| swp | Vim Swap Data |
| swp | General Swap File |
| swq | SWAT Stream Water Quality Input Data |
| swr | SageWorld Anti-Hacker Program Output |
| swsd | Sodera Spectrum Data |
| swv | Sidewinder Game Voice Settings |
| swzk | SWiSH Wizard Data |
| sxg | Stradx Segmentation Data |
| sxr | Stradx Registration Data |
| sxt | Formula Graphics Script |
| sxv | Action Repeater File |
| sxv4 | SuperSTAR Database |
| sy | Simplexety Data File |
| sy1 | AMI Pro Smartpix Symbol Library |
| syc | Network Associates Sniffer Capture |
| syd | SYSTAT Data File |
| syg | SYSTAT Graph |
| syl | Symbolic Link Spreadsheet |
| sylk | Symbolic Link Spreadsheet |
| sym | VariCAD Symbol Library |
| syn | TextPad Syntax File |
| sync | Apple ColorSync Data |
| syncdb | iTunes Sync Database |
| syncml | Open Mobile Alliance SyncML Data |
| syr | Xilinx XST Synthesis Report |
| sys | Microsoft SQL Server Data Replication System Table Data |
| sys | General Swap File |
| syx | MIDI System Exclusive Message |
| syz | SYSTAT Data |
| sy_ | Compressed SYS File |
| sz | WinAMP Skin |
| sz4 | E-triloquist Phrase Library |
| szs | Wii Game Data |
| szx | Spectaculator ZX-State Snapshot |
| t$m | AVG Internet Security Temporary File |