Compaq AlphaServer GS60 Operation Manual page 63

The 9-slot TLSB card cage is located in the upper left (front and rear) of the system
cabinet, as viewed from the front. The TLSB card cage must contain one I/O port
module, which is always installed in slot 8. The other eight slots contain a combination
of KFTHA/KFTIA I/O modules (rear only), memory, and CPU modules.
The TLSB card cage slots are numbered 0 through 3 from right to left in the front of
the cabinet and slots 4 through 8 right to left in the rear of the cabinet.
AlphaServer 8400 System 3-15