CareerCup

speed and high cost are obvious answers :)

we require main memory as to access data fast and efficiently .. as any application has to be executed in most efficient manner within certain time constraints ...

also RAM means Random so data can be accessed in any order ..

any program to be executed must be in main memory.

hi kingx i appreciate your effort. I expect the answer in terms of address space generated by cpu.
can a very(very) fast hard drive replace the ram? I just want to discuss little more. I dont know the answer.

CPU has memory (registers) which is very less, I think this is the fundamental reason behind having main memory.

Speed is the sole reason why RAMs are in place. Different attributes of a RAM - like random access n all - are why the RAM speeds up program execution. Any other memory technology, which guarantees speed, can replace RAM. I don't see why speed is not acceptable as an answer. I would say that is the most prominent.

Apart from speed and random access, RAM can also be accessed at the granularity of a byte which is very crucial for programs. We do not want to do it at a SECTOR granularity for every instruction, do we?

main memory gives us the possibility of using virtual address space larger than physical address space.

That's the model of computation. Why don't you get it? It's Theory of Computation not Operating System!
Remember Von Neuman model of computation - processor + Random access memory. Read instruction(from memory)-process-write(to memory)
Technology has changed from core memory to semiconductor memory but follows the first successful model of computation.

We don't really need to have main memory in the computer if data transfers technologies (SATA/USB etc etc) were efficient back in the days and/or also CPU had more native (CACHE) memory (limitation because of transistors technology). RAM came in to the scenario just to compensate for lack of these things. To me it sounds more of a like outta box question.
Every modern computation device today is built around this concept. Imagine having a SSD drive, a cheap one, back in the days we prolly never needed RAM (Main) memory.

without M.M we can't computing any operations in computer