public struct MEMORYSTATUS
{
    public UInt32 dwLength;
    public UInt32 dwMemoryLoad;
    public UInt32 dwTotalPhys;
    public UInt32 dwAvailPhys;
    public UInt32 dwTotalPageFile;
    public UInt32 dwAvailPageFile;
    public UInt32 dwTotalVirtual;
    public UInt32 dwAvailVirtual;
}

[DllImport("coredll.dll")]
private static extern int GlobalMemoryStatus(ref MEMORYSTATUS lpBuffer);

public static void GetGlobalMemoryStatus(ref UInt32 dwTotal, ref UInt32 dwAvail,
                                             ref UInt32 dwProcTotal, ref UInt32 dwProcAvail)
{
    MEMORYSTATUS status = new MEMORYSTATUS();
    GlobalMemoryStatus(ref status);

    dwTotal = status.dwTotalPhys;
    dwAvail = status.dwAvailPhys;
    dwProcTotal = status.dwTotalVirtual;
    dwProcAvail = status.dwAvailVirtual;
}

private void UpdateMemoryDisplay()
{
    /*************************************************************************/
    bool IsTotalGB = false;
    bool IsUsedGB = false;
    uint TotalRamMemory = 0;
    uint AvailRamMemory = 0;
    uint ProcTotalRamMemory = 0;
    uint ProcAvailRamMemory = 0;

    GetGlobalMemoryStatus(ref TotalRamMemory, ref AvailRamMemory,
                          ref ProcTotalRamMemory, ref ProcAvailRamMemory);

    float TotalMB = (float)((float)TotalRamMemory / (1024 * 1024));
    float UsedMB = TotalMB - (float)((float)AvailRamMemory / (1024 * 1024));

    int RamPercent = (int)((UsedMB / TotalMB) * 100.0);

    if (1000 < TotalMB)
    {
        TotalMB /= 1000;
        IsTotalGB = true;
    }

    if (1000 < UsedMB)
    {
        UsedMB /= 1000;
        IsUsedGB = true;
    }

    this.RamMemMinLbl.Text = UsedMB.ToString("0.0") + ((false != IsUsedGB) ? "GB" : "MB");
    this.RamMemMaxLbl.Text = TotalMB.ToString("0.0") + ((false != IsTotalGB) ? "GB" : "MB");
    this.RamMemPercent.Current = RamPercent;

    IsUsedGB = false;

    TotalMB = (float)((float)ProcTotalRamMemory / (1024 * 1024));
    UsedMB = TotalMB - (float)((float)ProcAvailRamMemory / (1024 * 1024));

    if (1000 < UsedMB)
    {
        UsedMB /= 1000;
        IsUsedGB = true;
    }

    this.ProcRamMemMinLbl.Text = UsedMB.ToString("0.0") + ((false != IsUsedGB) ? "GB" : "MB");

    IsUsedGB = false;

    UsedMB = (float)((float)GC.GetTotalMemory(false) / (1024 * 1024));

    if (1000 < UsedMB)
    {
        UsedMB /= 1000;
        IsUsedGB = true;
    }

    this.GCMemMinLbl.Text = UsedMB.ToString("0.0") + ((false != IsUsedGB) ? "GB" : "MB");
    /*************************************************************************/
}