How to boost Windows 7

Some people may hold out for Windows 8, but my Windows 7 laptop has started running seriously slow. It's a Sony Vaio and less than 18 months old, but now Windows takes ages to boot-up and applications are slow, even though there's nearly 50% of unused disc space.
Why does this happen. Over time Windows tends to slow down because the Windows registry and computer's hard disc get cluttered.

• The first task was to clean up the applications, by using the Programs and Features option in Windows Control Panel to uninstall things not required any more. At the same time, I cleaned up My Documents, My Pictures, My Videos, My Music, browsing history etc. Altogether I managed to get the machine's footprint down to around 55 Gbytes of used disc space.
• Next remove unwanted Windows processes. Here is a really useful site that explains how to go about this: http://www.blackviper.com/service-configurations/black-vipers-windows-7-service-pack-1-service-configurations/
• Third, upgrade memory. Although Windows 7 64-bit Edition runs in 4 Gbytes, applications benefit from more RAM. I upgraded to  8 Gbytes of RAM, using a system scanner  tool on the Crucial website.
• Finally, there is the option of using a solid state disc (SSD), which improves disc performance particularly start-up and shutdown and launching applications. I decided on 256 Gbytes to future-proof the system, and bought the data transfer kit, which allows you make a disk image of your existing Sata disc drive. My system disk was 512 Gbytes, but the imaging software had no problem transferring the data to the 256 Gbyte SSD.

RAM currently costs around £30 for 8 Gbytes and a 128 Gbyte SSD is under £80 (less if you can squeeze your operating environment in 64 Gbytes). So for little over £100 it is possible to make a big on how fast Windows runs.