Bendix G-15
Encyclopedia
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 (1.5m by 1m by 1m) and weighed about 950 lb
(450 kg). The base system, without peripherals, cost $49,500. A working model cost around $60,000. It could also be rented for $1,485 per month. It was meant for scientific and industrial markets. The series was gradually discontinued when Control Data Corporation
took over the Bendix computer division in 1963.
The chief designer of the G-15 was Harry Huskey
, who had worked with Alan Turing
on the ACE
in the United Kingdom
and on the SWAC
in the 1950s. He made most of the design while working as a professor at Berkeley
, and other universities. David C. Evans
was one of the Bendix engineers on the G-15 project. He would later become famous for his work in computer graphics and for starting up Evans & Sutherland
with Ivan Sutherland
.
, one of several inspired by the ACE
. It used a magnetic drum
to simulate the recirculating delay line
memory of other serial designs. Each track had a set of read and write heads; as soon as a bit was read off a track, it was re-written on the same track a certain distance away. The length of delay, and thus the number of words on a track, was determined by the spacing of the read and write heads, the delay corresponding to the time required for a section of the drum to travel from the write head to the corresponding read head. Under normal operation, data were written back without change, but this data flow could be intercepted at any time, allowing the machine to update sections of a track as needed.
This arrangement allowed the designers to create "delay lines" of any desired length. In addition to the twenty "long lines" of 108 words each, there were four more short lines of four words each. These short lines recycled at 27 times the rate of the long lines, allowing fast access to frequently needed data. Even the machine's accumulators
were implemented as drum lines: three double-word lines used for intermediate storage and double-precision addition, multiplication, and division in addition to a one single-word accumulator. This use of the drum rather than flip-flops for the registers helped to reduce tube count.
A consequence of this design was that, unlike other computers with magnetic drums, the G-15 did not retain its memory when it was shut off. The only permanent tracks were two timing tracks recorded on the drum at the factory. The second track was a backup, as the tracks were liable to erasure if one of their amplifier tubes shorted.
The serial nature of the G-15's memory was carried over into the design of its arithmetic and control circuits. The adders worked on one binary digit at a time, and even the instruction word was designed to minimize the number of bits in an instruction that needed to be retained in flip-flops (to the extent of leveraging another one-word drum line used exclusively for generating address timing signals).
The G-15 had 180 vacuum tube
packs and 300 germanium diode
s. It had a total of about 450 tubes (mostly dual triodes).
Its magnetic drum memory
held 2,160 words of twenty-nine bit
s. Average memory access time was 14.5 milliseconds, but its instruction addressing architecture could reduce this dramatically for well-written programs. Its addition time was 270 microseconds (not counting memory access time). Single-precision multiplication took 2,439 microseconds and double-precision multiplication took 16,700 microseconds.
characters u-z) and about three characters per second for alphabetical characters. The machine's limited storage precluded much output of anything but numbers; occasionally, paper forms with pre-printed fields or labels were inserted into the typewriter. A faster typewriter unit was also available.
The high-speed photoelectric paper tape reader (250 hexadecimal digits per second on five-channel paper tape for the PR-1; 400 characters from 5-8 channel tape for the PR-2) read programs (and occasionally saved data) from tapes that were often mounted in cartridges for easy loading and unloading. Not unlike magnetic tape, the paper tape data were blocked into runs of 108 words or less since that was the maximum read size. A cartridge could contain many multiple blocks, up to 2500 words (~10 kilobyte
s).
While the G-15 had an optional high-speed paper tape punch (the PTP-1 at 60 digits per second) for output, the standard punch operated at 17 hex characters per second (510 byte
s per minute).
Optionally, the AN-1 "Universal Code Accessory" included the "35-4" Friden Flexowriter
and HSR-8 paper tape reader and HSP-8 paper tape punch. The mechanical reader and punch could process paper tapes up to eight channels wide at 110 characters per second.
The CA-1 "Punched Card Coupler" could connect one or two IBM 026 card punches (which were more often used as manual devices) to read cards at 17 columns per second (ca. 12 full cards per minute) or punch cards at 11 columns per second (ca. eight full cards per minute). Partially-full cards were processed more quickly with an 80 column per second skip speed). The more expensive CA-2 Punched Card Coupler read and punched cards at a 100 card per minute rate.
The PA-3 pen plotter ran at one inch per second with 200 increments per inch on a paper roll one foot wide by 100 feet long. The optional retractable penholder eliminated "retrace lines".
