| x_n | Parasolid CAD ASCII Drawing Data |
| x_t | Parasolid CAD ASCII Parts Data |
| y01 | Corel Paradox Secondary Index |
| y02 | Corel Paradox Secondary Index |
| y03 | Corel Paradox Secondary Index |
| y04 | Corel Paradox Secondary Index |
| y05 | Corel Paradox Secondary Index |
| y06 | Corel Paradox Secondary Index |
| y07 | Corel Paradox Secondary Index |
| y08 | Corel Paradox Secondary Index |
| y09 | Corel Paradox Secondary Index |
| yah | HeartBeat Data |
| yam | Yahoo! Auctions Data |
| yam | YAML Document |
| yaml | YAML Document |
| yap | Castles and Catapults Game Data |
| yar | Raynen-Qili KnitCAD Yarn Carrier Data |
| yarn | Yarn Data |
| yast | YaST Data |
| ybm | Ad-Aware 2007 Data |
| ycd | Y-Cruncher Data |
| ycf | FKR Program YCF Data |
| ychat | Yahoo! Messenger Chat Log |
| ycr | YHC Core |
| yct | YahELite Chat Transcript Data |
| ydsp | eXtendable Wad Editor YDSP Data |
| yef | Yoda Export Data |
| yg0 | Corel Paradox Secondary Index |
| yg1 | Corel Paradox Secondary Index |
| yg2 | Corel Paradox Secondary Index |