Milestone-Proposal:Manchester Code

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Docket #:2024-33

This proposal has been submitted for review.

To the proposer’s knowledge, is this achievement subject to litigation? No

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes

Has the IEEE Section(s) in which the plaque(s) will be located agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes

Year or range of years in which the achievement occurred:

1948-1949

Title of the proposed milestone:

Manchester Code, 1948-1949

Plaque citation summarizing the achievement and its significance; if personal name(s) are included, such name(s) must follow the achievement itself in the citation wording: Text absolutely limited by plaque dimensions to 70 words; 60 is preferable for aesthetic reasons.

In this building in 1948-1949 Manchester code was invented for reliably encoding digital data stored on the Manchester Mark I computer’s magnetic drum. It became a standard for computer magnetic tapes and floppy disks, and was used in digital communications including the Voyager 1 and 2 spacecraft and early Ethernet networks. It found wide use in domestic remote controllers, Radio Frequency Identification (RFID) tags, and many control network standards.

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.

Manchester code (originally known as Phase Encoding) is a line code that enables digital data to be transmitted through channels that will not pass DC, including inductive systems for the storage of digital data on magnetic materials. Manchester code is so named because it was invented at Manchester University for one of the first working magnetic drum stores to be integrated into a functional electronic computer in 1949: the Manchester Mark I.

Manchester code was subsequently used in magnetic data storage devices such as drums, and especially tapes. It was adopted as the data representation scheme in the international standard for digital information interchange on 1600 bits per inch tape in the 1970s, and as the standard for Single Density floppy disks.

Manchester code works by introducing signal transitions at the clock frequency. This enables a clock signal to be regenerated from the encoded data during replay or reception so that the individual bits can be discriminated. This embedded clock makes Manchester code very useful in digital communications where it has been widely used, for example in 10 Mbit/s Ethernet networks. Although more advanced codes that require lower bandwidth were developed subsequently, Manchester code’s simplicity means that it is still used in low-complexity systems such as consumer IR devices, RFID and near-field communication. Many years after its invention Manchester code continues to have a broad global impact.

IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.

IEEE Magnetics Society IEEE Communications Society IEEE Computer Society

In what IEEE section(s) does it reside?

United Kingdom and Ireland (UKRI)

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: United Kingdom and Ireland
Senior Officer Name: Professor Rod Muttram FREng, SMIEEE

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: United Kingdom and Ireland
Senior Officer Name: Professor Rod Muttram FREng, SMIEEE

IEEE section(s) monitoring the plaque(s):

IEEE Section: United Kingdom and Ireland
IEEE Section Chair name: Paul Cunningham

Milestone proposer(s):

Proposer name: Professor (Emeritus) Jim Miles
Proposer email: Proposer's email masked to public

Proposer name: Professor Thomas Thomson SMIEEE, FInstP
Proposer email: Proposer's email masked to public

Proposer name: Professor (Emeritus) Simon Lavington, CEng, FIET, FBCS
Proposer email: Proposer's email masked to public

Proposer name: Professor (Emeritus) Roland Ibbett FRSE, FBCS, CEng, SMIEEE
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):

Bridgeford Street, Manchester M13 9PL, UK; 53.46642; -2.23506

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. The plaque will be mounted on the outside of the Coupland 1 Building, Bridgeford Street, Manchester. This is a University building that now houses the Department of Psychology but was formerly the Department of Electrotechnics, and is the building within which the invention was made.

Are the original buildings extant?

Yes.

Details of the plaque mounting:

Coupland I Building formerly housed the Department of Electrotechnics and was the building in which Manchester code was invented. The plaque will be on the outside wall of the building on Bridgeford Street, shown below. The plaque will be adjacent to the existing IEEE Milestone plaque for the Manchester Baby and Mark I computers which is on the outside of the rooms in which both inventions were made.

The outside of the Coupland I Building from Bridgeford Street. The plaque for Manchester code would be placed to the right of the existing IEEE Milestone plaque for the Baby computer

How is the site protected/secured, and in what ways is it accessible to the public?

It will be bolted to the wall at a height where it is readily visible to the public. Bridgeford Street is a well-used public right of way through the University campus with no restrictions and is a main walking route to the nearby Trinity High School, an 11-18 school based in the local community. University security staff patrol the campus on foot 24 hours a day. The existing IEEE Milestone plaque has been in position since June 2022 without problem.

Who is the present owner of the site(s)?

The University of Manchester

What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include detailed support at the end of this section preceded by "Justification for Inclusion of Name(s)". (see section 6 of Milestone Guidelines)

Historical Significance

Manchester code or Phase Encoding is a “line code” – a way of representing digital data that enables it to be transmitted and received, or stored and retrieved. Manchester code is so named because it was invented at Manchester University in the United Kingdom, by Prof. F.C. Williams. Williams’ student G.E. “Tommy” Thomas used it as a key component of one of the first working magnetic drum stores to be integrated into a functional electronic computer, developed for the Manchester Mark I computer before March 1949 and a part of the operational computer by June 1949. The patent for Manchester code was applied for in Williams’ name alone in March 1949 and was published in April 1954 [1].

