description: Viewing and Modifying SAS Formats in Data Controller
---
# Formats
SAS Formats are stored in Catalogs, and are used for in-memory lookup operations. Some formats are available by default, others (custom formats) are maintained seperately.
Viewing or editing a format catalog will always mean that the entire catalog is exported, before being filtered (if filters applied) and displayed. For this reason, it is recommended to split a large format catalog over several catalogs, if performance is a consideration.
When adding a format to MPE_TABLES, the `DSN` should contain the format catalog name plus a `-FC` extension. The LOADTYPE should be `FORMAT_CAT` and the BUSKEY should be `FMTNAME START`. HOOK scripts can also be applied (run some DQ after an edit, or re-run a batch job after an approval).