XCF eXperimental Computing Facility
XD without Dividend
XDR eXternal Data Representation
XFER Transfer
XINU XINU Is Not UNIX
XL eXtra Large
XMM X-ray Multi Mirror (Espacial)
XMTR transMiTteR (o X é para trens)
XNS Xerox Network Services
XO eXecutive Officer
XOR eXclusive OR (função lógica)
XPORT Transport
XSECT cross SECTion
XTAL crysTAL (veja também XMTR)
XUI X-windows User Interface
XUV eXtreme UltraViolet (Espacial)
® Pesquisa RXA