X

XBA             Registers. The operational registers of the CDC 6600, where 
                X,B and A refer to accumulator, index and address registers 
                respectively.
XDI             eXternal Device Interface. A series of calls made by the 
                DESQview multitasker on various "interesting" events, which
                may be intercepted by programs which wish to keep track of
                the current system state.
XDMCP           X Display Manager Control Protocol.
XDR             eXtended Data Representation. XDR is a way of normalizing
                data representation among a large number of otherwise
                incompatible operating systems.
XGA             eXtended Graphics Array. A color video standard introduced by
                IBM in 1991 that supports 1024 x 768 pixels with 256 colors
                or 640 x 480 pixels with 65,536 colors.
XMS             eXtended Memory Specification. A specification devised by
                Microsoft which allows multiple programs to share extended
                (above 1 megabyte) memory and noncontiguous memory above 640K.
                See also UMB.
XNS             Xerox Network System.
XPT             eXternal Page Table.
XSMD            Extended Storage Module Drive (interface).


Y

YSE             Yorktown Simulation Engine. The YSE is a special-purpose 
                parallel processor, built at IBM to speed the development of 
                large computers by providing rapid simulation of the large 
                network of logic gates that such machines represent.
YUV             A color specification mechanism used in NTSC-type color 
                television signals.  Y represents luminance (overall 
                brightness, the only part of the signal used by black-and-
                white televisions), while U and V are chrominance (color) 
                information.  Also called YIQ.  See also RGB.
                

Z

Z               Zero-result flag. The status flag that a CPU sets when the 
                result of an operation is 0.
