| A | B |
| NLM | Netware Loadable Module |
| NM | Nanometer |
| NNTP | Network News Transport Protocol |
| NT | New Technology |
| NTFS | New Technology File System |
| NTP | Network Time Protocol |
| OCx | Optical Carrier |
| OS | Operating Systems |
| OSI | Open Systems Interconnect |
| OSPF | Open Shortest Path First |
| OTDR | Optical Time Domain Reflectometer |
| OU | Organizational Unit |
| PAP | Password Authentication Protocol |
| PC | Personal Computer |
| PCI | Peripheral Component Interconnect |
| PCMCIA | Personal Computer Memory Card International Association |
| PDC | Primary Domain Controller |
| POP3 | Post Office Protocol Version 3 |
| POTS | PLain Old Telephone System |
| PPP | Point-to-Point Protocol |