It all started with computer hardware in about 1945s. Computers were using vacuum tube technology. Programs were loaded into memory manually using switches, punched cards, or paper tapes.As time went on, card readers, printers, and magnetic tape units were developed as additional hardware elements. Assemblers, loaders and simple utility libraries were developed as software tools. Later, off-line spooling and channel program methods were
Finally, the idea of multi-programming came. Multi-programming means sharing of resources between more than one processes. Now the CPU time was not wasted. Because, while one process moves on some I/O work, the OS picks another process to execute till the current one passes to I/O operation.
With the development of interactive computation in 1970s, time-sharing systems emerged. In these systems, multiple users have terminals (not computers) connected to a main computer and execute her task in the main computer.
Another computer system is the multiprocessor system having multiple processors sharing memory and peripheral devices. With this configuration, they have greater computing power and higher reliability. Multiprocessor systems are classified into two as tightly-coupled and loosely-coupled (distributed). In the former one, each processor is assigned a specific duty but processors work in close association, possibly sharing the memory. In the latter one, each processor has its own memory and copy of the OS.
Use of the networks required OSs appropriate for them. In network systems, each process runs in its own machine. The OS can access to other machines. By this way, file sharing, messaging, etc. became possible.
In networks, users are aware of the fact that s/he is working in a network and when information is exchanged. The user explicitly handles the transfer of information.
Distributed systems are similar to networks. However in such systems, there is no need to exchange information explicitly, it is handled by the OS itself whenever necessary.