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Jan's Computer Basics:

System Software: Types

There are two basic types of operating systems, single program and multi-tasking.

Icon: Single programSingle program operating system:
Allows only one program to run at a time. If you are working working on an email and want to play a song, you must shut down the email application and open up a media player. This is annoying! Some hand-held devices like tablets and mobile phones still use this type of operating system.

Icon: Multiple programsMulti-tasking operating system:
The simplest form of operating system that allows several programs to run at the same time. The programs have to take turns with the processor. It allows the user to have email open with music playing in the background while editing a spreadsheet and a chat window open, waiting for business. Much better!!

The computer must decide how many time slices each program gets. The active (or foreground) program gets the most. Some time slices would be given to programs that are doing things but which aren't the foreground program, like downloading new email, sending a document to the printer, or synchronizing files with online storage like DropBox or Google Drive or OneDrive (formerly SkyDrive). These tasks are done in the background. A smaller number of time slices would be given to programs that are open but aren't doing anything. They need a little bit of time every now and then to see if they are supposed to do something yet.


More Terms

Multiple users of a single program Time-sharing:
Allows multiple users on a network to use the same computer (a server) or even the same program on that computer at the same time. This takes a powerful computer with the right management software.

Multiple CPUsMultiprocessing:
Using multiple CPUs at a time instead of just one CPU lets a computer assign different tasks to each CPU. Speed increases immensely. Of course cost does, too!

Dual Boot:
You can set up a computer to give you a choice of what operating system to use when it boots up. This is called dual boot even if you have more than just two choices.

Virtual machine:
VM software allows you to install additional operating systems on your computer. These run in their own window and do not realize that they are inside your original operating system. You have to install your programs to the virtual machines just as if they were running the computer on their own. You do not have to reboot the computer to switch to one of your virtual machines. This is a tremendous help when you are comparing one system to another or when you have a couple of programs that just won't run on your new, better operating system.


Common Operating Systems for Desktop Computers

Originally the operating system was created by each company that manufactured a processor and motherboard. So each operating system was proprietary, that is, unique to each manufacturer. Problem: changing to a new computer meant your software had to be replaced! Not good marketing. So there was pressure early on to standardize things so that software could be transferred to the new (and of course better!) computer. This required more standardization in operating systems.

MS-DOS iconThe winner in the PC market was MS-DOS, Microsoft's Disk Operating System, and its twin at IBM, PC-DOS, also written by Microsoft. Now it's hard to recall those days when each computer had its own unique operating system. More on DOS Commands


Icon: WindowsWindows versions from Win95 on are operating systems on their own. The earlier versions of Windows use DOS as the operating system and add a graphical user interface which will do multitasking. But with Windows 95 Microsoft released an operating system that can take advantage of the 32-bit processors.


Logo: WinXPWindows XP is an upgrade to Windows 2000. It comes in two versions - Home and Professional. The Professional version contains all the features of the Home version plus more business features, like networking and security features.


Logo: VistaWindows Vista was released in early 2007. It has higher requirements for memory and processor speed than previous versions of Windows. Vista comes in several different flavors for home and business purposes.


Logo: Windows 7Windows 7 was released in late 2009. There are several versions with differing prices.

Microsoft: Which version of Windows 7 is right for you?Icon: Off site


Windows 8 start screenLogo: Windows 8Windows 8 was released in late 2012 in several versions. Windows 8.1 was released in the fall of 2013. An update for Windows 8.1 was released in April, 2014, which is required to get future updates for Windows 8.1.

Windows 8 attempts to make the user's interaction with the operating system the same whether using a desktop computer, laptop, tablet, or smart phone. The default interface has colorful tiles for available programs and documents. It is designed to work well with a touchscreen. This was originally called the Metro interface. No more Start menu.

