The IBM 308X is a line of mainframe computers that implemented the IBM System/370 architecture and, starting in 1983, the System/370 Extended Architecture, which extended the original 24-bit addressing to 31-bits, thereby allowing programs to access much larger sets of data. S/370-XA was used in the new MVS/SP V2 operating system and the Start Interpretive Execution (SIE) instruction used by the new Virtual Machine/eXtended Architecture Migration Aid.

The first model in the family, the Model 3081 Processor Complex, was introduced November 12, 1980. It consisted of a 3081 Processor Unit with supporting units. Later models in the series were the 3083 and the 3084. The 3083 was announced March 31 and the 3084 on September 3, both in 1982.

All three 308X systems, which IBM had marketed as "System/370-Compatibles," were withdrawn August 4, 1987.

The initial 3081 offered, the 3081D, was a 5 MIPS machine. The next offering, the 3081K, was a 7 MIPS machine. Last came the 3081G, again a 5 MIPS machine.

The 3081D was announced Nov 12, 1980; the 3081K came nearly a year later; the 3081G was introduced September 3, 1982 as part of the initial 3084 announcement. The 3081G was replacing the 3081D models.

"The IBM 3081 Processor Complex offers flexible growth steps in the 308X family of processors, between the 3083 Model Groups C, E, B and J over 3081G and 3081K to the 3084."

The 3081 was "two processors in a single box ... it was not possible to partition it and run it as two independent machines."

The dyadic concept offers "under the cover" dual processors.