- PABX Private Automatic Branch EXchange
- PAD Packet Assembler and Disassembler
- PADA Packet Assembler/DisAssembler
- PAHI Public Access Internet Host
- PAIS Public Access Internet Site
- PAL Programmable Array Logic / Phase Alternating Line / Paradox Application Language
- PAP Printer Access Protocol
- PAR Positive Acknowledgment with Retransmission
- PARC Palo Alto Research Center
- PAX Private Automatic EXchange
- PBX Public Branch EXchange
- PC Personal Computer / Popup Context
- PCAMI PC Assets Manager Institute
- PCCA Portable Computer and Communications Association
- PCD Photo Compact Disk
- PCI Protocol Control Information / Peripheral Component Interconnect
- PCL Printer Control Language
- PCM Pulse Code Modulation
- PCMCIA Personal Computer Memory Card International Association
- PCS Personal Communication Services / Personal Conferencing Specification
- PCWG Personal Conferencing WorkGroup
- PD Public Domain
- PDC Primary Domain Controller
- PDF Portable Document Format
- PDIAL Public Dialup Internet Access List
- PDL Page Description Language
- PDN Public Data Network
- PDO Portable Distributed Objects
- PDP Parallel Distributed Processes
- PDS Processor Direct Slot / Personal Display System
- PDU Protocol Data Unit
- PEM Privacy-Enhanced Mail
- PEP Packetized Ensemble Protocol / Packet Exchange Protocol
- PET Personal Electronic Transactor
- PFB Printer Font Binary
- PFM Printer Font Metrics
- PGA Pin Grid Array / Professional Graphics Adapter / Programmable Gate Array
- PGP Pretty Good Privacy
- PI Popup ID
- PIC Programmable Interrupt Controller
- PIF Program Information File
- PIM Personal Information Manager
- PIN Processor Independent Network
- PINE Pine Is Not Elm
- PING Packet InterNet Gopher
- PIO Program's Input/Output
- PK Phil Katz
- PL/1 Programming Language 1
- PL/M Programming Language for Microcomputers
- PLA Programmable Logic Array
- PLE Public Local Exchange
- PLP Presentation Level Protocol
- PM Presentation Manager
- PMJI Pardon Me for Jumping In
- PMS Pantone Matching System
- PMT Photo Multiplier Tube
- PnP Plug 'n' Play
- POP Post Office Protocol / Point Of Presence
- POSIX Portable Operating System Interface for UNIX
- POST Power On Self Test
- POTS Plain Old Telephone System / Plain Old Telephone Service
- PPC Power PC
- PPD Printer Page Description
- PPN Project-Programmer Number
- PPP Point-to-Point Protocol
- PPS Pulses Per Second
- PRAM Parameter Random Access Memory
- PREP Power PC REference Platform
- PRI Primary Rate Interface
- PROFS PRofessional OFfice System
- PROM Programmable Read-Only Memory
- PSC Personal Super Computer
- PSN Packet Switch Node
- PSP Program Segment Prefixes / Presentation Services Process
- PSPDN Packet Switched Public Data Network
- PSRAM Pseudo Static Random Access Memory
- PSTN Public Switched Telephone Network
- PTP Point To Point
- PUC Public Utility Commission
- PVC Private Virtual Circuit / Permanent Virtual Circuit
- pwd print working directory
- PWM Pulse Width Modulator