Difference between Linux and UNIX ?

For me the main difference between Linux and UNIX is  - Free v/s Money.

UNIX is money oriented product that BIG companies uses :)

IBM AIX and Sun Solaris and HP-UX all are UNIX operating systems.

Most UNIX systems are commercial in nature.

Linux compliance the POSIX standards so it cab also be considered as UNIX.

In Linux world, Linux is nothing but just a kernel. The open communitiy makes distribution based
on this kernel and gives different name to market their identity.

Linux is Free. Few distribution is freely available via internet.
Linux is user-friendly. It makes it easy to install sound card, flash players, and other desktop goodies
Linux comes with firewall - iptalbes/ipchains(older version of firewall)
Linux comes with Backup and Recovery software.
Linux supports ext2,3,4, ResierFS File Systems where as UNIX has different file system depends on the distro.

Distro has different Startup scripts location:Linux - /etc/init.d/
AIX - /etc/rc.d/init.d/
Solaris - /etc/init.d/
HP-UX - /sbin/init.d/
SUSE - /etc/rc.d/init.d/

UNIX distro: 1) Oracle Solaris
2) HP-UX
3) IBM AIX
4) Mac OS

Linux Distro: 1) Redhat
2) Fedora
3) SUSE
4) Ubuntu
5) Debian