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Actually, there are many sides affecting the computer performance. So we can improve the system performance in many ways. For example, you can pay to add a SSD or spend time to delete unwanted programs and disable unnecessary startup programs. You can view different methods and detailed steps here http://blog.doofix.com/how-to-speed-up-the-computer-like-a-new-one/
I got remarkable improvements on a much older laptop, an IBM Thinkpad X41. Nice and compact, but Microsoft said it was too old, too limited even to upgrade to Windows 7 from XP. I made the biggest possible changes in software (new OS) and hardware (HD to SSD).
Now running Xubuntu Linux. It's fast! Boots up and shuts down in seconds. It's a huge, dramatic improvement over Ubuntu for my purposes, admittedly lightweight, no intense graphics, no games. Email to my Yahoo account via Thunderbird runs much better too. Watching web video is fine. XP was a pain. Windows 7 on a friend's laptop also seems clunky by comparison.
For hardware, I replaced the original hard drive with an SSD. The hard drive had been slightly damaged (too vulnerable for a portable device!) when I dropped the computer onto the floor, but still worked OK. Now the only moving part is the tiny fan inside.
It's been computer life extension!