The 4 basic elements of any top-level computer are:

1. Processor
2. I/O Modules
3. Main Memory
4. System Bus

1.Processor: Processor controls the entire computer. In systems, where there is only one processor, its called "Central Processing Unit" ie CPU.

2.I/0 Modules: They enable communication to and from any peripheral devices. This is done by transfer of data between the processor and I/O Modules.

3.Main Memory: It is a volatile memory, ie on switching off the computer the memory contents vanish. It is also called as the real memory or primary memory and it is used to store data and programs.

4.System Bus: It enables communication between the main memory, i/0 modules and processor.