Mid-Range computers (mid-range servers) are a certain type of computers that are usually used for high end networking systems. These servers can handle large amounts of processing however they cannot process as much as a mainframe computer can. The benefit to Mid-Range computers compared to Mainframe computers however is that they are much more cheaper than a Mainframe computer, this is something that would be beneficial for start up companies or any individuals that require a server but not a large server that will set them back a lot financially.
A workstation computer is something that is often a lot better than your average personal computer/mini computer. These sorts of computers are used in working environments which require a high amount of graphical processing usage. For example a doctor may need to look at x-rays of someone and if they wanted to navigate around the x-ray they would need to use their computer, however these sorts of tasks are very graphically intensive for the computer ergo the system requires a good GPU & CPU.