RM Nimbus

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RM Nimbus
Developer Research Machines Limited
Type Personal computer
Release date 1985
Media 3.5-inch floppy disk
Operating system MS-DOS
CPU 80186 at 10 MHz
Memory 192 KB upgradeable to maximum 1024 KB
Connectivity Microsoft Networks (optional)
Website RM Education

The RM Nimbus system was a proprietary computer system developed by the UK company Research Machines Limited, aimed mainly at the UK schools market. It could be as simple as a single stand-alone workstation, or a complex network, or multiple machines all running their own proprietary software - or modified software from other software houses.

Nimbus Network[edit]

A normal Nimbus network was a collection of workstations, and one or more servers. The original system was developed with the Nimbus AX as the server and the Nimbus PC-186 as the workstation, or print server. Later on the VX series was introduced as a replacement for the AX server, and the PC-286 and PC-386 workstations were produced. AX or VX machines could also operate as workstations if required, for example, if an AX server had been replaced by a VX, the AX could find general use as a workstation.

The server would act as both a network boot server, file and print server. Any type of Nimbus machine (usually a PC-186) could in addition be added to act as a dedicated print server, however all print jobs were still routed via the main server and then the jobs copied as files from the server to the print server over the network. This in theory prevented the server from having to copy data to the parallel port and freeing up CPU cycles for other tasks, however it also put more data onto the network bus. However, this function was useful if two printers were needed (usually one color and one black and white), as the original AX/VX machines only had one parallel port, and serial printing was rapidly become non standard.

The network was connected via BNC cable with T-pieces and ran on Zilog's Z-Net system. It allowed up to 127 workstations to be connected and booted directly from the network server. A complex user log-on system - with significant vulnerabilities - was implemented allowing multiple user groups and for each group to be assigned a different menu structure in the original user interface, or different Program Managed windows in the later Windows 3.0 interface. For example, in Windows 3.1, the 'File' menu was missing from Program Manager, preventing users from running programs other than what the network administrator intended.

Most workstations were also equipped with a Piconet port but this rapidly became redundant due to the higher speeds with Z-net.

Nimbus PC-186[edit]

The RM Nimbus PC-186 was a 16-bit microcomputer produced by Research Machines Limited in Oxford, England, during the mid-1980s.[1]

It was developed as the original workstation for the Nimbus network system, and ran a modified version of MS-DOS, and in its native form was not 100% IBM PC compatible, requiring the use of the 'SETMODE.com' application to switch between RM mode and PC code. It was replaced towards the end of the life of the Nimbus system with the PC-286 and PC-386 workstations, both of which were 100% PC compatible.

In most nimbus systems the 186 workstations were disk-less, with some having a single floppy drive. Stand alone workstations were also made - most with either twin floppy drives, or a 20Mbyte hard drive and single floppy drive.

I/O Connectors[edit]

Mouse - 9 pin D-Sub connector with pins wired in a different configuration to a standard 9-pin serial port
Keyboard - Earlier models- Standard XT keyboard port, Later models -PS/2 keyboard port
Video - 5 pin DIN plug with TTL RGB output compatible with BBC micro monitor connectors - modified CGA output
Parallel - Optional via expansion card - usually with BBC micro 'user port' alongside- both with ribbon pin connectors
Network -BNC connector - Zilog Z-NET, Ethernet expansion cards were available for later models - both allowed network boot
Power - Standard IEC connector in and out for monitor supply

RM AX/VX Servers[edit]

Both of these systems were used a servers for the Nimbus Network, but could also be used as standalone workstations. They employed either EGA or VGA graphics cards, and were equipped with an ESDI interface for a hard drive, as well as a 3 1/2" floppy drive.

They were listed as 100% PC compatible, but only when SETMODE was used to select PC mode.

By default they were equipped with a Z-Net interface card, but a second Ethernet card could be added alongside to allow both network interfaces to be used simultaneously, however, the two network interfaces were not able to be bridged.

Expansion cards could be added to standard 8-bit and 16-bit ISA sockets, which were both on the motherboard, and on an attached expansion board which was supplied as standard

PC-286, PC-386 and PC-486[edit]

RM subsequently released Intel 286, 386 and 486 versions. The 286 version, and early 386 versions used a similar case design to the 186. The later 386 and 486 versions featured a redesigned case, with the option of a CD-ROM drive, and typically ran at 25MHz.