Many people, even those who have left in just the last couple of years, are quite confused as to what any of the entities are/were anymore. In fact it would take at least a 20-slide interactive powerpoint presentation to explain all the plate tectonics and no one has patience for THAT!! The Perkin-Elmer Corporation (PKN), now gone, subsequently became PE Corporation and then Applera Corporation.
       PE Corporation, in the late 1990's was composed of Applied Biosystems (ABI), Celera Genomics (CRA) and the Analytical Instrument Group.  EG&G purchased the Analytical Instrument Group from PE Corporation in 1999. EG&G then scrapped their original name and took the hyphen out of Perkin-Elmer to become PerkinElmer, Inc. (PKI).  Their operations have recently been retitled: "PerkinElmer Life and Analytical Sciences" since their biotools and analytical instuments businesses were combined. Headquarters for PerkinElmer,Inc. is Wellesley, MA and the Analytical Instruments are now located in Shelton, CT.
      Applera Corporation headquarters are in Norwalk, CT.  Applied Biosystems(ABI) operations are in Foster City, CA. Celera Genomics (CRA) is located in Rockville. MD. Celera Diagnostics (a diagnostic company) is a joint venture between Applied Biosystems and Celera Genomics.
     I've included the websites in current vogue in case people are trying to find the current incarnation of their favorite technology or product line and which entity has carried it forth.

For Applera: http://www.applera.com  and   www.appliedbiosystems.com

For PerkinElmer:   www.perkinelmer.com