The memory device context stores bitmapped images for a particular device. An application can create a memory device context by calling the CreateCompatibleDC function and supplying a handle that identifies a device context for a particular device. When the system processes this call, it creates a bitmap having a color format compatible with the original device. Because the bitmap is compatible with the given device, a memory device context is also sometimes referred to as a compatible device context.
The original bitmap in a memory device context is simply a placeholder. Its dimensions are one pixel by one pixel. Before an application can begin drawing, it must select a bitmap with the appropriate width and height into the device context by calling the SelectObject function. Once the new bitmap is selected into the memory device context, an application can begin using the device context to store images. For more information about bitmaps and bitmap operations, see Bitmaps.