gistfile1.cs

// http://channel9.msdn.com/Events/Build/2013/4-329

int N = 1000;
var A = new int[N,N];
var B = new int[N, N];
var C = new int[N, N];
var random = new Random();
for(int x = 0; x < N; x++)
{
    for(int y = 0; y < N; y++)
    {
        A[x, y] = random.Next();
        B[x, y] = random.Next();
        C[x, y] = random.Next();
    }
}

var watch = new Stopwatch();
watch.Start();

for (int i = 0; i < N; i++)
    for (int j = 0; j < N; j++)
        for (int k = 0; k < N; k++)
            C[i,j] += A[i,k] * B[k, j];

watch.Start();

Console.WriteLine("Time: {0}ms", watch.ElapsedMilliseconds);


watch.Reset();
watch.Start();

// 60% Faster than the loop above!
for (int i = 0; i < N; i++)
    for (int k = 0; k < N; k++)
        for (int j = 0; j < N; j++)
            C[i, j] += A[i, k] * B[k, j];

watch.Start();

Console.WriteLine("Time: {0}ms", watch.ElapsedMilliseconds);