In TU100 I have learnt that there're 4 generations of computers, the first one being from around WW2 these are the computers which use thermionic valves, such as the Colossus which was used to break the codes by the germans.
This machine used paper tape for data input, for the output it would send it to an electric typewriter.
The public did not know about this machine until it went on to the public domain in the 1970's, it is now an attraction at Bletchley Park, Milton Keynes, the original Colossus was decommissioned at the end of the war and dismantled and destroyed, but a working replica was produced which stands in its place today.
Another example of the first generation computers was the ENIAC (Electronic Numerical Integrator and Computer) this was built by the University of Pennsylvania this also used thermionic valves the same as Colossus. This computer weighed 27 tonnes and occupied 63 square metres and was 26 metres long.
It was used to for lengthy calculations for the US Military. The ENIAC was not very user friendly like computers are today it used to take weeks and weeks to set up a program and errors could occur and then you would have to start again. You could not save your program state either and it was very unreliable, it was under repair more than it was working.
On a side note, Thermionic valves were very delicate and used to break a lot, they discovered that if you left the machine on then the valves would last longer.
The Second generation of computers were those that used transistors, these came out in the late 1950's. These computers where still very large and still very expensive for example one of the first computers that had this transistor technology was IBM's 608 at a price of $83,000 that was a huge outlay for most companies. Most of the computers of course as I mentioned above they were large but a lot smaller than the Colossus and the ENIAC, some of these transistor based computers were about the size of wardrobes.
These new transistors were a few millimetres in diameter so they were less than a thousandth of the volume of the thermionic valve. Transistors were much cheaper to manufacture than valves and of course they were more reliable as well. the switching speeds were also much faster than that of the valves.
The third generation of computers saw rise of the integrated circuit (IC) this was also known as 'chip' or 'silicon
chip' with these computers punchcards and tape were the thing of the past they were no longer used for input and output instead they had peripherals known as 'keyboards' for the input and for the output they had 'monitors' so for the out put of data they no longer needed paper printouts, also in this generation the Floppy disk was introduced, The IC was much faster in terms of processing speed than any of it's predecessors. Many minicomputers and mainframes moved onto this technology. These silicon chips were made from several components integrated onto a single chip. The IC computers were also able to talk to each other through telephone lines these were called terminals and could be distributed across the country and connected to a single shares computer.
The fourth generation of computers are basically the computers of today - the microprocessor (CPU) all computers and devices including Smart phones, tablets laptops, set top boxes, and even televisions have microprocessors, the microprocessor came out in the late 1970's, it has reduced running costs and manufacturers are able to make in large numbers. With the rise to the microprocessor, home computers were very much a reality, as these processors were cheaper to make and as I said before companies to make large amounts of them every day people started to have a personal PC in their home.