Manchester code was invented as a format for storing digital information on the magnetic surface in a drum store. Digital data may contain very long strings of ‘1’s or ‘0’s and the devices used in Manchester would not function with such D.C. (Direct Current – continuous, or steady-state) signals. Data therefore had to be encoded into a DC-free form before storage, and Manchester coded data was designed to have no DC and very little low-frequency information. Manchester code was subsequently used in magnetic data storage devices such as drums and especially tapes, being adopted as the data representation scheme in the international ANSI-INCITS 39 standard for digital information interchange on 1600 bits per inch tape in the 1970s [2] [3] and as the standard line code for Single Density floppy disks.

Manchester code works by introducing signal transitions at the clock frequency and this enables a clock signal to be regenerated from the encoded data during replay or reception so that individual bits can be discriminated. This feature subsequently made Manchester code very useful in digital communications where it has been widely used, including by the Voyager 1 and Voyager 2 spacecraft and also in the first Ethernet ANSI/IEEE 10 Mbit/s standards derived from the "Blue Book" [4]. The IEEE Ethernet LAN standards are themselves an IEEE Milestone. Although more advanced codes were subsequently developed for high performance applications, Manchester code’s simplicity means that it is still used in common consumer devices such as TV remote controllers, Radio Frequency Identification (RFID) tags, and small-scale systems such as computer controlled lighting and in-vehicle networks [5].

Decades after its invention Manchester code continues to have a broad global impact, enabling many commonplace consumer products to function.

What obstacles (technical, political, geographic) needed to be overcome?

Obstacles That Needed to be Overcome

The Invention of Manchester Code

By the end of World War 2 (WW2) electronics had advanced to the point that a fully electronic stored program computer was feasible, and several groups began working on the problem of building one. It was widely acknowledged that digital storage was the major challenge. The first computer to execute a program stored in addressable read-write electronic memory was the Manchester “Baby” or Small-Scale Experimental Machine, which ran its first program on 21st June 1948, and is recognised as an IEEE Milestone. All groups striving to build electronic computers at the time realised that addressable electronic-speed memory was too expensive per bit to provide in anything but modest capacities and that they would additionally require larger secondary or “subsidiary” stores costing less per bit. Magnetic drum storage, in which a drum coated with magnetic material is rotated under one or more “heads” that detect the magnetic state of the drum surface) had been patented by Tauschek of IBM in 1933 [6]. By the end of the second world war magnetic technology had advanced to the point that it was feasible to build a magnetic drum to serve as a secondary store and multiple groups began research, including Harvard [7], Princeton [8], The University of Illinois [9], The National Bureau of Standards [10], CSIRO Australia [11], Birkbeck College, England [12], Northrop [13], and Engineering Research Associates (ERA) [14]. Of these, ERA had a working prototype drum store by 19th June 1947 [15] while in the UK Booth recalled that Birkbeck College had a working drum store by February 1948 [16].

Figure 1: An example data stream (0101110001) encoded by different line codes, with the blue lines showing the encoded signal and the vertical black lines showing the boundaries of the bit cells: a) Unencoded data; b) Dipole or Return to Zero (RZ); c) Unipolar Return to Zero; d) Non-Return to Zero (NRZ); e) Manchester code; f) Differential Manchester code.

There were two line codes in use in early drum stores: Return to Zero (RZ) and Non-Return to Zero (NRZ), shown in Figure 1. These are categorised as line codes but in fact there is no encoding, the binary data is just represented as it is, with a ‘0’ represented by a signal (current or voltage) in one direction and a ‘1’ by a signal in the opposite direction. Time (or distance down-track in a magnetic store) is divided up into segments, one for each bit, called bit cells. In NRZ the signal is maintained in the appropriate direction for the entire bit cell so that signal only changes if the binary value changes at a bit-cell boundary. In RZ the signal always returns to zero within the bit cell so that each bit appears as a signal pulse, either positive or negative. In magnetic recording RZ results in a magnetized region within each bit cell, polarised either in one direction or the other, i.e. a magnetic dipole for each bit. RZ was therefore called dipole recording by some groups working on early drum stores. Research groups at the time were employing either RZ or NRZ and none had identified a need for a different line code. Return to Zero (RZ) was used in the Harvard Mark III [7], the Princeton IAS machine [8], Booth’s ARC machine [12] and the IBM 650 drum [17]. Non-Return to Zero (NRZ) was used in the Northrop MADDIDA [13] and ERA drums [14].

Figure 2: G.E. (Tommy) Thomas working on the Ferranti-re-engineered drum store c1949. The drum shown was used as a prototype, the data stored on it being the first instance of Manchester code. It was then used in the University-designed and -constructed Manchester Mark I computer until the commercial Ferranti Mark I computer replaced it. The drum was subsequently reused by Dick Grimsdale as the memory of his experimental Transistor Computer (November 1953) which was commercialised by Metropolitan Vickers as the Metrovick 950 in 1956.

Around February 1948 [18] the Manchester University team realised that their developing computer would require a subsidiary magnetic drum store to supplement its random-access electronic memory, and F.C. Williams and Cliff West began work by building a rotating drum mechanism with a servo-controlled motor. In September 1948 G.E. (Tommy) Thomas began an MSc project supervised by F.C. Williams, the aim being to make the drum into a working store for the Manchester Mark I computer.

