Abstract: The Sequential Codelet Model is a definition of a program execution model that aims to achieve parallel execution of programs that are expressed sequentially and in a hierarchical manner. The Sequential Codelet Model heavily borrows from the successful experience acquired through decades of sequential program execution, in particular, the use of Instruction Level Parallelism optimizations for implicit parallel execution of code. We revisit and re-define the Universal Turing Machine and the Von Neumann Architecture to account for the hierarchical organization of the whole computation system and its resources (i.e. memory, computational capabilities, and interconnection networks), as well as consider program complexity and structure in relation to its execution. This work defines the Sequential Codelet Model (SCM), the Hierarchical Turing Machine (HTM), and the Hierarchal Von Neumann Architecture, as well as explains how implicit parallel execution of programs could be achieved by using these definitions.