I'll teach you how to pick the best operating system for your older computer or laptop since most new operating systems these days run slowly on older computer, or not at all. However, there are still a few operating system like Puppy Linux, Ubuntu, and Microsoft Windows XP which run great on older computer which have slower computer parts.
The main advantage of using an operating system designed for older computers is it is usually cheaper, or free if you choose to use Linux, or you found someone selling Windows XP for under 100 dollars. Plus, you can use your older computer to use software, or play games which do not work on newer operating systems and computers which run Windows Vista, or 7. This means you can save money by not needing to buy a newer computer to play old games, do homework, browse the web, and do office work. You also might save some electricity cost since older computers use less electricity in some cases compared to the faster power hungry computers of today. This means you'll be helping the environment by not throwing out your old computer while saving electricity which is also good, and money with lower electricity costs to run a old computer.
Running Windows XP operating systems or Linux operating Systems on computer which only have 1GB of RAM, and a 1GHZ CPU instead of running Windows Vista or 7 can make your under powered computer feel super fast in some cases then running Vista, on 7 on a computer which can barely run Vista or 7, so running a older operating system on newer computers can make sense when your new computer is not powerful, or have only 1GB of RAM and a slow 1 GHz CPU.
You also might be safe for viruses designed for Windows 7, but not for XP like how Windows XP and 7 viruses can't install on Windows 98. Linux is generally immune to most viruses, and it is very hard to get infected by viruses by just surfing the web, or opening e-mails.
List of Operating Systems for Older computers
Windows XP Pro, Windows XP Home, Ubuntu Linux, and Puppy Linux are great operating system for an older computer.
Windows XP, or Linux operating systems for Slower computers
Which operating system is best for your needs for running on a slower computer.
Operating Systems Windows XP would be a better choice if you use Microsoft Office, Dreamweaver, and other software which is not available for Linux. It is also easier to install software in Windows then Linux. Windows XP also supports more hardware, so you do not have to deal with your Internet modem, printer, video card, or sound card not working. It is also easier to install.
Linux based operating systems like Ubuntu, Puppy Linux, and Linux Mint sometimes run faster on older computers, and they are free to download, and use. However, they are slightly harder to use, and install software on. In some cases some hardware like soundcards, and network cards don't work in Linux. Most Linux distros come with more software which means you do not have to buy additional software for your computer since Ubuntu comes with an E-mail client, web browser, office suite, media players, etc. Linux is also more secure since there are not as many viruses for Linux compared to Windows.
I recommend you find a computer which has 512MB of RAM, and a 1GHz CPU, and a 20GB ( Over time, the more programs you install on your computer, and files you make or download will eat up a lot of free space on your hard drive, so you should at least get a 20GB drive or use a USB drive to store your files.) or larger hard drive if you choose to run Windows XP or Ubuntu since they both can use a lot of RAM, and CPU cycles during regular use. If your computer is slower, Windows 2000, NT, and 98 are a better choice, but 2000. NT, 98 are no longer supported by Microsoft anymore, so they do not get any new Windows Updates and features like Windows XP is still supported by Microsoft until 2014.
You can run Windows XP on a slower computer with a 300 MHz CPU, 1GB of RAM, and a 5GB hard drive, but it won't be very enjoyable.
Ubuntu can run on a computer with 1GHz CPU, and 384MB of RAM, a 10 GB hard drive but if you want it to run smoothly, I recommend 1GB or more of RAM, and a CPU faster then 1 GHZ. It is best to use Ubuntu 10.04, 10.10, or 11.04 since older versions of Ubuntu which are older then Ubuntu 10.04 are no longer supported by Ubuntu, so you no longer can get Updates for old versions of Ubuntu.
Puppy Linux, Lubuntu, and Tiny Core Linux are the best operating system for your old computer if you want to run Linux on a "very" old computer which was made in the early 90s to early 2000s
PuppyLinux the best operating system for most of the slowest computer
Puppy Linux is a CD based websites which let you run on your computer on most slow computers.
Puppy Linux can run decently on a Pentium 2, 3, and 4 computer with 128MB or more of RAM. PuppyLinux comes with a web browser, a few games, programs, etc for letting you use your computer to do many tasks. PuppyLinux is easy to use, fast, and attractive.
PuppyLinux is a great way to get started and learn more about Linux for newbies since you do not need to install PuppyLinux, and it runs decently from a CD or flash drive with PuppyLinux on older computers, and run super fast on newer computers with faster computer hardware. You can even save your settings, third party software, the PuppyLinux system files to a hard drive, or even your USB Flash drive with PupyLinux installed on it, so you can load PuppyLinux faster on the next startup, or take your computer files, 3rd party programs, and settings with you to use on any computer if you choose to load PuppyLinux on a USB flash drive, or extenal hard drive.
PuppyLinux also can be a good operating system for thin clients which run programs and files off a more powerful server rather then the desktop computer.
Tiny core, and DSL Linux are also fast operating for older computers, but they are not easy to use as Puppy Linux.
Lubuntu - Best Ubuntu based operating system for older computers which previously run Windows XP
Lubuntu has been one of the best Ubuntu operating system for older computers.
Lubuntu desktop I have been using Lubuntu which is a free operating system based on Ubuntu, but uses the LXDE desktop environment on a old Dual-Core CPU computer with only 1GB of RAM, and Lubuntu has been one of the fastest Ubuntu Linux based operating systems which I ever installed on my older computer. Lubuntu barely uses any CPU resources, and only uses about 140MB of RAM after start-up. The low system resource usage of Lubuntu will make Lubuntu a great operating system for older Windows XP based computers with less RAM, and a slower single or dual core CPU. It can also be installed on 10GB or larger hard drives, so you do not need a lot of space to install Lubuntu onto your hard drive. You can also run Lubuntu from the Live CD without installing it after you start your computer from the Lubuntu Live Install CD by leaving the install CD in your computer's cd drive as your computer is starting up when you turn on the power. Installing Lubuntu is pretty simple.
I just need to follow the install instructions during the install of Lubuntu.
Lubuntu is compatible with all the same software like Firefox, Libreoffice, and Gimp which I can use in Ubuntu.
I like how fast Lubuntu starts up, and shutdown. It almost never slows down when I use it, and t rarely crashes like more heavy operating systems like Windows. Lubuntu is faster than Ubuntu because it uses the LXDE desktop environment which is a lot faster than the Unity desktop which is slower in my experience. The LXDE desktop environment also use less electricity/power than other Desktop Environment which means it will extend the life of your battery for laptops, and lower your power bill for desktops compared to using other desktop environment in Ubuntu like KDE, or Unity.
Lubuntu comes pre-installed with Firefox, Abiword, and other software which most users typically use, but I can easily install more software from the Lubuntu software center which is the program store for downloading and installing programs in Lubuntu. Plus, most programs are free like Lubuntu.