If you have an old PC laptop that is slow to start up and slow to open files, but is otherwise fine, you don't have to junk it. We have a four year old laptop with a 1.3 GHz i3-380M processor that was getting slow. I expanded the memory to 6GB a few years ago, an inexpensive (under $75) and easy way to speed it up. However, it was still slow and it would cost about $350-$500 to get an equivalent laptop today and I would have to get used to Windows 8.
So I replaced the 320GB hard drive with a $100 256GB Solid State Drive (SSD) and the performance has improved dramatically. The replacement took about 20 minutes with a screwdriver to do the replacement and about 30 minutes to reload Windows 7. There is a large choice of SSD brands and sizes, you can even get a 1TB drive for under $500 if you want.
The replaced hard drive can be used as a backup drive if you purchase an inexpensive hard drive enclosure for the old drive for about $10-$15. Putting the drive in the enclosure will take about 5 minutes. Voila, a 320GB USB-powered external drive.
If you have a MAC laptop, none of this applies. Putting an SSD in a MACbook is possible, but is much more complicated due to the proprietary drive form factor and Apple's efforts to stop you from opening the case (special screws, complicated assembly..).