When building their drum store the Manchester group did not seek to reinvent the wheel, and made use of all available information, citing work by Princeton [8], ERA [14], Harvard [19] and Birkbeck [12], as well as publications by Komei [20], Sheppard [21] and Chu [22], and the Manchester group made no claim that the magnetic or mechanical designs of their drum store were original. To build their prototype drum, Williams and Thomas elected to use a nickel-plated drum as the storage medium, as used by Booth of Birkbeck, who later observed that this was the only available means of coating a magnetic drum in the UK at that time [16], powdered ferrites only being available in the USA. They also used single turn record/replay heads, which had been proposed and investigated by Bigelow of Princeton [8] and adopted by Booth of Birkbeck [12][23] to enable high frequency operation. Single turn recording heads require a high electric current in order to generate a large enough magnetic field to imprint the required magnetisation on the storage medium on the surface of the drum, and the Manchester heads required 15A in order to magnetize the nickel thin film coating. At that time the vacuum electronic devices available could not generate such high currents and so a current transformer was required to boost the current for recording.

Transformers will not function with steady-state (Direct Current or DC) signals. Because data in a computer could take any form and might include long strings of ‘0’s or ‘1’s which would not pass through the transformer it was necessary for the Manchester team to find a way to encode the data into a form where the signal had no DC component – i.e. an average value of zero, regardless of the data pattern to be stored. Existing line codes had been compared by ERA in order to select one for use in their drum stores but ERA used recording heads with 100 turns[8] that would only have needed a current of 150 mA, which was achievable without the use of a transformer. ERA therefore did not need to find a way to remove the DC from their written data and were able to use existing codes. ERA concluded that Non-Return to Zero (NRZ) was better than RZ to store data on their drum because NRZ only required half the number of signal changes for the same data pattern, and there is no evidence that they considered any other line codes for their drum stores.

The Manchester group had access to the ERA group’s 1947 report[8], and they used a graphical analysis similar to that of the ERA group to compare different codes, but they had to invent a new code with zero DC component. To satisfy this requirement F.C. Williams invented Manchester code, which he called Phase Encoding, to do the job, and Tommy Thomas built it into the Manchester prototype drum store.

Storage System Development

The Manchester drum store was designed to be a subsidiary store for the Manchester Mark I computer whose primary data storage was in random access Williams-Kilburn Cathode-Ray Tubes (CRTs). Each CRT stored 32 40-bit words, arranged on the CRT screen as 32 lines with 40 bit positions on each line. The data stored in a Williams Kilburn store could be made visible by attaching a second CRT that replicated the contents of the store but without a detector on the front of the screen, so that the stored data could be seen by the user as 32 lines, each with 40 bits on it (one word). Perhaps because the information was both arranged as and could be seen as lines of words the contents of a CRT store were collectively referred to as a “page”, a page being 32 words of 40 bits, i.e. 1,280 bits. The use of the word “page” to describe a block of data was adopted by members of the Manchester group very early in the development of modern computers. Coincidentally, Alan Turing had used the analogy of books and pages in February 1947 [24]when describing the notional difficulty of speeding access to individual items in a large collection of information.

The Drum store was designed to store 2 pages on each track, and its speed was servo controlled such that the bit frequency and phase exactly matched the main machine clock. Therefore a page of data could be transferred from CRT to drum or vice-versa, with the data transferring synchronously at the data rate of the main machine. The Mark I drum was designed so that only transfers of whole pages could be made, with instructions (“order codes”) provided to allow such page transfers. The programmer was responsible for deciding what information was required to be in the primary (random access, fast) CRT stores at what times, and to encode the necessary page transfers into their program. To help with this, an extra line on the CRT screen was used to display the position of the associated page on the drum backing store [25]. This is thought to be the first instance of paging in a modern computer. The fact that the Manchester machines were designed to move whole pages of memory between primary and subsidiary store to enable the programmer to use a much larger memory than the primary store provided is a very early instance of systems integration and will have strongly contributed to Kilburn’s thinking about the organisation of memory. Automation of this process probably led to Kilburn’s later invention of the “One Level Store”, or Virtual Memory which is recognised as an IEEE Milestone.

The Inventor of Manchester Code

Although Manchester code is often attributed to Thomas, since it was first published in his single-author 1949 paper at the Cambridge conference[26] and in his MSc dissertation[27], it was actually invented by his supervisor, F.C. Williams. The patent for Manchester code[1] was applied for and granted in Williams’ name alone, which would not have happened had Thomas invented it – Thomas was named on two other patent applications covering work to which he contributed. Dai Edwards, who was a contemporary MSc student with Thomas, working in the same lab, gave his Digital Pioneer Computer lecture in 1981 in which he said “F.C. came up with the phase modulation system” (time 37’ 30”). Dai would have known who had had the idea and Dai would have attributed it to Thomas had Thomas been the inventor. In 2000 Thomas corresponded with Forster[28] and stated that Williams introduced him to Phase Encoding (Manchester code). It is therefore clear that Manchester code was invented by F.C. Williams, the first instantiation of it being built by Thomas.

