Econet

This article is about the network system. For the mobile phone company, see Econet Wireless.

Econet

Econet upgrade manuals
Developer	Acorn Computers
Manufacturer	Acorn Computers
Type	Computer networking
Generation	8-bit
Operating system	MOS

Econet was Acorn's low-cost local area network system, intended for use by schools and small businesses. Econet is rumoured to be an abbreviation of Economy Network, but Acorn were always careful to stress the Greek root, oikos, meaning "house".^{[citation needed]}

Implementations

Econet was first introduced for use with the Acorn Atom and Acorn System 2/3/4 computers in 1981.

In 1982, the Education Department of Tasmania called a tender for the supply of personal computers to their schools. Earlier that year, Acorn's Australian computer distributor, Barson Computers, had released the Acorn BBC Microcomputer with disk storage as part of the bundle. Hermann Hauser and Chris Curry agreed to allow the BBC Micro to be offered with Econet fitted, as they had done with the Disc Filing System. Again they stipulated that Barson adapt the file system from the System 2 without assistance from Acorn. Barson's engineers applied a few modifications to fix bugs on the early BBC Micro motherboards. Those changes were adopted by Acorn in later releases. With both disk and networking available, the BBC Micro was approved for use in schools by all state and territory education authorities in Australia and New Zealand; and quickly overtook the Apple II as the computer of choice in private schools.

With no supporting documentation available, the head of Barson's Acorn division, Rob Napier, published "Networking with the BBC Microcomputer", Prentice Hall, 1984. This remains the only book published for the Econet.

Also in 1984, Econet was released for the BBC Micro in the UK and later became popular as a networking system for the Archimedes. The Econet system was eventually supported on all post-Atom Acorn machines except the Electron (except in Australia and New Zealand where Barson Computers built their own Econet daughter board), the A3010 and the eventually-cancelled Phoebe 2100.

The system was supported by Acorn MOS, RISC OS and RISC iX. Acorn received an offer from Commodore International to license the technology, which it refused.

An "Ecolink" interface card for IBM PCs was available. It used Microsoft's MS-NET Redirector for MS-DOS to provide file and printer sharing with the NET USE command.

Acorn Universal Networking (AUN) was an early 1990s implementation of Econet protocols and addressing over TCP/IP, to provide legacy support for Econet on Ethernet-connected machines.

The Econet protocol was also supported by the Linux kernel until May 18, 2012.

Physical layer

Econet DIN-5 Pinout

1	Data (+ve)
2	Ground
3	Clock (+ve)
4	Data (-ve)
5	Clock (-ve)

Econet is a 5-wire bus network. One pair of wires are used for the clock, one pair for data transmission and one wire is a common ground. Signalling was to the RS-422 5-volt differential standard, with one bit transfer per clock cycle. Unshielded cable was used for short lengths, and shielded cable for longer networks. The cable was terminated at each end to prevent reflections and to guarantee high logic levels when the bus was undriven.

The original connectors were five-pin circular 180° DIN types, although on later 32-bit machines (notably the A3020 and A4000) the Econet connection was available via five of the pins on the 15-pin D-type Network port, which could also accept MAUs (Media Attachment Units) to allow other network connections to be used with the same socket. This port looks similar to an AUI port, but is not compatible.

Each Econet interface was controlled by a Motorola MC68B54 Advanced Data Link Controller (ADLC) chip.

Each network segment had a maximum length of 500 meters, and could have up to 254 devices ("stations"). Machines and appliances such as filestores and bridges were configured with unique station numbers using jumpers or CMOS RAM settings. Network bridges, housed in a standard "BBC Cheese Wedge" box, were available for building larger networks; up to 127 segments could be bridged together.

The clock signal was generated either by a stand-alone clock box, by a BBC Microcomputer with a modified Issue 4 mainboard or by a Filestore fileserver. Only one clock generator could be used on each network. While the network was originally specified to run at 210 kHz, practical clock frequencies could range from about 40 kHz to around 800 kHz;^{[citation needed]} the presence of older machines on the network or the capacitance of a long network cable would reduce the maximum data rate reliably available.

Connections were established using a four-way handshake. The sender would broadcast.

Services

Being a proprietary network system and protocol, the services available on an Econet while standard in function, were to an extent unique in implementation, particularly in early versions of the file server software.

As Econet was intended as a low-cost local area network, there were only two services that could be expected of a standard Econet network. Acorn provided software for BBC Micro computers to primarily implement a file server, with an optional extra of a printer server. Acorn's tradition of providing full access to the operating system meant that numerous additional services could be added. Computing magazines of the time often carried short utilities such as network chat programs that made use of the Econet protocols without interfering with the basic file and print services.

The original file server was very basic, and essentially implemented network access to a floppy disk. Acorn developed their server software over many years, ending with the Level 4 File Server being the final release. Server software was also provided in the dedicated FileStore units Acorn produced.

Other manufacturers (in particular SJ Research) also produced Econet server hardware which implemented its own versions of the server software. These were compatible with the Acorn implementation, but with additional enhancements.^{[citation needed]}

Comparison with modern systems

While Econet can be considered unique amongst network systems and specific to the Acorn range of computers, it does share many commonalities with modern network file systems and protocols:

• Remote Procedure Call - Almost all network operations were performed via a primitive remote procedure call system, either by passing a command line direct to the file server, or by passing an operating system call parameter block. The logon command *I AM was processed by passing the whole command line and reading back the result code.

• Access Permissions - By the time of the Acorn Level 4 File Server and the SJ Research MDFS systems, Econet file servers had a full user name and password system with public and private attributes. These worked similar to Unix permissions without the group field. Files could be set to be readable and/or writable by everyone, just by the user, or both.

• Subnetting - A basic Econet would be a single network segment, which is usually assumed to be network 0. With the use of one or more bridges, it is possible to have up to 127 Econet segments with up to 254 hosts each, for a maximum of 32,258 possible machines.

• Broadcasting - By using host 255, an Econet host could send broadcast packets to all hosts on the network segment. Later implementations of the client software used this to automatically locate file and printer servers.

• Printer Spooling - Later versions of the Econet printer server software used printer spooling to locally cache print jobs before sending to the local printer. This ensured whole print jobs were sent to the printer in one go.

• Ports - Because the various protocols (file and printer servers, bridge discovery, and so forth) used clearly defined ports [1], it was quite possible to create additional services, such as BroadcastLoader, AppFS, teletext server, and a range of home grown chat programs and multiplayer games to coexist within the Econet system.

End of Econet

The Econet hardware implementation started to disappear from new Acorn machines around 1993 with the Risc PC machines. Previous machines had the capability to accept Econet modules as add ons via an adaptation of the connector used in BBC Master computers. The Risc PC range used a new network slot connector that would not accept the modules, though a later Econet module was in fact manufactured for this new connector.

The Econet software had mainly moved onto the AUN system by this time, though some suppliers were still offering bridging kits to join old and new together. Econet/AUN was largely superseded by the Acorn Access+ software that operated using native Ethernet and TCP/IP rather than simulating Econet traffic over a UDP system. This is turn was superseded by native support for more standard protocols such as Sun NFS and SMB/CIFS.

Econets are now mainly operated by retrocomputing enthusiasts. Original hardware is becoming harder and harder to find, with auction sites such as eBay being popular for acquiring Econet hardware such as bridges and FileStores. The 68B54 chip used for communicating with the network is no longer manufactured, though kits for the Model B and Master series are available online.

Support for the Econet protocol has been dropped from the Linux kernel at version 3.5 in 2012.

See also

• List of device bandwidths

External links

• The Econet Enthusiasts Area
• Chris' Acorns