the 1979 Iranian Islamic Revolution and the systems were never delivered. Longevity and follow-on systems The 9020As and 9020Ds were in service in North America until 1989 when they were finally replaced by IBM 3083 BX1 mainframes as part of the FAA's HOST Computer System (HCS) upgrade. The 3083s in turn were replaced with IBM 9672 RA4 parallel processing servers during the FAA's Host and Oceanic Computer System Replacement (HOCSR) completed in 1999. One reason for the 1999 upgrade was concern, probably unfounded, that the IBM 3083's microcode would not operate properly in the year 2000. At least during the first phase of the upgrade, the 9672s were running the FAA's original assembly language code in System/360 emulation mode. Because of the failure of the FAA's Advanced Automation System (AAS) project, the 9020E Display Channel Complexes lasted well into the 1990s. NATS in the UK had a 9020D system in service running NAS from 1974 to 1989, at which time NAS was rehosted on to an IBM 4381 system. This system was known as the Host Computer System (HCS), and it retained the System/360 technology Peripheral Adapter Modules (PAMs) from the 9020D. The three PAMs (IBM 7289s) were switched off for the last time 27 November 1997 when their replacement (SPRINT) came into service. Sources pictures of 9020E being recycled Article about the PAM final switch-off References Air traffic control 9020