Variants of Manchester Code

In Manchester code the data bits are encoded as transitions rather than as values. In its original form a data value of ‘0’ is encoded as a positive or rising transition at the centre of the bit cell while a ‘1’ is encoded as a negative or falling transition. Successive data bits of the same value require an additional transition to be inserted at the boundary of the bit cells. In the IEEE standards that employ Manchester code the opposite polarity is used: for data value ‘1’ the transition is low-high at the centre of the bit cell and for ‘0’ high to low.

Differential Manchester code is a variant of Manchester code; both are shown in Figure 1. In Manchester code’s original form regularly spaced transitions whose polarity represents the data values are required, one in every bit cell, and additional transitions must be added between adjacent bits of the same data value. In Differential Manchester code the regularly spaced transitions, one of which must be present in every bit cell, are interpreted as the clock and an extra transition is added between them if the data has a specified data value (‘0’ or ‘1’), while no extra transition is added for the other data value. Encoding the data as the presence or absence of a transition rather than the polarity of the transition is advantageous because it makes Differential Manchester code immune to inadvertent signal inversion.

Two main variants of Differential Manchester code exist, in one of which an encoded data transition denotes a ‘1’ and no transition denotes a ‘0’ (“Biphase Mark” or “Biphase-M”), and in the other a transition denotes a ‘0’ and no transition denotes a ‘1’ (“Biphase Space” or “Biphase-S”). Biphase-M is also referred to in magnetic recording as Frequency Modulation (FM), so named because a ‘1’ has double the transition rate (or frequency) of a ‘0’. In other contexts Differential Manchester code is also referred to as F2F (frequency/double frequency), Aiken biphase, and conditioned diphase.

Advantages and Disadvantages

The main advantage of Manchester code is that it contains no DC and only very low amounts of low frequencies and thus it is very well suited to magnetic recording and to communication channels without galvanic connection. Also, Manchester code has transitions in the encoded data pattern at the clock frequency, i.e. the transmitted signal is a combination of the clock and the data. Because Manchester code has a transition in every bit cell (unlike some more efficient codes), a clock is readily regenerated from the received data stream and thus Manchester code is robust in the presence of noise. Manchester code’s disadvantage is that it requires up to two transitions per data bit and thus cannot store data at the same density as either NRZ or more complex codes.

What features set this work apart from similar achievements?

Features That Set the Work Apart

The invention of Manchester code came at a time when no other groups working on magnetic drum stores were considering new line codes. The other groups at the time were using simple existing codes that were sufficient for those specific devices but whose DC content and lack of an embedded clock meant that their future impact, particularly in digital communications, would have been less significant. Manchester code, with no DC and with an embedded clock, set the core requirements for future line codes for magnetic recording and digital communications.

Why was the achievement successful and impactful?

The Impact of Manchester Code

Overview

The first advantage of Manchester code is that its signal has no DC content, and very low signal content at low frequencies, which made it very well suited to magnetic recording. The second advantage is that, because at least one signal transition is created in each bit cell or clock period, the clock is effectively embedded within the encoded signal. This was not a requirement for the Manchester group because the Mark I computer ran its primary and subsidiary stores from the same machine clock, but in most magnetic storage systems the store does not have access to the system clock when recorded data is being read. The fact that in Manchester code the clock and the data are merged into the signal is what enables the data to be decoded when it is read, and this proved to be a great advantage and an essential feature of all subsequent digital recording systems.

As well as being suitable for magnetic recording systems, Manchester code’s advantages make it very suitable for data communication where the requirement of a single channel of communication for both data and clock, simplicity of implementation and robustness are all important, and Manchester code has been extensively used in communication, where it has had great impact.

Manchester code is rather inefficient because it introduces many additional signal transitions, in the worst case doubling the number of signal transitions required to record or transmit the data. More efficient codes have been invented and these are used wherever the maximum data rate is important. However Manchester code is very simple to implement and its large number of transitions does mean that recovering the clock is relatively easy, making it robust. Manchester code is therefore very useful in situations where simplicity of implementation and robustness are of primary importance and the required data rate is low for the available bandwidth.

Magnetic Recording

In magnetic recording Manchester code was initially used in some drum stores, particularly early Ferranti drum stores such as the Pegasus computer (1956), and some other manufacturers such as Metropolitan Vickers in their Metrovick 950 [29] (page 8). Bryant’s 1966 Auto-lift Magnetic Drum Stores were available with a choice of either Phase Encoding (Manchester code) or NRZI encoding [30] (footnote p4). It was also used in some hard disk drives until around 1971 when IBM introduced Modified Frequency Modulation (MFM), an evolution of FM (Differential Manchester code), for the IBM 3330 drive [31].

Manchester code’s robustness, particularly its high proportion of clock transitions compared to data, made it well suited to systems with removable media, where media might be exchanged between different systems, as clock recovery and thus decoding is more reliable.

Magnetic Tapes

Manchester code (known at the time as Phase Encoding or PE) was used in 1600 bits per inch (bpi) 9-track tape in the IBM 2400 series tape decks for the System/360, which was introduced in 1964. 1600 bpi 9-track tape stored 45MB on a tape with the usual length of 2,400 feet (730 m). 1600bpi using Manchester code (PE) continued to be supported in subsequent IBM tape decks such as the 3400 series for the System /370, until as late as the 1990s in the 9348-012 tape deck for the AS/400 series.

