Econet

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.^[1]

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.^[2]

Machine Type numbers ^[3]

Machine type numbers are as follows:

&0000	Reserved
&0001	Acorn BBC Micro Computer (OS 1 or OS 2)
&0002	Acorn Atom
&0003	Acorn System 3 or System 4
&0004	Acorn System 5
&0005	Acorn Master 128 (OS 3)
&0006	Acorn Electron (OS 0)
&0007	Acorn Archimedes (OS 6)
&0008	Reserved for Acorn
&0009	Acorn Communicator
&000A	Acorn Master 128 Compact Econet Terminal
&000B	Acorn Filestore
&000C	Acorn Master 128 Compact (OS 5)
&000D	Acorn Ecolink card for Personal Computers
&000E	Acorn Unix Workstation
&000F to &FFF9	Reserved
&FFFA	SCSI Interface
&FFFB	SJ Research IBM PC Econet interface
&FFFC	Nascom 2
&FFFD	Research Machines 480Z
&FFFE	SJ Research File Server
&FFFF	Z80 CP/M

This Isolated Excerpt table comes from a section describing the Econet_MachinePeek command, used by some software to determine if a machine is still present on the network. Manual § also includes an assembly language program to report s/w ver. and release №'s.

Is given here to to illustrate the wider range of officially connected systems. It is useful to note that Acorn produced a range of different multiprocessor systems that could support non-Acorn Operating systems often in parallel like CP/M, DR-DOS, Unix along with both implementations of the then current MS-Windows and X Window System sold too.^[4] The other non acorn systems look like common computers that may be in British schools and made to work with suitable network interfaces. Research Machines started making BBC clones for a share of the education market before developing partly compatible IBM-PC clones due to customer demand for more power in the gap between the Early BBC's and the leap to Risc CPU's in 1987's Archimedes new complete reference model {early Risc cpu's connected via TUBE to be 2nd processors for slower BBC host systems}.^[5]

The date of publication means that this was an early edition therefore corrections and extensions are very possible. An updated version of the whole manual as well as older reference material can be bought or discussed from the current development teams for the RISC-OS systems and some manuals are still available for inter-library loans sourced in the UK.^[6]

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.^[7]

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. A 'four way handshake' consists of four frames:-

1. A "scout" that contains four single byte numbers of destination station number (computer, server or other end node)
2. network number of destination station source's station number
3. source's network number with a port byte
4. a flag byte.

The receiver replies with the scout ack that only contains the first four bytes of the scout.

The source then sends the data frame consisting of the common first four bytes of the scout and then all the data.

Finally the destination concludes with the fourth final acknowledge frame which is identical to the scout acknowledge frame.^[8]

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.

In addition to the basic services a number of solutions could be bought or were otherwise also available that made Teletext and modem servers using a hosting computer for the station's data preparation, device-driving/control (modem or teletext receiver) and Network data handling.^[9] The limiting factor was what sysops wanted the whole LAN to use and had fitted to the LAN which wasn't often too much more than the fileserver and the printers.

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.^[10]

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.^[11]

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 , 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

Econet was developed in a time (late 1970s to early 1980s) when standalone computers were common both domestically as well as in business environments. Networks were beginning to slowly spread, often seen as exotic campus or institution-wide projects. At that time, networks often use custom designs with private protocols.

Econet was a good "off-the-shelf" solution for Acorn Equipment of that time. While computing speeds and data rate demands prompted faster versions of common protocols like Ethernet, and design new ones like FDDI. Acorn systems developed in giant leaps after a relatively long period. This meant new machines needed to co-operate with more limited machines and legacy servers in the same time period. The fact that Econet was still a single line broadcast system rather than being evolved into point-to-point hub based system (such as Ethernet over twisted pair), made it tougher to reliably accelerate data rates while maintaining compatibility with all old circuity. So rather than do to Econet as was done to Ethernet to move it higher and higher multi-speed support and into Wi-Fi, Acorn seemed to have decided to migrate in stages to supporting a wider number of fast networking systems.

It is worth seeing the wider context in Acorn the marketing was trying to make models that appealed to higher education (complete with Unix) as well as an improved choice for small businesses. Domestic users were buying not just their first computer but maybe their third, and increasingly different members of the household owned their own computers creating an increasingly heterogeneous computing environment. Acorn machine began to handle foreign formats of discs and archive as well as media files.

Econet hardware implementations started to disappear from new Acorn machines around 1993 with the RiscPC machines. Previous machines could accept Econet modules as add-ons via an adaptation of the connector used in BBC Master computers. The RiscPC range used a new network slot connector that would not accept the old modules. Podules, a name for daughtercard-like cards, could still be fitted, although a later Econet module was manufactured for this new connector along with cards supporting a few sockets on one card for multi-homing and compatibility.

Econet software 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 Network File System (NFS) and SMB/CIFS.

Econets are now mainly operated by retrocomputing enthusiasts. Original hardware is 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 was dropped from the Linux kernel at version 3.5 in 2012.^[12]

See also

• List of device bandwidths

External links

• The Econet Enthusiasts Area
• Chris' Acorns

References