Siemens simatic PC 577 Operating Instructions Manual page 119

Servicing and maintenance
10.2 Removing and installing hardware components
3. Remove the 4 screws (1) while securely holding the retaining frame (2).
Figure 10-7 Removing the hard disk
SIMATIC Panel PC 577
10-21
Operating Instructions, Release 04/2006, A5E00798484-01