The Harvard architecture is a computer architecture with separate storage and signal pathways for instructions and data. It contrasts with the von Neumann architecture, where program instructions and data share the same memory and pathways.

The term originated from the Harvard Mark I relay-based computer, which stored instructions on punched tape (24 bits wide) and data in electro-mechanical counters (although both the origin, and the meaning commonly given the term 'Harvard architecture', has been challenged in 'The Myth of the Harvard Architecture' published by the IEEE Annals of the History of Computing). These early machines had data storage entirely contained within the central processing unit, and provided no access to the instruction storage as data. Programs needed to be loaded by an operator; the processor could not initialize itself.

Modern processors appear to the user to be systems with von Neumann architectures, with the program code stored in the same main memory as the data. For performance reasons, internally and largely invisible to the user, most designs have separate processor caches for the instructions and data, with separate pathways into the processor for each. This is one form of what is known as the modified Harvard architecture.

Harvard architecture is historically, and traditionally, split into two address spaces, but having three, i.e. two extra (and all accessed in each cycle) is also done, while rare.