A standard was required and in 1970 Manchester code was the line code of the proposed standard for 1600 bpi 9-track tape [32], the standard being published in 1973 as ANSI-INCITS 39 [33]. Phase encoding was also required in the 1971 ECMA-36 European standard for 1600 bpi tape [34] and the 1976 International Standards Organisation (ISO) standard 3788. Manchester code was retained for 1600bpi in subsequent revisions of all the relevant US, European and International standards for 0.5” 1600bpi tape including ECMA-62 [35]. Manchester code was also used for data on tape cartridges, for example in the IEC standard for ¼” tape cartridges in 1986 and 0.150” tape cassettes. Manchester code (PE) was also used in DEC’s proprietary 420 bpi LINCtape and 375 bpi DECtape used in PDP computers from the PDP-4 onwards[36].

Because the 9-track 1600 bpi format using Manchester code (PE) was an American, European and international standard for information interchange, it was for some time almost universally used in magnetic tape data storage systems. It was such a universally accepted tape interchange standard that even when more advanced tape decks arrived with higher storage capacities, they would still provide backwards compatability to the 1600 bpi standard.

Floppy Disks

Differential Manchester code (Frequency Modulation or FM) was also used in the early Single Density (SD) 8” floppy disk drives. As floppy disks developed, MFM was introduced as a line code that enabled the higher storage density of “Double Density” (DD) 5.25” disks, though such drives also accepted SD disks for which they implemented the SD standard (i.e. Manchester code) for write and read, and SD (Manchester coded) 5.25” floppy disks were widely used.

Manchester code therefore underpinned important standards for removable magnetic storage media.

Digital Communication

Voyager Spacecraft

Manchester code has been and remains widely used in digital communication. It was employed for command signals sent to the two NASA space probes Voyager 1 and Voyager 2, launched in 1977. In 2017, 40 years after launch, the Voyager team successfully fired Voyager 1’s Trajectory Correction Maneuver (TCM) thrusters for the first time since 1980 by transmitting Manchester coded control signals to it. As of 2024, Voyager 1 and 2's communication systems were both still functional, the two spacecraft being 15.2 and 12.7 billion miles from Earth respectively. Signals from Voyager 1 take over 22 hours to reach Earth, with the received signal strength being below 9×10−8pW (-160.48 dBm). Voyager 2's trajectory has taken it below the ecliptic, meaning that communication is only possible via stations in the southern hemisphere. Voyager 2's communications are now handled by Deep Space Station 43 in Canberra, Australia. Station 43 is itself recognised as an IEEE Milestone.

Early Ethernet Networks

In 1973 Robert Metcalfe and David Boggs adopted Manchester encoding for the very first implementation of Ethernet, based on packet broadcasting on a shared 2.94 Mbit/s coaxial cable. Invented by Metcalfe and Boggs at the Xerox Palo Alto Research Center (PARC) in California, the Experimental Ethernet used Ethernet transceivers and single-card adaptors designed for PARC's pioneering Alto personal computer, which included a mouse and a graphical user interface (GUI). Metcalfe and Boggs chose Manchester encoding because simplicity of implementation was a design constraint. Manchester encoding and decoding circuits were simple and compact, clock recovery was easy because every bit cell contains a transition, and the encoded signal could be capacitively coupled onto the Ethernet cable due to the absence of low-frequency components.

By 1974 Ethernet was essential in the work environment of the PARC engineers who used Alto computers for communication with each other by email, for transferring files, and to access a laser printer. By 1975, a Data General Nova 800 minicomputer served as a gateway from the PARC Ethernet network to the ARPAnet, to Ethernets in nearby buildings, and to Ethernets in Xerox offices in Southern California, the US East Coast, the UK, and Sweden.

In 1979-1980 the first Ethernet networks outside of Xerox facilities were installed at Stanford University in California, Massachusetts Institute of Technology (MIT), and Carnegie Mellon University in Pennsylvania. Each site used 2.94 Mbit/s Manchester encoded Ethernet over coaxial cable to network 18 Alto computers and a laser printer. The Stanford network was called SUN (Stanford University Network), and this name and network led to the formation of Sun Microsystems.

Starting in 1977 Xerox System Development Department (SDD) employees began working with other companies to create an updated version of Ethernet for broad industry use. This work led to the 10 Mbit/s Ethernet 1.0 "Blue Book" specification which used Manchester code as the channel code, and which was jointly published in September 1980 by the “DIX” consortium consisting of Digital Equipment Corporation (DEC), Intel, and Xerox [4]. This specification became the basis for the IEEE 802.3 standard for 10 Mbit/s Ethernet LANs that was formally standardized in 1985. In anticipation of the standard, products supporting this specification began to emerge in 1981-1982 from companies primarily in Silicon Valley including 3Com, Ungermann-Bass, Sun Microsystems, Intel, and AMD, and also others including Interlan and Mostek.

