The "s" in Win32s signifies "subset", as Win32s lacked a number of Windows NT functions, including multi-threading, asynchronous I/O, newer serial port functions and many GDI extensions. This generally limited it to "Win32s applications" which were specifically designed for the Win32s platform, although some standard Win32 programs would work correctly, including Microsoft's "3D Pinball Space Cadet" and some of Windows 95's included applets. Early versions of Internet Explorer (up to Version 5) were also Win32s compatible, although these also existed in 16-bit format. Generally, for a 32-bit application to be compatible with Win32s, it had to not use more than 16MB of memory or any extended features such as DirectX.