| Abbreviations Starting With C (not actively used) | |
| C2D | Character to Decimal |
| C2X | Character to Hexadecimal (REXX language function) |
| CADD | Computer Aided Design and Drafting |
| CBEMA | Computer & Business Equipment Manufacturer's Association (replaced by ITIC) |
| CCFL | Cold Cathode Fluorescent Lamp (replaced by LED bulbs/lamps) |
| CCSD | Cellular Circuit Switched Data |
| CDC | Century Date Change (19xx to 20xx or Y2K, 20xx to 21xx and so on) |
| CDDA | Compact Disc Digital Audio |
| CDPD | Cellular Digital Packet Data (CDPD service retired in 2005) |
| CDTV | Commodore Dynamic Total Vision |
| CDXA | Compact Disc Extended Architecture |
| CEO | Celestial Ephemeris Origin ( astronomy) |
| CFI | CAD Framework Initiative (renamed to Si2) |
| CFM | Cold Fusion Metafile |
| CHS | Cylinder Head Sector (HDD) |
| CIM | Computer Input by Microfilm |
| CIX | Commercial Internet eXchange |
| COFF | Common Object File Format (replaced by ELF) |
| COM | Computer Output to Microfiche/Microfilm |
| CPHB | Computer Protocol Heart Beat (IANA number 73) |
| CPM | Cards Per Minute (punch card based systems) |
| CPS | Characters Per Second |
| CGMS-A | Copy Generation Management System - Analog |
| C-VGA | Color VGA |
| CD-I | Compact Disc Interactive |
| CP/M | Control Program/Monitor (later known as Control Program for Microcomputers) creator - Gary Kildall |
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