Manchester code was then used in several important Ethernet standards: thick co-axial 10BASE5 (IEEE 802.3-1985); thin co-axial 10BASE2 (IEEE 802.3a); twisted pair 10BASE-T (IEEE 802.3i); and optical fiber 10BASE-F (IEEE 802.3j) Ethernet LANs. Thin co-axial 10BASE2 was the dominant Ethernet LAN cabling from the mid 1980s to around 1990. 10BASE-T, introduced in 1988, dominated until the mid-1990s. Differential Manchester code was specified in the IEEE 802.5 standard for token ring LANs, developed by IBM and used in IBM products from 1985-1990. In 1995 100 Mbit/s Ethernet was standardized by IEEE 802.3u which specified 4B5B and MLT-3 line codes in place of Manchester code. Thus Manchester code was the dominant line code in Ethernet LANs until 1995, and it continued to be used in legacy systems for some time after that. Differential Manchester code continues to find use in the 10BASE-T1S (automotive) and 10BASE-T1L (long distance) IEEE 802.3cg standard, approved November 2019.

Domestic Remote Controllers

Manchester code has been chosen for a wide range of standards for applications where simple and robust digital communication is required. Perhaps its most ubiquitous application is in the Philips RC-5 and RC-6 standards for consumer Infra–red (IR) remote handsets - standards that were adopted by most European manufacturers and many US manufacturers. It is used in consumer items such as TVs and other audio-visual equipment such as video recorders, video cameras, CD, DVD and Blu-ray disc players. It is estimated that the average US home has 4 remote handsets. Worldwide it is likely that Manchester code is in current use in over a billion such devices.

Control Network Standards

In the IEC 62386 DALI (Digital Addressable Lighting Interface) standard for digital communication between lighting-control devices [37] a 2-wire bus is used for communication of commands and data, with transmitted information being Manchester encoded. A point of local interest is that Manchester Airport uses DALI (and thus Manchester code) in its passenger terminals. Profibus is an open field bus standard for applications in manufacturing and process automation in which two protocols are defined: UART and MBPO, or Manchester coded Bus Powered Open. MBPO, as its name suggests, employs Manchester code as its line code.

PSI5 (Peripheral Sensor Interface 5) is an interface for automotive sensor applications that is based on worldwide interface standards for peripheral airbag sensors that use Manchester code to communicate. The PSI5 consortium includes leading manufacturers such as Bosch, Continental, Analog Devices, ST and many others. PSI5 is proven in millions of airbag systems, Manchester code being chosen because of its robustness [5].

MIL-STD-1553 is a U.S. DOD Military Standard. The interface allows for between 2 and 32 devices on the bus and Manchester code is used as the line code. The MIL-STD-1553 interface is widely used by all branches of the U.S. military and by NASA. Outside of the US it has been adopted by NATO as STANAG 3838 AVS and the UK MoD Def-Stan 00-18 Part 2. It has therefore been in widespread use in Western military equipment control systems, especially aerospace, but MIL-STD-1553 is now being replaced on newer U.S. designs by IEEE 1394.

RFID and Other Applications

Manchester code is specified for tag to reader communication in Type A Radio Frequency IDentification (RFID) cards that meet the ISO/IEC 14443 standard. ISO/IEC 14443 compliant cards are used in many systems including: transit payment cards; biometric passports; national identity cards in the European Economic Area; and Europay, Mastercard and Visa (EMV) payment cards.

Differential Manchester code is specified by ISO/IEC 7811 part 2 for use in low density, low coercivity magnetic stripes on cards. This standard was used in early implementations of bank cards [126] and for other card applications, though more modern cards use the high coercivity ISO/IEC 7811 part 6 or the high coercivity, high density ISO/IEC 7811 part 7 standards, for which data is encoded with MFM.

Manchester code was also used in the first series of Euro banknotes, which included a bar code in a vertical stripe to the right of the watermark. The bar code contained a 3-bit (€5 and €20 notes) or 4-bit (higher denominations) code, expressed in Manchester code with 01 (rising transition) for ‘1’ and 10 (falling transition) for ‘0’.

Manchester code is also used in AES3, S/PDIF, SMPTE time code, USB PD and xDSL.

Summary

In summary, Manchester code has had a significant impact in magnetic data storage and in communications. At the time of writing (2024) Manchester code remains in very widespread use in communication systems, 75 years after its invention.

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.