The MTA-2 could interface up to four drives for half-inch Mylar magnetic tapes, which could store as many as 300,000 words (in blocks no longer than 108 words). The read/write rate was 430 hexadecimal digits per second; the bidirectional search speed was 2500 characters per second.
The DA-1 differential analyzer facilitated solution of differential equations. It contained 108 integrators and 108 constant multipliers, sporting 34 updates per second.
A symbolic assembler, similar to the IBM 650
's SOAP (Symbolic Optimal Assembly Program), was introduced in the late 1950s and included routines for minimum-access coding. Other programming aids included a supervisor program, Intercom, a floating-point interpretive system, and ALGO
, an algebraic language designed from the 1958 Preliminary Report
of the ALGOL
committee. Users also developed their own tools, and a variant of Intercom suited to the needs of civil engineers is said to have circulated.
Floating point was implemented in software. The "Intercom" series of languages provided an easier to program virtual machine that operated in floating point. Instructions to Intercom 500, 550, and 1000 were numerical, six or seven digits in length. Instructions were stored sequentially; the beauty was convenience, not speed. Intercom 1000 even had an optional double-precision version.
, because it had the Intercom interpretive system. The title is disputed by other machines, such as the LINC
and the PDP-8
, and some maintain that only microcomputers, such as those which appeared in the 1970s, can be called personal computers. Nevertheless, the machine's low acquisition and operating costs, and the fact that it did not require a dedicated operator, meant that organizations could allow users complete access to the machine.
Over 400 G-15s were manufactured. About 300 G-15s were installed in the United States
and a few were sold in other countries such as Australia
and Canada
. The machine found a niche in civil engineering
, where it was used to solve cut and fill
problems. Some have survived and have made their way to computer museums or science and technology museums around the world.
Huskey received one of the last production G15s, fitted with a gold-plated front panel.
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
was introduced in 1956 by the Bendix Corporation
Bendix Corporation
The Bendix Corporation was an American manufacturing and engineering company which during various times in its 60 year existence made brake systems, aeronautical hydraulics, avionics, aircraft and automobile fuel control systems, radios, televisions and computers, and which licensed its name for...
, Computer Division, Los Angeles, California
Los Angeles, California
Los Angeles , with a population at the 2010 United States Census of 3,792,621, is the most populous city in California, USA and the second most populous in the United States, after New York City. It has an area of , and is located in Southern California...
. It was about 5 by 3 by 3 ft (1.5m by 1m by 1m) and weighed about 950 lb
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
(450 kg). The base system, without peripherals, cost $49,500. A working model cost around $60,000. It could also be rented for $1,485 per month. It was meant for scientific and industrial markets. The series was gradually discontinued when Control Data Corporation
Control Data Corporation
Control Data Corporation was a supercomputer firm. For most of the 1960s, it built the fastest computers in the world by far, only losing that crown in the 1970s after Seymour Cray left the company to found Cray Research, Inc....
took over the Bendix computer division in 1963.
The chief designer of the G-15 was Harry Huskey
Harry Huskey
Harry Douglas Huskey is an American computer designer pioneer.Huskey was born in the Smoky Mountains region of North Carolina and grew up in Idaho. He gained his Master's and then his PhD in 1943 from the Ohio State University on Contributions to the Problem of Geocze...
, who had worked with Alan Turing
Alan Turing
Alan Mathison Turing, OBE, FRS , was an English mathematician, logician, cryptanalyst, and computer scientist. He was highly influential in the development of computer science, providing a formalisation of the concepts of "algorithm" and "computation" with the Turing machine, which played a...
on 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...
in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and on the SWAC
SWAC (computer)
The SWAC was an early electronic digital computer built in 1950 by the U.S. National Bureau of Standards in Los Angeles, California. It was designed by Harry Huskey...
in the 1950s. He made most of the design while working as a professor at Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
, and other universities. David C. Evans
David C. Evans
David Cannon Evans was the founder of the computer science department at the University of Utah and co-founder of Evans & Sutherland, a computer firm which is known as a pioneer in the domain of computer-generated imagery.-Biography:Evans attended the University of Utah and studied electrical...
was one of the Bendix engineers on the G-15 project. He would later become famous for his work in computer graphics and for starting up Evans & Sutherland
Evans & Sutherland
Evans & Sutherland is a computer firm involved in the computer graphics field. Their products are used primarily by the military and large industrial firms for training and simulation, and in digital projection environments like planetariums.-History:...
with Ivan Sutherland
Ivan Sutherland
Ivan Edward Sutherland is an American computer scientist and Internet pioneer. He received the Turing Award from the Association for Computing Machinery in 1988 for the invention of Sketchpad, an early predecessor to the sort of graphical user interface that has become ubiquitous in personal...
