Memory Benchmark that is faster to code than to find an app. Gives 24.9 on a machine with 25.6 theoretical limit on a single thread.

MemoryBenchmark.cs

public class MemoryBenchmark
{
    public static void Run()
    {
        const long sizeGb = 2L;
        const long arraySize = sizeGb * 1024 * 1024 * 1024;
        const int elementSize = sizeof(long);
        long[] data = new long[arraySize / elementSize];

        Console.WriteLine($"Allocated {sizeGb}GB array");
        Console.WriteLine("Writing to array...");

        var stopwatch = Stopwatch.StartNew();
        for (long i = 0; i < data.Length; i++)
        {
            data[i] = i;
        }

        stopwatch.Stop();
        double writeTimeSeconds = stopwatch.Elapsed.TotalSeconds;
        Console.WriteLine($"Write Time: {stopwatch.ElapsedMilliseconds} ms");

        Console.WriteLine("Reading from array...");

        stopwatch.Restart();

        long sum = 0;
        var rounds = 100;
        const int prefetch = 128;
        const int step = prefetch / elementSize;

        for (int r = 0; r < rounds; r++)
        {
            for (long i = 0; i < data.Length; i += step)
            {
                sum += data[i];
            }
        }

        stopwatch.Stop();
        double readTimeSeconds = stopwatch.Elapsed.TotalSeconds;
        Console.WriteLine($"Read Time: {stopwatch.ElapsedMilliseconds} ms");

        // Calculate throughput
        double writeThroughput = arraySize / writeTimeSeconds / (1024 * 1024 * 1024); // GB/s
        double readThroughput = rounds * arraySize / readTimeSeconds / (1024 * 1024 * 1024); // GB/s

        Console.WriteLine($"Write Throughput: {writeThroughput:F2} GB/s");
        Console.WriteLine($"Read Throughput: {readThroughput:F2} GB/s");
    }
}

Usage.cs

var t1 = Task.Run(() => MemoryBenchmark.Run());
var t2 = Task.Run(() => MemoryBenchmark.Run());
// var t3 = Task.Run(() => MemoryBenchmark.Run());
MemoryBenchmark.Run();
t1.Wait();
t2.Wait();
// t3.Wait();