The latter are used for RAM and frame buffer cards. On the display, it had to manipulate pixels in the frame buffer. This allows the manufacture of simpler display devices without frame buffer memory. Graphics capability was provided by two frame buffer modules, the monochrome and color frame buffer. The 2600 does not have a frame buffer. For entry graphics, the 8-bit color frame buffer comes in three versions. Stencil and Z-buffers are part of the frame buffer, coupled to the color buffer. Frame buffer memory operated at 150MHz and used 64-bit bus. The X11 programming interface XShmGetImage is used to retrieve the frame buffer pixel data. In general, this is a large pixel matrix or "frame buffer". The OpenGL/DirectX programmer then renders to a very large frame buffer for output. Early video data storage units (RAIDs) fed custom frame buffer systems with large memories. In particular the canvas may be the frame buffer for a computer display. The term "frame buffer" is thus often used interchangeably when referring to this RAM.