Xsgi  Xsgi was the Silicon Graphics (SGI) implementation of the X Window System (X11) server for its IRIX-based graphical workstations and servers. Xsgi was released in 1991 with IRIX 4.0 on the SGI Indigo workstation. Work on Xsgi began in May 1989 when Tom Paquin left IBM to join SGI to integrate the X Window System with SGI's IRIS GL interface. Paquin recruited a set of software engineers experienced in X server implementation: Jeff Weinstein, Erik Fortune, Paul Shupak, John Giannandrea, Peter Daifuku, Michael Toy, Todd Newman, Spence Murray, and Dave Spalding. Graphics hardware designed by Silicon Graphics provided accelerated rendering access through graphics hardware commands rather than memory-mapped framebuffers manipulated by the CPU. This made the Monochrome FrameBuffer (MFB) and Color FrameBuffer (CFB) device-dependent rendering layers supplied with the MIT X11 Sampler Server inappropriate for Silicon Graphics hardware. Jeff Weinstein developed the No FrameBuffer (NFB) device-dependent rendering layer to support the Silicon Graphics style of hardware access. SCO later incorporated the NFB layer in its X server porting layer. Silicon Graphics hardware included overlay planes to provide a hardware overlay. Initial efforts by Todd Newman to implement overlay plane support in Xsgi eventually led to Peter Daifuku's "fully functional" support for overlay planes. Daifuku separated the notion of a window's visibility clipping region from the window's renderable clipping region. Previously the MIT X sample server treated these two clipping regions as being the identical region. Xsgi advertises overlay planes as X11 visuals with their overlay characteristics described by the SERVER_OVERLAY_VISUALS convention. Erik Fortune developed the X keyboard extension (XKB) for Xsgi. Xsgi supported the X11, IRIS GL, OpenGL, Display PostScript, and PEX PHIGS rendering models.