Optimum programming
Encyclopedia
In the history of computing, optimum programming is the practice of arranging a computer program's instructions in memory so as to minimize the time the machine spends waiting for instructions. It is of historical interest mainly due to the design of many early digital computers.
Most early computers used some form of serial memory (primarily delay line memory
). Unlike the random access memory of modern computers, words in serial memory are made available one at a time; the time required to access a particular word depends on the "distance" between it and the word currently being read. If a given line held n words, the average time to read a word would be
word times. Without optimum coding, such a machine would spend most of its time idly waiting for instructions and data.
To circumvent this problem, many machines, particularly the ACE
and its descendants, included in their instruction format a field specifying the address of the next instruction to be executed. Employing optimum coding, the programmer could locate an instruction such that it would be available in memory just as the preceding instruction had finished. For example, if a programmer had just coded an ADD instruction at address 400, and the ADD instruction required 4 word-times to execute, the programmer would set the "Next Address" field of the instruction to 404, and would place the next instruction there.
In the United States, optimum coding was most commonly employed on the IBM 650
and the Bendix G-15
. Both machines had optimizing assemblers (SOAP for the IBM, POGO for Bendix) that could automate this task.
Most early computers used some form of serial memory (primarily delay line memory
Delay line memory
Delay line memory was a form of computer memory used on some of the earliest digital computers. Like many modern forms of electronic computer memory, delay line memory was a refreshable memory, but as opposed to modern random-access memory, delay line memory was serial-access...
). Unlike the random access memory of modern computers, words in serial memory are made available one at a time; the time required to access a particular word depends on the "distance" between it and the word currently being read. If a given line held n words, the average time to read a word would be
word times. Without optimum coding, such a machine would spend most of its time idly waiting for instructions and data.To circumvent this problem, many machines, particularly the ACE
ACE (computer)
The Automatic Computing Engine was an early electronic stored-program computer design produced by Alan Turing at the invitation of John R. Womersley, superintendent of the Mathematics Division of the National Physical Laboratory . The use of the word Engine was in homage to Charles Babbage and his...
and its descendants, included in their instruction format a field specifying the address of the next instruction to be executed. Employing optimum coding, the programmer could locate an instruction such that it would be available in memory just as the preceding instruction had finished. For example, if a programmer had just coded an ADD instruction at address 400, and the ADD instruction required 4 word-times to execute, the programmer would set the "Next Address" field of the instruction to 404, and would place the next instruction there.
In the United States, optimum coding was most commonly employed on the IBM 650
IBM 650
The IBM 650 was one of IBM’s early computers, and the world’s first mass-produced computer. It was announced in 1953, and over 2000 systems were produced between the first shipment in 1954 and its final manufacture in 1962...
and the Bendix G-15
Bendix G-15
The Bendix G-15 computer was introduced in 1956 by the Bendix Corporation, Computer Division, Los Angeles, California. It was about 5 by 3 by 3 ft and weighed about 950 lb . The base system, without peripherals, cost $49,500. A working model cost around $60,000. It could also be rented for...
. Both machines had optimizing assemblers (SOAP for the IBM, POGO for Bendix) that could automate this task.
See also
- Mel KayeMel KayeThe Story of Mel is an archetypical piece of computer programming folklore. Its subject, Mel Kaye, is the canonical Real Programmer.- Story :Ed Nather’s The Story of Mel details the extraordinary programming prowess of a former collegue of his, "Mel", at Royal McBee Computer Corporation...
, who authored one particularity clever bit of optimum programming that has entered computer lore.