.
Architecture
The G-15 was a serial-architecture machineSerial computer
A serial computer is typified by internally operating on one bit or digit for each clock cycle. Machines with serial main storage devices such as acoustic or magnetostrictive delay lines and rotating magnetic devices were usually serial computers....
, one of several inspired by 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...
. It used a magnetic drum
Drum memory
Drum memory is a magnetic data storage device and was an early form of computer memory widely used in the 1950s and into the 1960s, invented by Gustav Tauschek in 1932 in Austria....
to simulate the recirculating delay line
Delay line
Delay line may refer to:* Propagation delay, the length of time taken for something to reach its destination* Analog delay line, used to delay a signal...
memory of other serial designs. Each track had a set of read and write heads; as soon as a bit was read off a track, it was re-written on the same track a certain distance away. The length of delay, and thus the number of words on a track, was determined by the spacing of the read and write heads, the delay corresponding to the time required for a section of the drum to travel from the write head to the corresponding read head. Under normal operation, data were written back without change, but this data flow could be intercepted at any time, allowing the machine to update sections of a track as needed.
This arrangement allowed the designers to create "delay lines" of any desired length. In addition to the twenty "long lines" of 108 words each, there were four more short lines of four words each. These short lines recycled at 27 times the rate of the long lines, allowing fast access to frequently needed data. Even the machine's accumulators
Processor register
In computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are addressed by mechanisms other than main memory and can be accessed more quickly...
were implemented as drum lines: three double-word lines used for intermediate storage and double-precision addition, multiplication, and division in addition to a one single-word accumulator. This use of the drum rather than flip-flops for the registers helped to reduce tube count.
A consequence of this design was that, unlike other computers with magnetic drums, the G-15 did not retain its memory when it was shut off. The only permanent tracks were two timing tracks recorded on the drum at the factory. The second track was a backup, as the tracks were liable to erasure if one of their amplifier tubes shorted.
The serial nature of the G-15's memory was carried over into the design of its arithmetic and control circuits. The adders worked on one binary digit at a time, and even the instruction word was designed to minimize the number of bits in an instruction that needed to be retained in flip-flops (to the extent of leveraging another one-word drum line used exclusively for generating address timing signals).
The G-15 had 180 vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
packs and 300 germanium diode
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
s. It had a total of about 450 tubes (mostly dual triodes).
Its magnetic drum memory
Drum memory
Drum memory is a magnetic data storage device and was an early form of computer memory widely used in the 1950s and into the 1960s, invented by Gustav Tauschek in 1932 in Austria....
held 2,160 words of twenty-nine bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
s. Average memory access time was 14.5 milliseconds, but its instruction addressing architecture could reduce this dramatically for well-written programs. Its addition time was 270 microseconds (not counting memory access time). Single-precision multiplication took 2,439 microseconds and double-precision multiplication took 16,700 microseconds.
Peripherals
One of the G-15's primary output devices was the typewriter with an output speed of about 10 characters per second for numbers (and lower-case hexadecimalHexadecimal
In mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...
characters u-z) and about three characters per second for alphabetical characters. The machine's limited storage precluded much output of anything but numbers; occasionally, paper forms with pre-printed fields or labels were inserted into the typewriter. A faster typewriter unit was also available.
The high-speed photoelectric paper tape reader (250 hexadecimal digits per second on five-channel paper tape for the PR-1; 400 characters from 5-8 channel tape for the PR-2) read programs (and occasionally saved data) from tapes that were often mounted in cartridges for easy loading and unloading. Not unlike magnetic tape, the paper tape data were blocked into runs of 108 words or less since that was the maximum read size. A cartridge could contain many multiple blocks, up to 2500 words (~10 kilobyte
Kilobyte
The kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
s).
While the G-15 had an optional high-speed paper tape punch (the PTP-1 at 60 digits per second) for output, the standard punch operated at 17 hex characters per second (510 byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
s per minute).
Optionally, the AN-1 "Universal Code Accessory" included the "35-4" Friden Flexowriter
Friden Flexowriter
The Friden Flexowriter was a teleprinter, a heavy duty electric typewriter capable of being driven not only by a human typing, but also automatically by several methods including direct attachment to a computer and by use of paper tape....
and HSR-8 paper tape reader and HSP-8 paper tape punch. The mechanical reader and punch could process paper tapes up to eight channels wide at 110 characters per second.