Microsoft: Which version of Windows 8 is right for you?Icon: Off site


Logo: Mac OS The Apple Macintosh is a multitasking operating system that was the first graphical interface to achieve commercial success. The Mac was an immediate success in the areas of graphics production, and still commands the lion's share of that market. Apple made a major marketing error when they decided to keep their hardware and software under tight control rather than licensing others to produce compatible devices and programs. While the Apple products were of high quality, they were always more expensive than comparable products that were compatible with Microsoft's DOS operating system. Apple's share of the computer market has dropped to an estimated 2.4% worldwide and 3.48% of the US market (MacWorld July 3, 2002Off site). This is an example of how a near lock on a market can be lost in a twinkling. 

Icon: Mac JaguarIcon: MacX Icon: Mac TigerThe current version is Mac OS X, which is version 10. Since January 2002, all new Mac computers use Mac OS X. Subversions are named Jaguar, Panther, Tiger, Leopard.... Most statistics show that Mac is making a comeback (Feb. 2010 - see chart at bottom of page), but the total usage is still low compared to the total number of Windows systems.


Icon: Unix UNIX is an operating system developed by Bell Labs to handle complex scientific applications. University networks are likely to use UNIX, as are Internet Service Providers. A lot of people have experience with UNIX from their college work. Many computer old-timers love UNIX and its command line interface. But all those commands are not easy to remember for newcomers. X-Windows is a graphical interface for UNIX that some think is even easier to work with than Windows 98.


Icon: LinuxLinux is an operating system similar to UNIX that is becoming more and more popular. (And it has the cutest logo!)
It is a open-source program created by Linus Torvalds at the University of Finland, starting in 1991. Open source means that the underlying computer code is freely available to everyone.  Programmers can work directly with the code and add features. They can sell their customized version of Linux, as long as the source code is still open to others. You can find more info at the Linux home site. 

By the way, the word Linux is generally pronounced with a short i and the accent on the first syllable, like LIH-nucks. On the Wikipedia page about Linux, at the lower right, there is a link to an audio file of Linus Torvalds pronouncing it in English.


Life Cycle

There are other operating systems besides the ones listed above, especially for mobile and tablet devices. New operating systems may still appear and take over the market position of the one that are popular now. Nothing in computers is so sure as change!

Microsoft, for example, has adopted a schedule for phasing out availability of its software at retail or as pre-installed on a new computer and for online support and updates. The end of extended support, also known as end of life, is very important as that is when no more security updates will be created. Windows XP reaches that stage on April 8, 2014.

Windows Life Cycle Off site

Client operating systems Latest update or service pack End of mainstream support End of extended support

Windows XP

April 14, 2009

Windows Vista

April 10, 2012

April 11, 2017

Windows 7 *

January 13, 2015

January 14, 2020

Windows 8

January 9, 2018

January 10, 2023

* Support for Windows 7 RTM without service packs ended on April 9, 2013.

** Windows 8.1 without the Update cannot get new updates. Windows 8 can still get updates.


Which is most popular?

It depends on who you ask! There is no one who can accurately report the true usage of any operating system. Various companies can report what they sold in a particular period of time and combine that info to see their "market share". Internet sites can report the operating systems of those who come to visit them. Someone might be able to estimate the "installed base" for an operating system, meaning the number of computers currently using that operating system. But no one can really tally the whole world, or even a whole country.

NetMarketShare.comOff site link:

The statistics from NetMarketShare.com are based on visits to web sites in their network of 40,000 web sites with 160 million unique visitors per month. Clearly this is not all of the web sites in the world and does not count computers that cannot access the Internet.

The static charts below show the pie charts for operating systems for the year 2013 and for April 2014. Which operating systems increased? Which decreased? Note that the April 2014 shows Windows 8.1 but the chart for 2013 does not. It was released Oct. 2013.

Pie chart: Operating Systems - 2013 NetMarketShare.comPie chart of operating systems, April 2014 from NetMarketShare.com

[Note: The blue-gray pie wedge has the highest percentage, green is second, etc. for both charts. ]

Interactive Chart from NetMarketShare.com

The arrows at the top left of the chart area change the date range, month by month. Hover over a pie wedge to see the operating system and its % of the pie.