Ferranti Mercury
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The Mercury was an early commercial
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 ...
from the mid-1950s built by
Ferranti Ferranti International PLC or simply Ferranti was a UK-based electrical engineering and equipment firm that operated for over a century, from 1885 until its bankruptcy in 1993. At its peak, Ferranti was a significant player in power grid system ...
. It was the successor to the Ferranti Mark 1, adding a floating point unit for improved performance, and increased reliability by replacing the Williams tube memory with core memory and using more solid-state components. The computer had roughly 2000
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 (mostly type CV2179/A2134 pentodes, EL81 pentodes and CV2493/ECC88 double triodes) and 2000 germanium diodes. Nineteen Mercuries were sold before Ferranti moved on to newer designs.


Predecessor: Mark I

When the Mark I started running in 1951, reliability was poor. The primary concern was the
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 ...
system, which broke down all the time. Additionally, the machine used 4,200
thermionic valve Thermionic emission is the liberation of charged particles from a hot electrode whose thermal energy gives some particles enough kinetic energy to escape the material's surface. The particles, sometimes called ''thermions'' in early literature, ar ...
s, mostly EF50 pentodes and diodes that had to be replaced constantly. The Williams tubes, used as
random-access memory Random-access memory (RAM; ) is a form of Computer memory, electronic computer memory that can be read and changed in any order, typically used to store working Data (computing), data and machine code. A random-access memory device allows ...
and registers, were reliable but required constant maintenance. As soon as the system went into operation, teams started looking at solutions to these problems. One team decided to produce a much smaller and more cost-effective system built entirely with
transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
s. It first ran in November 1953 and is believed to be the first entirely transistor-based computer.
Metropolitan-Vickers Metropolitan-Vickers, Metrovick, or Metrovicks, was a British heavy electrical engineering company of the early-to-mid 20th century formerly known as British Westinghouse. Highly diversified, it was particularly well known for its industrial el ...
later built this commercially as the
Metrovick 950 The Metrovick 950 was a transistorized computer, built from 1956 onwards by British company Metropolitan-Vickers, to the extent of sixDavid P. Anderson, ''Tom Kilburn: A Pioneer of Computer Design'', IEEE Annals of the History of Computing - V ...
, delivering seven. At the time, transistors were very expensive, compared to tubes.


Prototype: Meg

Another team, including the main designers of the Mark I, started with a design very similar to the Mark I but replacing valves used as
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 with solid-state diodes. These were much less expensive than transistors, yet enough of them were used in the design that replacing just the diodes would still result in a significant simplification and improvement in reliability. At that time computers were used almost always in the sciences, and they decided to add a
floating-point In computing, floating-point arithmetic (FP) is arithmetic on subsets of real numbers formed by a ''significand'' (a Sign (mathematics), signed sequence of a fixed number of digits in some Radix, base) multiplied by an integer power of that ba ...
unit to greatly improve performance in this role. Additionally the machine was to run at 1 MHz, eight times faster than the Mark I's 125 kHz, leading to the use of the name megacycle machine, and eventually Meg. Meg first ran in May 1954. The use of solid-state diodes reduced valve count by well over half, reducing the power requirement from the Mark I's 25 kW to the Meg's 12 kW. Like the Mark I, Meg was based on a 10-bit "short word", combining two to form a 20-bit address and four to make a 40-bit integer. This was a result of the physical properties of the Williams tubes, which were used to make eight ''B-lines'', or in modern terminology, accumulator/
index register An index register in a computer's central processing unit, CPU is a processor register (or an assigned memory location) used for pointing to operand addresses during the run of a program. It is useful for stepping through String (computer science ...
s. Meg could multiply two integers in about 60 microseconds. The floating-point unit used three words for a 30-bit mantissa, and another as a 10-bit exponent. It could add two floating-point numbers in about 180 microseconds, and multiply them in about 360 microseconds.


Commercial version: Mercury

Ferranti, which had built the Mark I for the university, continued development of the prototype Meg to produce the Mercury. The main change was to replace the Williams tubes with core memory. Although slower to access, at about 10 μs for a 10-bit short word, the system required virtually no maintenance, considerably more important for commercial users. 1024×40-bits of core were provided, backed by four drums each holding 4096×40-bits. The first of an eventual 19 Mercury computers was delivered in August 1957. Manchester University received one in February 1958, leasing half the time to commercial users via Ferranti's business unit. Both
CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...
at Geneva and the
Atomic Energy Research Establishment The Atomic Energy Research Establishment (AERE), also known as Harwell Laboratory, was the main Headquarters, centre for nuclear power, atomic energy research and development in the United Kingdom from 1946 to the 1990s. It was created, owned ...
at Harwell also installed theirs in 1958. A Mercury bought in 1959 was the UK Met Office's first computer. The University of Buenos Aires in Argentina received another one in 1960. The machine could run Mercury Autocode, a simplified coding system of the type later described as a
high-level programming language A high-level programming language is a programming language with strong Abstraction (computer science), abstraction from the details of the computer. In contrast to low-level programming languages, it may use natural language ''elements'', be ea ...
. Detailed information both about the Mercury hardware and the Autocode coding system is included in a downloadable Spanish-language Autocode manual. Mercury weighed .


See also

* Manchester computers * List of vacuum tube computers


References


Further reading

* (NB. Has info on the character set.)


External links


MEG/MercuryInstallation of the Ferranti Mercury computer at CERN
{{CPU technologies Early British computers Mercury Vacuum tube computers