There are a lot of different things that affect the speed of a computer. The brand type probably affects speed mostly because of the type of hardware. Different computer makers will use different layouts, parts, and materials to construct the computer. If two different processors are used, their efficiency and speeds will differ as well. In addition, each computer has a clock that drives its processor. A 500 MHz clock, for example, makes the computer do 500,000,000 operations per second, while a 100 MHz clock only makes the computer do 100,000,000 operations per second. That means that the first computer is 5 times faster than the second if they are identical in every other way.
Each computer also has a different way of computing things. Different algorithms for storage and retrieval can affect the speed, along with many other factors.
I'm not quite sure what you mean by data type, though- do you mean the way in which data is stored in the computer?
Good luck with your project!
Nature uses only the longest threads to weave her patterns, so that each small piece of her fabric reveals the organization of the entire tapestry.