures into the system. This took a few years to accomplish, by which time the aggravation level was high for users.
In 1980, during the CDC 7600's time at NCAR, the NCAR Computing Facility (CF), formerly a part of NCAR's Atmospheric Technology Division (ATD), was reorganized as the Scientific Computing Division (SCD) of NCAR.
NCAR's CDC 7600 was operated for nearly twelve years. NCAR augmented its computatonal capacity by acquiring the first production Cray-1A system, serial number 3. Those two systems served NCAR's computational needs until the 7600 was decommissioned and replaced in the spring of 1983 by a second Cray-1A, serial number 14.