···11-Picking up from day 2: [records](https://atproto.com/guides/glossary#record) are kept in [repo](https://atproto.com/guides/glossary#data-repo)s on the
22-[PDS](https://atproto.com/guides/glossary#pds-personal-data-server), and today we're looking at the repo!
11+To recap: [records](https://atproto.com/guides/glossary#record) are kept in [repo](https://atproto.com/guides/glossary#data-repo)s on [PDS](https://atproto.com/guides/glossary#pds-personal-data-server)es.
22+33+**Today we're looking at the repo!** Or at least its serialized format.
44+55+The repo (repository) is a key-value store of repo-keys to records. The data structure used is called a Merkle Search Tree (MST), but we're not going to worry about that just yet.
66+77+Wait, "repo keys"?? Remember [yesterday](./2) how an at-uri is made of three parts, `at://<did>/<collection>/<rkey>`? The second two parts together, `<collection>/<rkey>`, make up the actual raw keys (repo keys) inside your atproto repository.
88+3944-The repo (repository) is a key-value store
510611TODO blah blah merkle tree but not getting too distracted because this is about the CAR
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