LGP-30
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The LGP-30, standing for Librascope General Purpose and then Librascope General Precision, is an early off-the-shelf computer. It was manufactured by the Librascope company of
Glendale, California Glendale is a city located primarily in the Verdugo Mountains region, with a small portion in the San Fernando Valley, of Los Angeles County, California, United States. It is located about north of downtown Los Angeles. As of 2024, Glendale ha ...
(a division of General Precision Inc.), and sold and serviced by the Royal Precision Electronic Computer Company, a joint venture with the Royal McBee division of the Royal Typewriter Company. The LGP-30 was first manufactured in 1956, at a retail price of $47,000, . The LGP-30 was commonly referred to as a desk computer. Its height, width, and depth, excluding the typewriter shelf, was . It weighed about , and was mounted on sturdy casters which facilitated moving the unit.


Design

The primary design consultant for the Librascope computer was Stan Frankel, a
Manhattan Project The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada. From 1942 to 1946, the ...
veteran and one of the first programmers of
ENIAC ENIAC (; Electronic Numerical Integrator and Computer) was the first Computer programming, programmable, Electronics, electronic, general-purpose digital computer, completed in 1945. Other computers had some of these features, but ENIAC was ...
, assisted by James Cass, at the time a graduate student at
Caltech The California Institute of Technology (branded as Caltech) is a private university, private research university in Pasadena, California, United States. The university is responsible for many modern scientific advancements and is among a small g ...
. They designed a usable computer with a minimal amount of hardware. The single address
instruction set In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, s ...
had only 16 commands. Magnetic
drum memory Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria. Drums were widely used in the 1950s and into the 1960s as computer memory. Many early computers, called drum computers or drum machines, used drum ...
held the
main memory Computer data storage or digital data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers. The central processin ...
, and the
central processing unit A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary Processor (computing), processor in a given computer. Its electronic circuitry executes Instruction (computing), instructions ...
(CPU)
processor register A processor register is a quickly accessible location available to a computer's processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-onl ...
s, timing information, and the master bit clock, each on a dedicated track. The number of
vacuum tube A vacuum tube, electron tube, thermionic valve (British usage), or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. It ...
s (113) was minimized by using solid-state diode logic, a
bit-serial architecture In computer architecture, bit-serial architectures send data one bit at a time, along a single wire, in contrast to Parallel transmission, bit-parallel word (computer architecture), word architectures, in which data values are sent all bits or a ...
and multiple use of each of the 15 flip-flops. It was a binary, 31-bit word
computer A computer is a machine that can be Computer programming, programmed to automatically Execution (computing), carry out sequences of arithmetic or logical operations (''computation''). Modern digital electronic computers can perform generic set ...
with a 4096-
word A word is a basic element of language that carries semantics, meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of what a word is, there is no consensus among linguist ...
drum memory Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria. Drums were widely used in the 1950s and into the 1960s as computer memory. Many early computers, called drum computers or drum machines, used drum ...
. Standard inputs were the Flexowriter keyboard and paper tape (ten six-bit characters/second). The standard output was the Flexowriter printer (
typewriter A typewriter is a Machine, mechanical or electromechanical machine for typing characters. Typically, a typewriter has an array of Button (control), keys, and each one causes a different single character to be produced on paper by striking an i ...
, working at 10 characters/second). An optional higher-speed paper tape reader and punch was available as a separate peripheral. The computer contained 113 electronic tubes and 1450
diode A diode is a two-Terminal (electronics), terminal electronic component that conducts electric current primarily in One-way traffic, one direction (asymmetric electrical conductance, conductance). It has low (ideally zero) Electrical resistance ...
s. The tubes were mounted on 34 etched circuit pluggable cards which also contain associated components. The 34 cards were of only 12 different types. Card-extenders were available to permit dynamic testing of all machine functions. 680 of the 1450 diodes were mounted on one pluggable logic board. The LGP-30 required 1500
watt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...
s operating under full load. The power inlet cord could plug into any standard 115
volt The volt (symbol: V) is the unit of electric potential, Voltage#Galvani potential vs. electrochemical potential, electric potential difference (voltage), and electromotive force in the International System of Units, International System of Uni ...
60-cycle single-phase line. The computer incorporated
voltage regulation In electrical engineering, particularly power engineering, voltage regulation is a measure of change in the voltage magnitude between the sending and receiving end of a component, such as a transmission line, transmission or distribution line. Vol ...
suitable for powerline variation of 95 to 130 volts. In addition to power regulation, the computer also contained circuitry for a warm-up stage, which minimized thermal shock to the tubes to ensure longer life. The computer contained a cooling fan which directed filtered
