When you log into your UNIX account on CMGM or PMGM, you are in your home directory.
Within your home directory are files that are owned by you. You have control over these files. You can delete them, change their permissions, allow others to read them, or you can edit them yourself.
Most users are limited to 5-10 Megabytes of disk storage space. Research groups are limited to 50 Megabytes total.
If you need additional space, you can purchase a 2Gb disk for $600. Some research groups have done just that.
There is also temporary space in the /tmp subdirectory. Any file that has remained in that directory for more than a week without change, will be deleted.