Difference between ROM and RAM..

Dear All,
As per as my knowledge difference between ROM and RAM is that:-

ROM:- Read Only memory..all I/O related files will be stored and operating system files are stored...which can't be modified

RAM:- Random access memory...data which can be repeatedly access by processor stored in this memory..

Where is my final Executable C code will be stored?
if your answer is RAM...RAM is volatile memory(Once power is off then data gets lost)...i am getting some kind of confuse can anybody clerify my question?

Thanks in Advance

Your executable is in RAM while it's running, certainly. But that's memory; that's not storage. All that stuff on your disk is just that: on disk.

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.

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Originally Posted by Elysia

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

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

:)

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.

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Originally Posted by tabstop

Your executable is in RAM while it's running, certainly. But that's memory; that's not storage. All that stuff on your disk is just that: on disk.

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Hai,
you told my executable code will be in RAM..but once power is off it gets erase know..do have any back up for this..do you know any good site in google to read this memory operations clearly...

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.

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Originally Posted by shwetha_siddu

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

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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.

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

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

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Originally Posted by dwks

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.

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But i am getting confuse with :-
1. what is difference between data and code?
2. Running and compiling?
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 used to get the computer operational when it powers on. It basically tells the computer how to find out what it has and what to do.

Your program will not be utilizing ROM unless your are writing a super low level program to load the ROM with new data.


Compiling is basically the act of taking your code (the stuff you write) and translating it from a human readable format to a machine readable format.


Code is basically instructions to the CPU. Data is the stuff it does those instructions onto. So a variable is data as is a text file. Code can also be treated as data but in practice that is rarely done on purpose.

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Originally Posted by shwetha_siddu

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

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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.

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2. Running and compiling?

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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.

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

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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.

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

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

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I just knew someone was going to say that. ;)

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2. Running and compiling?

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As Thantos said, when you compile a program, you basically turn the human-readable source code (in C) that you wrote into a machine-readable executable (in machine code) that the computer can run.

When you run a program, you tell the CPU to start at the beginning of the program and execute the instructions contained therein. When you start Word, you're running a program.

[edit] "It has more"? :) More what? Don't leave us hanging! :p [/edit]

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Originally Posted by shwetha_siddu

But i am getting confuse with :-
1. what is difference between data and code?
2. Running and compiling?
3. What is Role of ROM? i heard that some instance we will transfer data from EEPROM to RAM to ROM what for this?

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1. I don't know. Is there a difference between data and code?

2. Running a program executes a bunch of commands. Compiling takes stuff we can read (C, for instance) and turns it into commands the computer can read (1's and 0's) and maybe execute later.

3. This would happen when you're making hardware, I guess; if you have some spare silicon running around, and want to make a chip and put some ROM on it, you would need to get it on there somehow. My rough estimate is that at least 9999 C programs out of 10000 would never get here.

Aha! I have an analogy all ready now:

When you write code, you're drawing a plan for a mould on paper. When you create this mould out of plastic, you're compiling the program. When you use this mould to create lots of little moulded objects out of plasticine, which you can then flatten out and use again, you're running the program . . . . :p

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Originally Posted by shwetha_siddu

But i am getting confuse with :-
1. what is difference between data and code?
2. Running and compiling?
3. What is Role of ROM? i heard that some instance we will transfer data from EEPROM to RAM to ROM what for this?

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1. Code is something that the processor can (and should) execute as instructions - it's the add, sub, mov, jmp instructions that make a program work. Data is anything the program needs that ISN'T code [although some people will separate data into subcategories, and I'm sure your tutor will start asking you what the heap and stack is at some point in the future, but I won't forgo the question by answering it here].

2. Running or executing is when the processor "runs" the program, that is, the processor is performing whatever task it has been told to do in the code. Compiling is the phase where the compiler (a program written for this purpose) is translating the human-readable code, say

Code:

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int main()
{
  printf("Hello, World!\n");
  return 0;
}

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into machine-readable instructions (code and data). The compiled code is called "executable", and in windows has (usually) the extension .exe.

3. ROM in a PC is not used for anything other than the initial startup (where it loads the first bit of program code from the hard disk, which then loads the rest of the operating environment) and last steps of shutdown.

If you have a mobile phone or other embedded device, where there is no hard-disk, then the executable code + data for that device is normally stored in some form of ROM - it can be a traditional ROM that is programmed at the time of manufacturing - these are the cheapest ones, or it can be a EPROM (old technology now) or a EEPROM, such as Flash-ROM's. These are erasable and can be reprogrammed. EEPROM can be reprogrammed in situ in the machine, whilst EPROMs may need for example UV-light to be erased.

Some embedded systems use ROM for "Execute in place", meaning that the processor executes directly from the ROM itself. Other embedded systems, for performance reasons, move the code from the ROM to the RAM during the first part of the startup (obviously, the first execution happens from ROM).

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Mats