| yaml | YAML Document |
| ycf | FKR Program YCF Data |
| ychat | Yahoo! Messenger Chat Log |
| yg0 | Corel Paradox Secondary Index |
| yg1 | Corel Paradox Secondary Index |
| yg2 | Corel Paradox Secondary Index |
| yls | YuleLog Data |
| ymg | Yahoo! Messenger Data |
| yml | YAML Document |
| ymt | Yar Material File |
| ypf | YahElite Personality File |
| yrcbck | YRC Weblink Backup Archive |
| yrcbkm | YRC Weblink Bookmarks Archive |
| yrcdat | YRC Weblink Data Script |
| ytf | YTGen Population Data |
| ytm | YTGen Method Data |
| ytr | IRIS OCR Data |
| yyc | Wave Sapphire Distribution File |
| z1 | Z-machine Z-code File |
| z2 | Z-machine Z-code File |
| z3 | Z-machine Z-code File |
| z3l | ZW3D Part Library |
| z4 | Z-machine Z-code File |
| z5 | Z-machine Z-code File |
| z6 | Z-machine Z-code File |
| z64 | N64 ROM Image Mr. Backup Z64 |
| z7 | Z-machine Z-code File |
| z8 | Z-machine Z-code File |
| z80 | ZX Spectrum Emulator Snapshot Z80 |
| zak | Carlson Survey Coordinate Data |
