Internet is a world-wide / global system of interconnected computer networks.
Internet uses the standard Internet Protocol (TCP/IP)
Every computer in internet is identified by a unique IP address.
IP Address is a unique set of numbers (such as 110.22.33.114) which identifies a computer location.
A special computer DNS (Domain Name Server) is used to give name to the IP Address so that user can locate a computer by a name.
For Example, a DNS server will resolve a name http://www.tutorialspoint.com to a particular IP address to unique identify the computer on which this website is hosted.
Internet is accessible to every user all over the world.
Intranet
Intranet is system in which multiple PCs are networked to be connected to each other.
PCs in intranet are not availble to the world outside of the intranet.
Usually each company or organizations have their own Intranet
network and members/employees of that company can access the computers
in their intranet.
Each computer in Intranet is also identified by a IP Address which is unique among the computers in that Intranet.
Similarities in Internet & Intranet
Intranet uses the internet protocols such as TCP/IP and FTP.
Intranet sites are accessible via web browser in similar way as
websites in internet. But only memebers of Intranet network can access
intranet hosted sites.
In Intranet, own instant messengers can be used as similar to yahoo messenger/ gtalk over the internet.
Differences in Internet & Intranet
Internet is general to PCs all over the world where Intranet is specific to few PCs.
Internet is wider access and provides a better access to websites to large populcation where as Intranet is restricted.
Internet is not as safe as Intranet as Intranet can be safely privatized as per the need.
