When one of these resource tables is full the whole system is considered to be out of resources.
Architecture.
Designed for efficiency, Windows 9x is a 32-bit OS that uses a lot of 16-bit code at the system level. 32-bit code uses more memory, and many system functions don't need the larger 32-bit memory areas. In some instances, 16-bit code will also run faster than 32-bit. The final reason for continuing with 16-bit code is for backward compatibility with older 16-bit applications. The designers of Windows 9x rightly took into the consideration that although a 32-bit architecture was available (as in the case of Windows NT), many users would still need to rely on their original 16-bit applications until such time as a viable upgrade path became available.
To ensure compatibility between 32-bit and 16-bit code, Microsoft implemented a system known as "thunking." The "thunking layer" interprets data types between 16-bit and 32-bit code implementations. The coding layer and the "thunking layer" are collected in a number dynamic link library (DLL) files. Collectively, these DLLs are known as the Win32 Application Programming Interface (API). .
Win32 API.
The most important components of the Win32 API are the Kernel, User and GDI functions. Kernel functions manage memory processes and threads. User functions control the user interface. GDI functions are used for drawing graphical images and displaying text to output devices.
The User heaps store important information about window structures, including menus. For every one window in the system, there is a WND object in the heap. Input from input devices are also managed by the User heaps, including the keyboard, interaction with sound, timer, and communications ports. An asynchronous model is used for all input and applications. This means that the device generates an interrupt to Windows, which then uses the interrupt handler to covert the interrupt into a message.