what for nobody:nogroup, lp:lp, tc:floppy?

[nick65go]

Could you please tell me the trick about few default user:group in tinycore?

===/etc/group; The 'x' means that password is stored in /etc/gshadow
group:password:group_ID:users_CSV
root:x:0:
lp:x:7:lp
nogroup:x:65534:
staff:x:50:

===/etc/gshadow; password !(locked) or * means group members do not need the password;
group_name:encrypted_password:administrators_CSV: users_CSV
root:*::
nogroup:!::
staff:!::
floppy:!::tc

===/etc/passwd; The 'x' means that the user’s password is stored in /etc/shadow.
user:x:user_ID:group_ID:user_name:use_home_folder:user_shell
root:x:0:0:root:/root:/bin/sh
lp:x:7:7:lp:/var/spool/lpd:/bin/sh
nobody:x:65534:65534:nobody:/nonexistent:/bin/false
tc:x:1001:50:Linux User,,,:/home/tc:/bin/sh

1.So, group floppy is not in /etc/group, but only in /etc/gshadow. why?
What is this tc:floppy used for? when?

2. So, group lp is in /etc/group, but not in /etc/gshadow. Why?
What is this lp:lp used for? And when because is disabled?

3. What test/debug is this nobody:nogroup used for? And when because is disabled?

The hints are rely welcome. Thanks

[curaga]

lp/floppy are likely unused remainders. Nobody (/nogroup) is a standard user, it's used everywhere where something is specifically nobody's. For example, NFS uses it if it can't map an uid.