C# Definition:

     /// <summary>
    /// The MEMORYSTATUS structure contains information about the current state of both physical and virtual memory.
    /// </summary>
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    public struct MEMORYSTATUS
    {
        /// <summary>
        /// Size of the MEMORYSTATUS data structure, in bytes. You do not need to set this member before calling the GlobalMemoryStatus function; the function sets it.
        /// </summary>
        public uint dwLength;

        /// <summary>
        /// Number between 0 and 100 that specifies the approximate percentage of physical memory that is in use (0 indicates no memory use and 100 indicates full memory use).
        /// Windows NT:  Percentage of approximately the last 1000 pages of physical memory that is in use.
        /// </summary>
        public uint dwMemoryLoad;

        /// <summary>
        /// Total size of physical memory, in bytes.
        /// </summary>
        public uint dwTotalPhys;

        /// <summary>
        /// Size of physical memory available, in bytes
        /// </summary>
        public uint dwAvailPhys;

        /// <summary>
        /// Size of the committed memory limit, in bytes.
        /// </summary>
        public uint dwTotalPageFile;

        /// <summary>
        /// Size of available memory to commit, in bytes.
        /// </summary>
        public uint dwAvailPageFile;

        /// <summary>
        /// Total size of the user mode portion of the virtual address space of the calling process, in bytes.
        /// </summary>
        public uint dwTotalVirtual;

        /// <summary>
        /// Size of unreserved and uncommitted memory in the user mode portion of the virtual address space of the calling process, in bytes.
        /// </summary>
        public uint dwAvailVirtual;

    } // class MEMORYSTATUS

VB Definition:

      ''' <summary>
      ''' The MEMORYSTATUS structure contains information about the current state of both physical and virtual memory.
      ''' </summary>
      <StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Auto)> _
      Public Class MEMORYSTATUS
        ''' <summary>
        ''' Size of available memory to commit, in bytes.
        ''' </summary>
        Public dwAvailPageFile As UInt32
        ''' <summary>
        ''' Size of physical memory available, in bytes
        ''' </summary>
        Public dwAvailPhys As UInt32
        ''' <summary>
        ''' Size of unreserved and uncommitted memory in the user mode portion of the virtual address space of the calling process, in bytes.
        ''' </summary>
        Public dwAvailVirtual As UInt32
        ''' <summary>
        ''' Size of the MEMORYSTATUS data structure, in bytes. You do not need to set this member before calling the GlobalMemoryStatus function; the function sets it.
        ''' </summary>
        Public dwLength As UInt32
        ''' <summary>
        ''' Number between 0 and 100 that specifies the approximate percentage of physical memory that is in use (0 indicates no memory use and 100 indicates full memory use).
        ''' Windows NT:  Percentage of approximately the last 1000 pages of physical memory that is in use.
        ''' </summary>
        Public dwMemoryLoad As UInt32
        ''' <summary>
        ''' Size of the committed memory limit, in bytes.
        ''' </summary>
        Public dwTotalPageFile As UInt32
        ''' <summary>
        ''' Total size of physical memory, in bytes.
        ''' </summary>
        Public dwTotalPhys As UInt32
        ''' <summary>
        ''' Total size of the user mode portion of the virtual address space of the calling process, in bytes.
        ''' </summary>
        Public dwTotalVirtual As UInt32
      End Class

User-Defined Field Types:

None.

Notes:

Also see MEMORYSTATUSEX, GlobalMemoryStatus, GlobalMemoryStatusEx.