Data Packs are Satellaview 8M Memory Packs which have data meant to be used as expansion for a Data Pack-compatible game.
Data Pack-compatible game cartridges have a resemblence to the BS-X Cartridge itself. The games which were compatible with Data Packs are:
- Same Game
- Derby Stallion 96
- RPG Tsukuru 2
- Sound Novel Tsukuru
- Ongaku Tsukuru Kanaderu
- Joushou Mahjong Tenpai
- SD Gundam G-NEXT
- Shigesato Itoi no Bass Tsuri No. 1
For most of these games, Data was distributed via St.GIGA's Satellaview services. Same Game and SD Gundam G-Next had some Data Packs sold as retail in stores. RPG Tsukuru 2, Sound Novel Tsukuru and Ongaku Tsukuru Kanaderu could save user-created data to 8M Memory Packs.
RPG Tsukuru 2, Sound Novel Tsukuru and Ongaku Tsukuru Kanaderu apparently have some sort of cross-compatibility with the various data.
On real hardware, there is a way to corrupt a 8M Memory Pack in RPG Tsukuru 2, causing an otherwise rarely seen 'Error 41" message to appear on the BS-X.
The process is detailed in This Youtube Video