air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
through ducts to the tubes and diodes, to extend component life and ensure proper operation. No expensive
air conditioning Air conditioning, often abbreviated as A/C (US) or air con (UK), is the process of removing heat from an enclosed space to achieve a more comfortable interior temperature, and in some cases, also controlling the humidity of internal air. Air c ...
was necessary if the LGP-30 was operated at reasonable temperatures. Al Barr, professor of Computer Science at Caltech, noted in 2023 the power saving features of the design. "Much of the computer hardware before the LGP-30 used far too many vacuum tubes. Vacuum tubes used a great deal of electrical power, produced a lot of heat, and were fairly unreliable since they frequently burned out like incandescent light bulbs. The LGP-30 used a goodly amount of solid-state diode logic to reduce the number of vacuum tubes, increasing its reliability and decreasing its power use. The hardware design was one of the stepping stones that opened the door to the modern computer revolution." There were 32 bit locations per drum word, but only 31 were used, permitting a "restoration of magnetic flux in the head" at the 32nd bit time. Since there was only one address per instruction, a method was needed to optimize allocation of
operand In mathematics, an operand is the object of a mathematical operation, i.e., it is the object or quantity that is operated on. Unknown operands in equalities of expressions can be found by equation solving. Example The following arithmetic expres ...
s. Otherwise, each instruction would wait a complete drum (or disk) revolution each time a data reference was made. The LGP-30 provided for
operand In mathematics, an operand is the object of a mathematical operation, i.e., it is the object or quantity that is operated on. Unknown operands in equalities of expressions can be found by equation solving. Example The following arithmetic expres ...
-location optimization by interleaving the
logical address In computing, a logical address is the address at which an item ( memory cell, storage element, network host) appears to reside from the perspective of an executing application program. A logical address may be different from the physical addr ...
es on the drum so that two adjacent addresses (e.g., 00 and 01) were separated by nine physical locations. These spaces allowed for operands to be located next to the instructions which use them. There were 64 tracks, each with 64 words (sectors). The time between two adjacent physical words was about 0.260
millisecond A millisecond (from '' milli-'' and second; symbol: ms) is a unit of time in the International System of Units equal to one thousandth (0.001 or 10−3 or 1/1000) of a second or 1000 microseconds. A millisecond is to one second, as one second i ...
(ms), and the time between two adjacent addresses was 9 x 0.260 or 2.340 ms. The worst-case access time was 16.66 ms. Half of the instruction (15 bits) was unused. The unused half could have been used for extra instructions, indexing, indirect addressing, or a second (+1) address to locate the next instruction, each of which would have increased program performance. None of these features were implemented in the LGP-30, but some were realized in its 1960 successor, the RPC-4000. A unique feature of the LGP-30 was its built-in multiplication, despite being an inexpensive computer. Since this was a drum computer, bits were processed serially as they were read from the drum. As it did each of the additions associated with the multiplication, it effectively shifted the operand right, acting as if the binary point were on the left side of the word, as opposed to the right side as on most other computers. The divide operation worked similarly. To further reduce costs, the traditional
front panel A front panel was used on early electronic computers to display and allow the alteration of the state of the machine's internal CPU register, registers and computer memory, memory. The front panel usually consisted of arrays of electric light, ...
lights showing internal registers were absent. Instead, Librascope mounted a small
oscilloscope An oscilloscope (formerly known as an oscillograph, informally scope or O-scope) is a type of electronic test instrument that graphically displays varying voltages of one or more signals as a function of time. Their main purpose is capturing i ...
on the front panel that displayed the output from the three register read heads, one above the other, allowing the operator to see and read the bits. Horizontal and vertical size controls let the operator adjust the display to match a plastic overlay engraved with the bit numbers. To read bits the operator counted the up- and down-transitions of the oscilloscope trace. Unlike other computers of its day, internal data was represented in
hexadecimal Hexadecimal (also known as base-16 or simply hex) is a Numeral system#Positional systems in detail, positional numeral system that represents numbers using a radix (base) of sixteen. Unlike the decimal system representing numbers using ten symbo ...
instead of
octal Octal (base 8) is a numeral system with eight as the base. In the decimal system, each place is a power of ten. For example: : \mathbf_ = \mathbf \times 10^1 + \mathbf \times 10^0 In the octal system, each place is a power of eight. For ex ...
, but being a very inexpensive machine it used the physical typewriter keys that correspond to positions 10 to 15 in the type basket for the six non-decimal characters (as opposed to the now normal A – F) to represent those values, resulting in 0 – 9 f g j k q w, which was remembered using the
mnemonic A mnemonic device ( ), memory trick or memory device is any learning technique that aids information retention or retrieval in the human memory, often by associating the information with something that is easier to remember. It makes use of e ...
" Fiber-Glass
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s Kill Quite Well".