The CA-1 "Punched Card Coupler" could connect one or two IBM 026 card punches (which were more often used as manual devices) to read cards at 17 columns per second (ca. 12 full cards per minute) or punch cards at 11 columns per second (ca. eight full cards per minute). Partially-full cards were processed more quickly with an 80 column per second skip speed). The more expensive CA-2 Punched Card Coupler read and punched cards at a 100 card per minute rate.
The PA-3 pen plotter ran at one inch per second with 200 increments per inch on a paper roll one foot wide by 100 feet long. The optional retractable penholder eliminated "retrace lines".
The MTA-2 could interface up to four drives for half-inch Mylar magnetic tapes, which could store as many as 300,000 words (in blocks no longer than 108 words). The read/write rate was 430 hexadecimal digits per second; the bidirectional search speed was 2500 characters per second.
The DA-1 differential analyzer facilitated solution of differential equations. It contained 108 integrators and 108 constant multipliers, sporting 34 updates per second.
Software
A problem peculiar to machines with serial memory is the latency of the storage medium: Instructions and data are not always immediately available and, in the worst case, one must wait for the complete recirculation of a delay line to obtain data from a given memory address. The problem was addressed in the G-15 by what the Bendix literature called "minimum-access coding." Each instruction carried with it the address of the next instruction to be executed, allowing the programmer to arrange instructions such that when one instruction completed, the next instruction was about to appear under the read head for its line. Data could be staggered in a similar manner. To aid this process, the coding sheets included a table containing numbers of all addresses; the programmer would cross off each address as it was used.A symbolic assembler, similar to 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...
's SOAP (Symbolic Optimal Assembly Program), was introduced in the late 1950s and included routines for minimum-access coding. Other programming aids included a supervisor program, Intercom, a floating-point interpretive system, and ALGO
ALGO
ALGO is an algebraic programming language developed between 1959 and 1961 for the Bendix G-15 computer.ALGO was one of several programming languages inspired by the Preliminary Report on the International Algorithmic Language written in Zürich in 1958. This report underwent several modifications...
, an algebraic language designed from the 1958 Preliminary Report
ALGOL 58
ALGOL 58, originally known as IAL, is one of the family of ALGOL computer programming languages. It was an early compromise design soon superseded by ALGOL 60...
of the ALGOL
ALGOL
ALGOL is a family of imperative computer programming languages originally developed in the mid 1950s which greatly influenced many other languages and became the de facto way algorithms were described in textbooks and academic works for almost the next 30 years...
committee. Users also developed their own tools, and a variant of Intercom suited to the needs of civil engineers is said to have circulated.
Floating point was implemented in software. The "Intercom" series of languages provided an easier to program virtual machine that operated in floating point. Instructions to Intercom 500, 550, and 1000 were numerical, six or seven digits in length. Instructions were stored sequentially; the beauty was convenience, not speed. Intercom 1000 even had an optional double-precision version.
Significance
The G-15 is sometimes described as the first personal computerPersonal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
, because it had the Intercom interpretive system. The title is disputed by other machines, such as the LINC
LINC
The LINC was a 12-bit, 2048-word computer. The LINC can be considered the first minicomputer and a forerunner to the personal computer....
and the PDP-8
PDP-8
The 12-bit PDP-8 was the first successful commercial minicomputer, produced by Digital Equipment Corporation in the 1960s. DEC introduced it on 22 March 1965, and sold more than 50,000 systems, the most of any computer up to that date. It was the first widely sold computer in the DEC PDP series of...
, and some maintain that only microcomputers, such as those which appeared in the 1970s, can be called personal computers. Nevertheless, the machine's low acquisition and operating costs, and the fact that it did not require a dedicated operator, meant that organizations could allow users complete access to the machine.
Over 400 G-15s were manufactured. About 300 G-15s were installed in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and a few were sold in other countries such as Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. The machine found a niche in civil engineering
Civil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings...
, where it was used to solve cut and fill
Cut and fill
In earthmoving, cut and fill is the process of constructing a railway, road or canal whereby the amount of material from cuts roughly matches the amount of fill needed to make nearby embankments, so minimizing the amount of construction labor...
problems. Some have survived and have made their way to computer museums or science and technology museums around the world.
Huskey received one of the last production G15s, fitted with a gold-plated front panel.
