Analysts said the large scale of the implementation validates claims that thin client systems - terminals that leave most computing functions to a central server - can substantially reduce the total cost of ownership of PCs.
Thin clients have long been touted as a low-cost alternative to traditional desktop PCs but there have been few implementations of this size. Tony Lock, senior analyst at Bloor Research, said, "It is a recognition that centralisation has its place."
American Express spokesman Tony Mitchell said the thin clients would replace existing desktop and laptop machines for employees who do not have to be mobile for their work, such as customer service representatives.
By buying thin clients, which do not include components such as hard drives, Amex can save money on technology while still providing up-to-date equipment for employees, he said.
Amex agreed a five-year, multi-million dollar deal with Compaq for the thin client systems as well as related hardware, services and support.
The deal includes Compaq's model T1010 Microsoft Windows-based thin clients and 400 Proliant servers running Intel Xeon processors.
American Express will use Citrix application software to connect the servers and the thin clients. Compaq Global Services will handle installation, configuration and support for the system.
About 80% of the units will be installed in the US, while the rest will be deployed at American Express facilities in Europe, South America and Asia.