Hi waslit
For most users, the tce directory is where all of your extensions are kept, and it must be writable.
Somewhere in the 4.x series, a CDE (CD Extensions) directory was added, this is a read only
directory to allow extensions to be included on read only media. That's the simple explanation,
if you want more details, you'll have to search the forum.
cat microcore.gz Xlibs.gz Xprogs.gz Xvesa.gz > my_xcore.gz
That command simply combines those files basically creating tinycore.gz. Most users have no
need to do this type of thing.