The first of the External Stowage Platforms, called ESP-1 was carried on STS-102 Space Shuttle mission on Mar 8, 2001. It was carried into orbit on the underside of an Integrated Cargo Carrier (ICC), and it is smaller and unique in shape over the other platforms.
It was installed on the port side trunnion of the Destiny Laboratory Module.
STS-102
The first ORU installed was the PFCS (Pump Flow Control System)
Download file here
STS-100
The second ORU installed on ESP-1 was the DCSU (Direct-Current Swithching Unit) which was carried by STS-100 on the sidewall of the payload bay trunk. STS-100 was launched on Apr 19, 2001.
ESP-1 has not changed since STS-100 and it still remains unchanged ever since.
ISS early configuration
More current ISS configurations showing ESP-1
Download file here
US EVA-45
The PFCS (Pump Flow Control Subassembly) was rotated 90 degrees on Oct 10, 2017 for a future ammonia vent.
Current ESP-1 configuration as of Oct 10, 2017
AXM Paper Space Scale Models Blog 