...Our body couldn’t function without our brains. The brain tells the various pieces of our body how to work and how to interact. Without a brain, we wouldn’t be able to do anything at all. An operating system is kind of like the brain of a computer. You have a bunch of hardware like the CPU tower, the monitor, and the keyboard, but without a CPU, they can’t do anything but power up and turn on. The operating system organizes files and lets the hardware know what it should do. In the early days of computers, there was just one operating system. As computers progressed, the OS turned into MS-DOS, but computers really weren’t capable of doing much without software. Then Bill Gates came along. With the founding of Microsoft, the computer operating system came into its own and brought computers to new levels of functioning and technology. Although the brand names of operating systems are few, they do perform different tasks depending on the requirements of the computer user. While the dominant OS today would be Microsoft Windows, there are other types of operating systems that offer different features. Those would include Linux, UNIX, and OS X. In our technological age, there are operating systems in more than just computers. Many of the sophisticated new cell phones have their own operating systems, and wireless access points have their own OS to provide wireless internet to customers. In fact, the computer in a cell phone today is more powerful than a computer was twenty years ago...

...Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux. In any device that has an operating system, there's usually a way to make changes to how the device works. This is far from a happy accident; one of the reasons operating systems are made out of portable code rather than permanent physical circuits is so that they can be changed or modified without having to scrap the whole device. For a desktop computer user, this means you can add a new security update, system patch, new application or often even a new operating system entirely rather than junk your computer and start again with a new one when you need to make a change. As long as you understand how an operating system works and know how to get at it, you can in many cases change some of the ways it behaves. And, it's as true of your cell phone as it is of your computer. So, essentially, when you turn on your computer, the first program is a set of instructions kept in the computer’s read only memory. These instructions examine the system hardware to make sure everything is functioning properly. This power-on self test check the CPU, the memory, and the basic input/output systems (BIOS) for errors and stores the result in a special memory location...

...Internal security can be thought of as a way to protect the computer’s resources from the programs concurrently running on the system. Most operating systems set programs running natively on the computer’s processor. That brings on the problem of how to stop these programs from doing the same task and having the same privileges as the operating system which is just a program too. Processors used for general purpose operating systems are automatically blocked from using certain hardware instructions such as those to read or write from external devices like disks. Instead, they have to ask the privileged program, or operating system kernel) to read to write. The operating system, therefore, gets the chance to check the program’s identity and allow or refused the request. An alternative strategy available in systems that don’t meet pre-set requirements is the operating will not run user programs as native code. Instead, they either emulate a processor or provide a host for a “p-Code” based system such as Java. Internal security is especially important with multi-user systems as it allows each user of the system to have private files that the other users cannot tamper with or read. Internal security is also vital if auditing is to be of any use since a program can potentially bypass the operating system without bypass auditing...