Thread: Difference between ROM and RAM..

ROM is not used too much in your computer. Most likely, the only ROM it has is for the BIOS, when the computer first starts up. Almost everything is stored on the hard drive, because the hard drive retains its information even when the power to it is cut out, unlike RAM, of course.

The nice thing about RAM is that it's so fast. RAM is used by currently running programs.

Depends on how you see it. RAM is slow compared to the CPU, and the HDD is slow compared to the RAM.
Lots of bottlenecks in today's systems, the biggest one being the HDD which will improve in the future.

Originally Posted by Elysia

Depends on how you see it. RAM is slow compared to the CPU

Yeah, but do you think that most CPUs have enough registers to store all of the data required to run Vista?

Today's processors have a direct bus to the memory nowadays. What's required now is faster RAM. It's too slow compared to the CPU.
Then you don't need to worry so much about enough registers to run Vista.

Mm'kay. What I meant was that RAM is fast compared to hard drives.

Run lots of programs, get a big swapfile, and you'll see what I mean . . . .

When you get down to it there are several layers of memory, each about an order of magnitude slower to access then the next. The fastest is the L1 CPU cache. Then L2 CPU cache. Then RAM. Then the hard disk virtual memory.

But yeah, your program is loaded off the hard disk and stored in RAM before it is run. Some CPUs will have a separate code bus that speeds up the execution of code by separating it from the data, but still the same RAM is used for both data and (machine) code. Both can be cached or visualized as needed.

For embedded chips programmable ROM is often used instead of a hard disk to store the code as well as any initial data needed to run.

Look, it's easy.
Data is permanently stored on the HDD. The HDD keeps its data even when the computer is powered off.
Your OS loads your program into memory when you run it. Then it's removed or discarded from memory once finished running.
There's nothing else to it. You shut down your computer, you start it up, the process repeats.

You have a source file, program.c. It is sitting on your hard drive. It is safe; turn off your computer, and it will remain on the disk.

You compile this program into program.exe. This file, too, is on your hard drive. It will not be deleted because you turned off your computer.

When you run program.exe, that instance of the program is in RAM. This instance will be lost if you shut down your computer.

But it's nothing to worry about, really. Your source code and the compiled .exe are just files on your computer. You know how files work. You can copy them, move them around, and delete them. But they don't generally delete themselves every time you reboot your computer.

Yes, the instance of program.exe will be lost if you shut down your computer. But so will Microsoft Word, if you happened to have that running. Any programs in memory, i.e. in RAM, any running programs at all, will be terminated if you turn off your computer! It's nothing to worry about, because you can always run them again.

Originally Posted by shwetha_siddu

Hai,
you told my executable code will be in RAM..but once power is off it gets erase know.

Yes, exactly. So if you were to suddenly turn the power off, you would loose whatever you were working on. Unless the program periodically auto-saves, which many programs do.

It's nothing to worry about, because you can always run them again.

Sure, if you don't mind rewriting that 10 page paper from scratch. (Just emphasizing a point)

Originally Posted by shwetha_siddu

But i am getting confuse with :-
1. what is difference between data and code?

Not much. they are both ultimately numbers. Ones and zeros as they say. But code is treated spatially by the CPU. The code is read as a series of instructions that tell the computer how to manipulate data and what code to run next.

2. Running and compiling?

Ultimately, computers can only understand one language: machine code. But machine code is hard to write, so instead we use high level languages like C. A compiler is used to "compiler" or translate C into machine code.

Running is actually telling the computer to execute a set of instructions that are written in a file. Typically this code is machine code, but it can also be script or bytecode, which has to be interpreted into machine by an interpreter. C is almost always compiled into machine code. exe files contain machine code.

3. What is Role of ROM? i heard that some instance we will transfer data from EEPROM to RAM to ROM what for this?

ROM is for embedded programing where there is no harddisk, and for BIOS that boots the OS from the hard disk initially. EEPROM is a type of programmable ROM -- ROM that has a special setting that allows it to be written to. This makes it possible to do things like update your BIOS.