Specifications

*Word length: 31 bits, including a sign bit, but no blank spacer bit *Memory size: 4096 words *Speed: 0.260 milliseconds access time between two adjacent physical words; access times between two adjacent addresses 2.340 milliseconds. *Addition time: 0.26 ms excluding access time *Multiplication or division time: 17 ms excluding access time *Clock rate: 120 kHz *Power consumption: 1500
Watt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...
s *Heat dissipation: *Arithmetic element: three working registers: C the counter register, R the instruction register and A the accumulator register. *Instruction format: Sixteen instructions using half-word format *Technology: 113 vacuum tubes and 1350 diodes. *Number produced; 320~493 *First delivery: September 1956 *Price: $47,000 *Successor: LGP-21 *Achievements: The LGP-30 was one of the first desk-sized computers offering small-scale scientific computing. The LGP-30 was fairly popular with "half a thousand" units sold, including one to
Dartmouth College Dartmouth College ( ) is a Private university, private Ivy League research university in Hanover, New Hampshire, United States. Established in 1769 by Eleazar Wheelock, Dartmouth is one of the nine colonial colleges chartered before the America ...
where students implemented Dartmouth ALGOL 30 and DOPE (Dartmouth Oversimplified Programming Experiment) on the machine.


Programming


Instruction set

The LGP-30 has 16 instructions. Each instruction occupies a 31-bit word though about half the bits are unused and set to zero. An instruction consists of an "order" such as the letter b for "bring from memory" and an address part such as the number 2000 to designate a memory location. All instructions have a similar appearance in an LGP-30 word. The order bits occupy positions 12 through 15 of the word and the address bits occupy positions 18 through 29 of the word. The address bits are further divided by track and sector. Although all instructions have an address, some do not use the address. It is customary to enter an address of 0000 in these instructions.


ACT-III programming language

The LGP-30 had a high-level language called ACT-III. Every token had to be delimited by an apostrophe, making it hard to read and even harder to prepare tapes:

s1'dim'a'500'm'500'q'500''
index'j'j+1'j-1''
daprt'e'n't'e'r' 'd'a't'a''cr''
rdxit's35''
s2'iread'm'1''iread'q'1''iread'd''iread'n''
1';'j''
0'flo'd';'d.''
s3'sqrt'd.';'sqrd.''
1'unflo'sqrd.'i/'10';'sqrd''
2010'print'sqrd.''2000'iprt'sqrd''cr''cr''
...


ALGOL 30

Dartmouth College developed two implementations of
ALGOL 60 ALGOL 60 (short for ''Algorithmic Language 1960'') is a member of the ALGOL family of computer programming languages. It followed on from ALGOL 58 which had introduced code blocks and the begin and end pairs for delimiting them, representing a ...
for the LGP-30. Dartmouth ALGOL 30 was a three-pass system (compiler, loader, and interpreter) that provided almost all features of ALGOL except those requiring run-time storage allocation. SCALP, a Self Contained Algol Processor, was a one-pass system for a small subset of ALGOL (no blocks other than the entire program), no procedure declarations, conditional statements but no conditional expressions, no constructs other than while in a for statement, no nested switch declarations (nested calls are permitted), and no boolean variables and operators. As in ACT-III, every token had to be separated by an apostrophe.


