Recently I'm encountering these two terms frequently Mainframe & Workstation. How are they different from the computers we use? I tried wiki articles but couldn't understand.
Also Terminal means just the command prompt (it's not hardware), right?
I guess these terms were used in olden days.
Mainframe was a large computer designed to be used by multiple people at the same time. It accomplished this by having several terminals plugged in via serial ports. And yes, they were physical terminals.
The terminals were incapable of doing anything other than display data that came in through the serial port and sending back data from the keyboard.
A workstation is what we're used to today. It's a computer which supports a single person, but is connected to other computers over a network.
In "olden days" terms, a workstation would have been a minicomputer, smaller than a mainframe but larger than a microcomputer. Nowdays a workstation is more or less a powerful microcomputer with lots of memory and fail-safe components.
A mainframe today is a multi-component computer (diverse CPUs, for example) to run services (server-style) for things like banking transactions and online commerce.
Of course my explanations can't be as accurate as Wikipedia's so try to hit the online free encyclopedia for more information and examples both from the old days and today.
The more modern meaning of workstation is a higher end computer, often used for graphics works, or other intensive tasks. They're typically made of more reliable components, often with Xeon/Opteron processors, ECC memory and RAID, as well as having the commercial graphics cards (Nvidia's Quadro range and ATI's FireGL cards).
However, it can be used more generally to refer to a standalone PC, rather than a thin client/terminal.
Mainframe computers are used to host servers, services, etc. A person only really logs into a mainframe to do maintenance or install new services. Workstations are computers that users will use to do work (or technically play).
Mainframes are large, contain a lot of ram, cpus, potentially network connections, etc. They are very powerful and are expected to handle a lot at one time.
Work stations are made to handle one user at a time, are less powerful, can fit into a lab or a cubical, etc.