References

  1. ↑ 1.0 1.1 Williams Frederic Calland, UK Patent GB707634 (Also US Patent US2734186), “Magnetic Storage Systems”, UK application No. 5632/49 1st March 1949, Published April 21st 1954.
  2. ↑ “Proposed American National Standard: Recorded Magnetic Tape of Information Interchange”, pp. 679 – 685, Communications of the ACM, Vol 13, No 11, November 1970
  3. ↑ “Information systems - recorded magnetic tape for information interchange (1600 cpi, phase encoded)” ANSI-INCITS 39, published 1973
  4. ↑ 4.0 4.1 "The Ethernet: A Local Area Network - Data Link Layer and Physical Layer Specifications Version 1.0" Co-published by Digital Equipment Corp. (DEC), Intel, and Xerox (DIX) aka, the Ethernet 1.0 "Blue Book" (Sept. 30, 1980)
  5. ↑ 5.0 5.1 M. Baus, A. Hepp, J. Seidel, T. Weiss, A. Gesell, F. Ploetz, J.-P. Ebersohl, and M. Fischer, “Considerations on Functional Safety of the PSI5 Interface in the Scope of the ISO26262”, talk given at Safetech2012, Munich. https://www.psi5.org/fileadmin/user_upload/psi5/Home/PDFs/SafeTech2012_FuSi_PSI5_paper.pdf at 21st October 2024
  6. ↑ Tauschek, G. “Electromagnetic memory for numbers, and other data” US Patent 2,080,100 (Filed March 10 1933, Issued May 11 1937, German Patent DE643803C (Filed: July 1, 1933 Issued: April 17, 1937)
  7. ↑ 7.0 7.1 Staff of the Computation Laboratory, Harvard University, “Description of a Magnetic Drum Calculator”, Annals of the Computation Laboratory of Harvard University, vol. 25, 318 pages, 1952.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 J.H. Bigelow, P. Panagos, M. Rubinoff and W.H. Ware, “First Progress Report on a Multi-Channel Magnetic Drum Inner Memory for use in Electronic Digital Computing Instruments”, Institute for Advanced Study, Electronic Computer Project, Princeton, 1st July 1948. Reprinted by Forgotten Books, ISBN 978-1-330-61539-3, 2018
  9. ↑ "Preliminary Considerations On A Magnetic Drum Controlled Computer" Edward F. Moore and Theodore Shapin, Courtesy of the University of Illinois Archives, Record Series 11/15/9, Box 1, Folder ILLIAC Internal Reports Vol. 1 Nos. 1-36, Internal Report No. 26, February 3, 1951
  10. ↑ Harry D. Huskey, “The National Bureau of Standards Western Automatic Computer (SWAC)”, Annals of the History of Computing, vol. 2, no. 02, pp. 111-121, 1980.
  11. ↑ Brian F.C. Cooper, “A Magnetic Drum Digital Storage System”, Proceedings of the Institution of Radio Engineers Australia, Volume 14, No 7 p169 – 178, July 1953
  12. ↑ 12.0 12.1 12.2 12.3 A.D. Booth, “A Magnetic Digital Storage System”, Electronic Engineering, p. 233, Vol 21, July 1949. From http://www.bitsavers.org/pdf/univac/1101/ERA-1101-f13-MagneticDigital_Jul49.pdf
  13. ↑ 13.0 13.1 Donald E. Eckdahl, Irving S. Reed and Hrant H. (Harold) Sarkissian “West Coast Contributions to the Development of the General-Purpose Computer: Building Maddida and the Founding of Computer Research Corporation” IEEE Annals of the History of Computing, pp 4-33, January–March 2003
  14. ↑ 14.0 14.1 14.2 A.A. Cohen and W.R. Keye, “Selective Alteration of Digital Data in a Magnetic Drum Computer Memory”, Report by Engineering Research Associates Inc. to the Office of Naval Research, December 1947. https://apps.dtic.mil/sti/citations/AD0083915
  15. ↑ Sidney M. Rubens, “Data Storage on Drums”, in Daniel, Mee and Clark, “Magnetic Recording The First 100 years”, IEEE Press, ISBN 0-7803-4709-9, 1998
  16. ↑ 16.0 16.1 Andrew D. Booth, “Computers in the University of London, 1945-1962”, pages 551-561 in N. Metropolis, J. Howlett And Gian-Carlo Rota (Eds), “A History of Computing in the Twentieth Century” (papers presented at the International Research Conference on the History of Computing, held at the Los Alamos Scientific Laboratory, 10-15 June 1976), Academic Press Inc (Elsevier), ISBN: 978-0-12-491650-0, (1980) (see also the recording of Booth’s talk, dates on which key developments occurred are between 35’ and 40’ into the talk, discussion of magnetic coatings is at 16’ 33” into the recording)
  17. ↑ Page II-46 of “Customer Engineering Manual of Instruction, IBM 650 Data Processing System”, IBM, 1956
  18. ↑ Tom Kilburn, Audio interview conducted by David Reid, Local Heritage Librarian, Stockport Library, interview date 2nd April 1998. The tapes are held by Stockport Library, Stockport, UK.
  19. ↑ B.L. Moore, “Magnetic and Phosphor Coated Disks”, p130, in “Proceedings of a Symposium on Large-Scale Digital Calculating Machinery (7-10 January 1947)”, Annals of the Computation Laboratory, Harvard, Vol XVI, Sept 1948. Reprinted as Volume 7 of the Charles Babbage Institute Reprint Series for the History of Computing, MIT Press and Tomash Publishers, ISBN 0-262-08152-0, 1985.
