What are those large files in folder "user--my document--ArcGIS--default.gdb"

Hi everyone,

I install ArcGIS 10 in C://program file(X86) 2 months ago. Today I found my C disk is nearly full (80+G used). Then I found there are some really large file (10G or several hundred M) store in this folder "C--user--my document--ArcGIS--default.gdb", under names like "a00000011.gdbtable", "a0000016.gdbtable" and "a00000011.blk_key_index.atx", ect.

Does anyone know what are these files? Can I delete them or move them to another disk? Cause they are too large.....

Thanks a lot!

Mo