DICTATOR

DICTATOR is a painful acronym for DODCO Interpretive Code for Three Address with Technical Optimum Range. DICTATOR, introduced in 1959, is an interpreter designed to hide the LGP-30 machine details from the programmer. The programming language resembles three-operand assembly code with two source operands and one destination operand. All numbers are in floating point with an eight digit mantissa and two digit exponent. Natural logs and exponents are supported along with sin, cos, and arctan. Up to four nested loops are supported. Table look-up and block memory move operations are implemented. A bit more than half the total LGP-30 memory is used by the interpreter; it takes about 30 minutes to load the paper tape via the Flexowriter. Floating point add, subtract, multiply, and divide take less than 455 milliseconds each. Cosine is calculated in 740 milliseconds.


Starting the machine

The procedure for starting, or "
booting In computing, booting is the process of starting a computer as initiated via Computer hardware, hardware such as a physical button on the computer or by a software command. After it is switched on, a computer's central processing unit (CPU) h ...
" the LGP-30 was complicated. First, the bootstrap paper tape was snapped into the console typewriter, a Friden Flexowriter. The operator pressed a lever on the Flexowriter to read an address field and pressed a button on the front panel to transfer the address into a computer register. Then the lever on the Flexowriter was pressed to read the data field and three more buttons were pressed on the front panel to store it at the specified address. This process was repeated, maybe six to eight times, and a rhythm was developed: burrrp, clunk, burrrp, clunk, clunk, clunk, burrrp, clunk, burrrp, clunk, clunk, clunk, burrrp, clunk, burrrp, clunk, clunk, clunk, burrrp, clunk, burrrp, clunk, clunk, clunk, burrrp, clunk, burrrp, clunk, clunk, clunk, burrrp, clunk, burrrp, clunk, clunk, clunk. The operator then removed the bootstrap tape, snapped in the tape containing the regular loader, carefully arranging it so it would not jam, and pressed a few more buttons to start up the bootstrap program. Once the regular loader was in, the computer was ready to read in a program tape. The regular loader read a more compact format tape than the bootstrap loader. Each block began with a starting address so the tape could be rewound and retried if an error occurred. If any mistakes were made in the process, or if the program crashed and damaged the loader program, the process had to be restarted from the beginning.


LGP-21

In 1963, Librascope produced a transistorized update to the LGP-30 named the LGP-21. The new computer had about 460 transistors and about 375 diodes. It cost only $16,250, one-third the price of its predecessor. However, it was also about one-third as fast as the earlier computer. The central computer weighed about , the basic system (including printer and stands) about .


RPC 4000

Another, more-powerful successor machine, was the General Precision RPC 4000, announced in 1960. Similar to the LGP-30, but transistorized, it featured 8,008 32-bit words of memory drum storage. It had 500 transistors and 4,500 diodes, sold for $87,500 and weighed .


Notable uses

Edward Lorenz used the LGP-30 in his attempt to model changing weather patterns. His discovery that massive differences in forecast could derive from tiny differences in initial data led to him coining the terms ''
strange attractor In the mathematics, mathematical field of dynamical systems, an attractor is a set of states toward which a system tends to evolve, for a wide variety of starting conditions of the system. System values that get close enough to the attractor va ...
'' and '' butterfly effect'', core concepts in
chaos theory Chaos theory is an interdisciplinary area of Scientific method, scientific study and branch of mathematics. It focuses on underlying patterns and Deterministic system, deterministic Scientific law, laws of dynamical systems that are highly sens ...
. The RPC-4000 (successor to the LGP-30) is also remembered as the computer on which Mel Kaye performed a legendary programming task in
machine code In computer programming, machine code is computer code consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). For conventional binary computers, machine code is the binaryOn nonb ...
, retold by Ed Nather in the hacker epic '' The Story of Mel''.


Simulation

A software simulation of the LGP-30 and LGP-21 are supported by SIMH, a free and open source, multi-platform multi-system emulator.


See also

*
IBM 650 The IBM 650 Magnetic Drum Data-Processing Machine is an early digital computer produced by IBM in the mid-1950s. It was the first mass-produced computer in the world. Almost 2,000 systems were produced, the last in 1962, and it was the firs ...
* List of vacuum-tube computers


Further reading

* *


References


External links


Working LGP-30 on display in Stuttgart, Germany



LGP-21 description

1962 advertisement showing both the LGP-30 and RPC-4000


* ttp://ed-thelen.org/comp-hist/lgp-30-man.html Programming manual
Warming up the LGP-30
on
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technikum 29: LGP 30


– company newsletters on LGP-30: * * {{commons category Vacuum tube computers Serial computers Typewriters