A computer system (for example a blade server system) includes a connection framework for receiving at least two replaceable units (e.g., service processor units). Where a first replaceable unit is provided in the connection framework, the first replaceable unit can, on a second replaceable unit being received in the framework, allow restricted use of a default admin user login without a password for up to the end of predetermined period following receipt of the second replaceable unit. On receipt of an admin login with a configured password during the period, or on expiry of the period, the system can revert to normal operation.