Buying new vs Upgrading your old Computer

The world of IT and computing as come to a point where innovation,new developments,upgrades etc as become the trend.More often than not,most if not all gadgets or equipments only have a lifeline of few months,for them to become old or not good enough.
This as made competition become the in-thing among vendors and this as also affected the pocket or purchasing power of consumers.It as become very common among the consumers of the following items in particular:Computers(Laptop.Desktop,servers and other components),Mobile and Fixed line phones,Motor Vehicles e.t.c
You've come to a point where you need to upgrade to a higher spec of computer but you don't have enough cash to make the change.I have over time used a method to overcome this issue,thereby saving money and getting the higher grade that i want.I will for now limit this to Computers.
The basic components of most systems are:OS,Screen size,Weight,Optical Drive,Memory,Hard disk & Processor.Among all this,the basic ones which determine prices are:Optical Drive,Memory,Hard Disk and Processor.
The catch here is this:If i have a system of about $250 with obviously a lower spec and a new or a higher spec one which goes for $450.what i readily do is to buy (Optical drive,Memory & Hard drive) of a higher spec and install on the old/lower spec system.this normally cost me around $80 - $120,which comes to about $320 - $370,therefore,saving about $80 - $130
This is a simple tactics which could save from hundreds to thousands of dollars on a budget.
A check on the net will get you more than enough information on the above subject.
One of the main considerations on the above mechanism is to know where this components are located and how to fixed them.
If you'd like to send questions to me, please feel free to visit my Website and I'll be happy to answer your queries, or point you in the right direction.
Good luck!