File permissions and security

You usually have to enter a username and password when you use a computer at school or work to confirm your identity. Most home computer also make you do this. There are two main reasons for doing this.

1. So that only you can access your files.

2. To protect the operating system from being modified or damaged, either by mistake or on purpose.

Anyone could write, read execute or delete a program or file on Windows PCs. Because of this, viruses could modifiy your computer to it's heart's extent. Users could also accidentally mess everything up and cause a 'blue screen of death'.

Access control list was used from Windows XP onwards, it's a much more secure system.