Shelf guide · 18 June 2026
Programs, kept on a separate shelf
A program is the part of Solana that changes account data. We keep it on its own shelf so it is not mistaken for a transaction or for a person.
After accounts and transactions, the word program is the one that makes visitors go quiet. They have heard it used for phone software, for a workshop timetable, and for a television listing. On Solana it has a narrower job, and the library gives it a shelf of its own so the other meanings can stay outside.
Code that lives in an account
A program is stored on the network in an account marked executable. That is the whole housing. There is no separate cupboard. The same account idea from the first shelf now holds compiled code instead of an empty data field. Once you accept that, a program id stops being a mystical string and becomes an address you could, in principle, write on a card: this address, executable, owned by the loader that deployed it.
An instruction is not a program. An instruction is one request sent to a program, naming the accounts it may touch and the action to perform. The study series spends an evening on that distinction because mixing the two words makes every later paragraph wobble. People leave evening five able to say: the program is the code at this address; the instruction is the request I handed it.
The owner rule
Data accounts have an owner field, and that owner is a program. The working rule we repeat is strict: the bytes in an account are rewritten by its owner program. Another program may be allowed to read, and a transaction may include both, but the lock on the data belongs to the owner. This is why the owner line on the account card is not decoration. If you misread the owner, you will ask the wrong program to perform the change, and the transaction will fail closed.
Two programs are enough for a first shelf. The system program creates ordinary accounts and moves SOL. The SPL token program, which learners meet by that name only, is the later shelf for token accounts. We do not pretend the token shelf is part of the first six evenings. Naming it early, and then leaving it closed, keeps visitors from dragging every question back to tokens.
What the first series will not do
Nobody deploys a program in the Fundamentals Study Series. Deployment needs a compiler, a build, and a funded account, and it pulls attention away from reading. We name deployment so the word is familiar, then we send curious learners to a desk hour months later if they still want it. The public series ends when you can explain the owner rule with a pencil. That is a smaller promise than a software course, and it is the one Han is willing to keep.