Program code is decoded and interpreted as instruction to control the combinatorial and sequential logic while executing a program within its processor, usually distinct from application specific data, if the application is not an assembler, compiler or debugger or anything related to self-modifying code or self-replication. It fits into one processor register and is subject of arithmetical or logical operations, or, if interpreted as (part of an) address, to perform random memory access, that is to store and retrieve primitive data items. One of these data items may represent numbers in various formats and value ranges, finite sets, codes like a character of a text or a piece on the chessboard, or even instruction codes and memory addresses.
From processor's point of view, an atomic fixed sized data item with a unique memory address is a primitive data item, today usually with a size of one, two, four, or up to eight bytes, sometimes even 16 or 32 bytes.
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