How do RAM Test Applications work? C# Example?

Question

Hello,

How exactly do RAM test applications work, and is it possible to write such using C# (Example)?

Answer 1

Most use low-level hardware access to write various bit patterns to memory, then read them back to ensure they are identical to the pattern written. If not, the RAM is probably faulty.

They are generally written in low-level languages (assembler) to access the RAM directly - this way, any caching (that could possibly affect the result of the test) is avoided.

It's certainly possible to write such an application in C# - but that would almost certainly prevent you from getting direct bit-level access to the memory, and hence could never be as thorough or reliable as low-level memory testers.

Answer 2

You basically write to the RAM, read it back and compare this with the expected result. You might want to test various patterns to detect different errors (always-0, always-1), and run multiple iterations to detect spurious errors.

You can do this in any language you like, as long as you have direct access to the memory you want to test. If you want to test physical RAM, you could use P-invoke to reach out of the CLR.

However, this won't solve one specific problem if your computer is based on the Von Neumann architecture: The program that tests the memory is actually located inside the very same memory. You would have to relocate the program to test all of it. The German magazine c't found a way around this issue for their Ramtest: They run the test from video memory. In practice, this is impossible with C#.

Answer 3

As discovered by some Linux guru trying to write a memtest program in C, any such program must be compiled to run on either bare hardware or a MMU-less OS to be effective.

I don't think any compiler for C# can do that.

Answer 4

You probably can't do as good of a job testing memory from a C# program in Windows as you could from a C or Assembly language program running with no OS, but you could still make something useful.

You're going to need to use the native Windows API (via dllimpott and P/invoke) to allocate sone memory and lock it into RAM. Once you've done that, reading and writing patterns to the memory is pretty easy.

At the end of the test, you can tell the user how much of their memory you were able to test.