  20. ↑ Otto Komei, “Survey of Magnetic Recording”, p223, in “Proceedings of a Symposium on Large-Scale Digital Calculating Machinery (7-10 January 1947)”, Annals of the Computation Laboratory, Harvard, Vol XVI, Sept 1948. Reprinted as Volume 7 of the Charles Babbage Institute Reprint Series for the History of Computing, MIT Press and Tomash Publishers, ISBN 0-262-08152-0, 1985.
  21. ↑ C.B. Sheppard, “Memory Devices”, in Lecture notes of a special course: “Theory and Techniques for Design of Electronic Digital Computers”, Moore School of Engineering, University of Pennsylvania, 8th July- 31st August 1946, Volume II. First published in mimeographed form by The Moore School of Engineering 1st November 1947. Edited and republished as “The Moore School Lectures”, Volume 9 in the Charles Babbage Institute Reprint Series for the History of Computing, pages 250-269, MIT Press and Tomash Publishers, ISBN 0-262-03109-4, 1985.
  22. ↑ Chuan Nun Chu, “Magnetic Recording”, in Lecture notes of a special course: “Theory and Techniques for Design of Electronic Digital Computers”, Moore School of Engineering, University of Pennsylvania, 8th July- 31st August 1946, Volume III. First published in mimeographed form by The Moore School of Engineering 30th June 1948. Edited and republished as “The Moore School Lectures”, Volume 9 in the Charles Babbage Institute Reprint Series for the History of Computing, pages 310-326, MIT Press and Tomash Publishers, ISBN 0-262-03109-4, 1985.
  23. ↑ A.D. Booth, Interview #9 in the ‘Pioneers of Computing’ series, Science Museum, London, Recorded by Christopher Evans for the Science Museum, published as 20 audio cassettes by Computer Capacity Management Limited Reading & Hugo Informatics, recorded at Los Alamos, 1976. https://collection.sciencemuseumgroup.org.uk/documents/aa110082041/set-of-20-interviews-on-audio-cassettes-pioneers-of-computing Copy also held in Store at Manchester University John Rylands University Library, Catalogue entry: UML copy at TRC 355: Imperfect: Wanting Nos. 2-5, 15, 18 and 20, MMS ID 992976843716701631.
  24. ↑ A.M. Turing, Lecture to the London Mathematical Society, 20th February 1947 https://www.vordenker.de/downloads/turing-vorlesung.pdf
  25. ↑ "Simon H. Lavington, “A History of Manchester Computers”, First edition, NCC Publications, 1975. pp. 20-24
  26. ↑ Thomas G.E. “Magnetic Storage”, Report of a Conference on High-Speed Electronic Calculating-Machines 22-25 June 1949, Cambridge, pages 75-80, January 1950
  27. ↑ Thomas G.E. “A Magnetic Storage System for Use With an Electronic Digital Computer”, MSc Thesis, 1950 https://archiveshub.jisc.ac.uk/manchesteruniversity/data/gb133-muc/5-9/muc/6/6
  28. ↑ Roger Forster, “Manchester encoding: opposing definitions resolved”, Engineering Science & Education Journal, Vol 9, Issue 6, pages 278-280, 2000.
  29. ↑ R. M. Foulkes, “Engineering Report 1026 Part 1. The Type 950 General Purpose Digital Computer Functional Design”, Metropolitan Vickers Electrical Company Limited, Manchester, England, December 1955. https://www.ancientgeek.org.uk/misc/Report_on_the_Metrovick_950.pdf
  30. ↑ Bryant Computer Products “Technical Data Auto-Lift Magnetic Storage Drums”, 1966. https://archive.org/download/TNM_Auto-Lift_Magnetic_Storage_Drums_from_Bryant__20170823_0078/TNM_Auto-Lift_Magnetic_Storage_Drums_from_Bryant__20170823_0078.pdf
  31. ↑ J.M. Harker, D.W. Brede, R.E. Pattison, G.R. Santana and L.G. Taft, “A Quarter Century of Disk File Innovation”, IBM Journal of Research and Development, Volume: 25, Issue: 5, pages 677-690, (September 1981). https://ieeexplore.ieee.org/document/5390599
  32. ↑ “Proposed American National Standard: Recorded Magnetic Tape of Information Interchange”, p679 – 685, Communications of the ACM, Vol 13, No 11, November 1970
  33. ↑ “Information systems - recorded magnetic tape for information interchange (1600 cpi, phase encoded)” ANSI-INCITS 39, published 1973. https://nvlpubs.nist.gov/nistpubs/Legacy/FIPS/fipspub25.pdf
  34. ↑ “Data interchange on 9-track magnetic tape at 63 bpmm (1600 bpi) phase-encoded”, ECMA-36, 1st edition, December 1971. https://ecma-international.org/publications-and-standards/standards/ecma-36/
  35. ↑ ECMA-62 “Data interchange on 12,7 mm 9-track magnetic tape - 32 ftpmm, NRZ1, 32 cpmm - 126 ftpmm, phase encoding, 63 cpmm - 356 ftpmm, NRZ1, 246 cpmm GCR”, 2nd Edition, March 1985. https://ecma-international.org/publications-and-standards/standards/ecma-62/
  36. ↑ Savard, John J. G. "Digital Magnetic Tape Recording". (2019) http://www.quadibloc.com/comp/tapeint.htm
  37. ↑ Wen Cheng Pu and Cheng Yu Tsai, “Development of Automatic Digital Control Interface for Addressing a Lighting Equipment System Using High Power Load, Sensors and Materials, Vol. 33, No. 6, 1829–1848 (2021)

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