bookshelf, archives
档 centers on organized storage of written records: a bookshelf or archive where documents are kept in order.
档 combines 木 (wood) with 当, which likely contributes the sound. The wood radical suggests a wooden shelf or cabinet for storing books and records.
A wooden 木 shelf 当 holds rows of books and archived documents: 档 is a bookshelf or archive.
For トウ, imagine a tall wooden bookshelf shaped like the number 10 (とう, ten): 10 -> トウ, and the shelf stores archives.
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