You are right Sup V has 64-MB onboard Flash memory (in addition to removable Flash memory)
The Flash port accepts a Type 1 compact Flash card. You can use it for file transfer tasks such as loading a new software image. The Flash card is optional and can be obtained from third-party suppliers.
For more information, refer to Using the Compact Flash on the Catalyst 4000 Family Supervisor Engine III and IV at the following URL: