Much less noise.  That was my initial thought when this box was first powered.  The 4500 sounds like a jet engine.  I was particularly excited about the Juniper EX4550 because it addressed a number of things that were less than ideal about the EX4500. Soem of the differences ciuyld be argued as either oa pro or con depending on deployment scanerio, but for what we’re looking for, the 4550 is far better. 4550 Single PFE, 4500 dual PFE Single PFE being more desirable for us since cross box traffic doesn’t potentially need to transit across another PFE introducing a tad more latency. ## Dual power supply in the 4550.  This one is a no brainer for us.  Redundancy is better. 32 line rate 1G/10G ports on the 4550.  40 on the 4500.  32 is plenty for us and is a worth while trade to get a single PFE. Ours came with JUNOS 12.2R1.8. root@EX-4550> show chassis hardware Hardware inventory: Item     Version     Part number Serial number Description Chassis LX0212450466 EX4550-32F Routing Engine 0 REV 12 750-045402 LX0212450466 EX4550-32F FPC 0 REV 12 750-045402 LX0212450466 EX4550-32F CPU BUILTIN BUILTIN FPC CPU PIC 0 BUILTIN BUILTIN 32x 1G/10G SFP/SFP+ Xcvr 31 NON-JNPR AN07452H1V SFP-T Power Supply 0 REV 03 740-044332 1G032240641 JPSU-650W-AC-AFI Power Supply 1 REV 03 740-044332 1G032240660 JPSU-650W-AC-AFI Fan Tray Fan Module, Airflow In (AFI)