- R&D Research & Development
- RAD Rapid Application Development
- RAID Redundant Array of Inexpensive Disks
- RAM Random Access Memory
- RARE Reseaux Associes par la Recherche Europeenne
- RARP Reverse Address Resolution Protocol
- RAS Remote Access Services
- RAT Register Alias Table
- RBOC Regional Bell Operating Companies
- RBSE Repository-Based Software Engineering
- RC Routing Control
- RCP Remote Copy Program
- RD Referenced Documents / Received Data / Route Descriptor
- RDA Remote Database Access
- RDBMS Relational DataBase Management System
- REM Ring Error Monitor
- REPOUT REPeater OUTput to Port
- REXX Restructured EXtended EXecutor
- RFC Request For Comments
- RFI Radio Frequency Interference
- RFP Request For Proposal
- RFS Remote File System
- RGB Red Green Blue
- RH Request Header / Response Header
- RHost Remote Host
- RI Ring Indicator / Routing Information
- RII Routing Information Indicator
- RIP Remote Imaging Protocol / Routing Information Protocol
- RIPE Reseaux IP Europeenne
- RISC Reduced Instruction Set Computer
- RJ Registered Jack
- RJE Remote Job Entry
- RLA Remote LAN Access
- RLC Run Length Coding
- RLIN Research Library Information Network
- RLL Run-Length Limited
- rn readnews
- ROB ReOrder Buffer
- ROFL Rolling On Floor Laughing
- ROI Return On Investment
- ROM Read-Only Memory
- ROSE Remote Operations Service Element
- rot13 rotate 13
- ROTFL Rolling On The Floob Laughing
- RPC Remote Procedure Call
- RPS Ring Parameter Service
- RR Register Routine
- RRF Retirement Register File
- RSAC Recreational Software Advisory Council
- RSI Repetitive Stress Injury
- RSN Real Soon Now
- RSX Real-time resource-Sharing EXecutive
- RT Routing Type
- RTC Real-Time Controller
- RTF Rich Text Format
- RTFM Read The Fine Manual
- RTM Run-Time Manager
- RTMP Routing Table Maintenance Protocol
- RTPC RISC Technology Personal Computer
- RTS Request To Send
- RTT Round-Trip Time
- RU Request Unit / Response Unit
- RUIP Remote User Information Program