Sony F900H Operation Manual page 173

Protecting saved data
To prevent accidental erasure of important setup data, use the write
protect switch on the Memory Stick.
Slide the switch right to the write protect position. It is now impossible
to write or delete data on the Memory Stick.
If you set the write protect switch to the write protect position, in step 4
when pushing the MIC/MENU knob in the previous section (page 4-87),
"MEMORY STICK LOCKED!" appears and the already saved data will
not be overwritten.
4
LOCK
Write protect switch on the Memory Stick
4-97
Chapter 4 Adjustments and Settings for Recording