Stored-program computer
Encyclopedia
A stored-program computer is one which stores program instructions in electronic memory. Often the definition is extended with the requirement that the treatment of programs and data in memory be interchangeable or uniform.
A computer with a von Neumann architecture
stores program data and instruction data in the same memory; a computer with a Harvard architecture
has separate memories for storing program and data.
Stored-program computer is sometimes used as a synonym for von Neumann architecture, however Professor Jack Copeland
considers that it is "historically inappropriate, to refer to electronic stored-program digital computers as 'von Neumann machines'". Hennessy and Patterson write that the early Harvard machines were regarded as "reactionary by the advocates of stored-program computers".
The stored-program computer idea can be traced back to the 1936 theoretical concept of a universal Turing machine
. Von Neumann was aware of this paper, and he impressed it on his collaborators as well.
Many early computers, such as the Atanasoff–Berry Computer, were not reprogrammable. They executed a single hardwired program. As there were no program instructions, no program storage was necessary. Other computers, though programmable, stored their programs on punched tape
which was physically fed into the machine as needed.
The University of Manchester
's Small-Scale Experimental Machine
(SSEM) is generally recognized as world's first electronic computer that ran a stored program—an event that occurred on June 21, 1948. However the SSEM was not regarded as full-fledged computer, more a proof of concept
that was built on to produce the Manchester Mark 1
computer. On May 6, 1949 the EDSAC
in Cambridge ran its first program, and due to this event, it is considered "the first complete and fully operational regular electronic digital stored-program computer". It is sometimes claimed that the IBM SSEC, operational in January 1948, was the first stored-program computer; this claim is controversial, not least because of the hierarchical memory system of the SSEC, and because some aspects of its operations, like access to relays or tape drives, were determined by plugging.
A computer with a von Neumann architecture
Von Neumann architecture
The term Von Neumann architecture, aka the Von Neumann model, derives from a computer architecture proposal by the mathematician and early computer scientist John von Neumann and others, dated June 30, 1945, entitled First Draft of a Report on the EDVAC...
stores program data and instruction data in the same memory; a computer with a Harvard architecture
Harvard architecture
The Harvard architecture is a computer architecture with physically separate storage and signal pathways for instructions and data. The term originated from the Harvard Mark I relay-based computer, which stored instructions on punched tape and data in electro-mechanical counters...
has separate memories for storing program and data.
Stored-program computer is sometimes used as a synonym for von Neumann architecture, however Professor Jack Copeland
Jack Copeland
Brian Jack Copeland is Professor of Philosophy at the University of Canterbury, Christchurch, New Zealand.Copeland received a BPhil and DPhil from the University of Oxford in philosophy, where he undertook research on modal and non-classical logic.He is the Director of the Turing Archive for the...
considers that it is "historically inappropriate, to refer to electronic stored-program digital computers as 'von Neumann machines'". Hennessy and Patterson write that the early Harvard machines were regarded as "reactionary by the advocates of stored-program computers".
The stored-program computer idea can be traced back to the 1936 theoretical concept of a universal Turing machine
Universal Turing machine
In computer science, a universal Turing machine is a Turing machine that can simulate an arbitrary Turing machine on arbitrary input. The universal machine essentially achieves this by reading both the description of the machine to be simulated as well as the input thereof from its own tape. Alan...
. Von Neumann was aware of this paper, and he impressed it on his collaborators as well.
Many early computers, such as the Atanasoff–Berry Computer, were not reprogrammable. They executed a single hardwired program. As there were no program instructions, no program storage was necessary. Other computers, though programmable, stored their programs on punched tape
Punched tape
Punched tape or paper tape is an obsolete form of data storage, consisting of a long strip of paper in which holes are punched to store data...
which was physically fed into the machine as needed.
The University of Manchester
University of Manchester
The University of Manchester is a public research university located in Manchester, United Kingdom. It is a "red brick" university and a member of the Russell Group of research-intensive British universities and the N8 Group...
's Small-Scale Experimental Machine
Small-Scale Experimental Machine
The Manchester Small-Scale Experimental Machine , nicknamed Baby, was the world's first stored-program computer. It was built at the Victoria University of Manchester by Frederic C...
(SSEM) is generally recognized as world's first electronic computer that ran a stored program—an event that occurred on June 21, 1948. However the SSEM was not regarded as full-fledged computer, more a proof of concept
Proof of concept
A proof of concept or a proof of principle is a realization of a certain method or idea to demonstrate its feasibility, or a demonstration in principle, whose purpose is to verify that some concept or theory that has the potential of being used...
that was built on to produce the Manchester Mark 1
Manchester Mark 1
The Manchester Mark 1 was one of the earliest stored-program computers, developed at the Victoria University of Manchester from the Small-Scale Experimental Machine or "Baby" . It was also called the Manchester Automatic Digital Machine, or MADM...
computer. On May 6, 1949 the EDSAC
EDSAC
Electronic Delay Storage Automatic Calculator was an early British computer. The machine, having been inspired by John von Neumann's seminal First Draft of a Report on the EDVAC, was constructed by Maurice Wilkes and his team at the University of Cambridge Mathematical Laboratory in England...
in Cambridge ran its first program, and due to this event, it is considered "the first complete and fully operational regular electronic digital stored-program computer". It is sometimes claimed that the IBM SSEC, operational in January 1948, was the first stored-program computer; this claim is controversial, not least because of the hierarchical memory system of the SSEC, and because some aspects of its operations, like access to relays or tape drives, were determined by plugging.