What is this rare multi-user UNIX workstation? (Plexus P/20)

What we have on the bench is a Plexus P/20 dual processor multi-user UNIX computer from 1985. This was likely designed for office user and support 8 concurrent users in this configuration, with up to 16 possible with the use of an extra I/O processor card. This machine doesn't seem to be documented anywhere other than a simple brochure (link below) so let's see if we can unravel some of the mysteries of this machine.

Part 1: This part Part 2: Coming soon!

-- Links

My Github Repo (with ROM dumps and images) https://github.com/misterblack1/plexus-p20

Plexus P/20 Brochure: http://www.bitsavers.org/pdf/plexus/brochures/Plexus_P15_P20_Brochure_1985.pdf

Plexus Unix: http://www.bitsavers.org/pdf/plexus/brochures/Plexus_SYS_5.2_Brochure_1985.pdf

MFM emulator: https://www.pdp8online.com/mfm/mfm_old.shtml

Fujitsu Hard Drive Brochure: https://archive.org/details/bitsavers_fujitsubro1984_2565589

Omti 5200 Manual: https://oldcomputers.dyndns.org/public/pub/roms/omti-5400/omti_5000_series_reference_aug85.pdf

Adrian's Digital Basement Merch store: https://my-store-c82bd2-2.creator-spring.com/

Adrian's Digital Basement ][ (Second Channel) https://www.youtube.com/channel/UCbtwi4wK1YXd9AyV_4UcE6g

Support the channel on Patreon: https://www.patreon.com/adriansdigitalbasement

My GitHub repository: https://github.com/misterblack1?tab=repositories

-- Tools

Deoxit D5: https://amzn.to/2VvOKy1 http://store.caig.com/s.nl/it.A/id.1602/.f

O-Ring Pick Set: (I use these to lift chips off boards) https://amzn.to/3a9x54J

Elenco Electronics LP-560 Logic Probe: https://amzn.to/2VrT5lW

Hakko FR301 Desoldering Iron: https://amzn.to/2ye6xC0

Rigol DS1054Z Four Channel Oscilloscope: https://www.rigolna.com/products/digital-oscilloscopes/1000z/

Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier: https://amzn.to/3adRbuy

TL866II Plus Chip Tester and EPROM programmer: (The MiniPro) https://amzn.to/2wG4tlP https://www.aliexpress.com/item/33000308958.html

TS100 Soldering Iron: https://amzn.to/2K36dJ5 https://www.ebay.com/itm/TS100-65W-MINI-Digital-OLED-Programmable-Soldering-Iron-Anti-static-Structure/113382669853

EEVBlog 121GW Multimeter: https://www.eevblog.com/product/121gw/

DSLogic Basic Logic Analyzer: https://amzn.to/2RDSDQw https://www.ebay.com/itm/USB-Logic-DSLogic-Basic-Analyzer-16Ch-100MHz-4Ch-400MHz-Xilinx-Spartan-6-FPGA/202543965672

Magnetic Screw Holder: https://amzn.to/3b8LOhG https://www.harborfreight.com/4-inch-magnetic-parts-tray-90566.html

Universal ZIP sockets: (clones, used on my ZIF-64 test machine) https://www.ebay.com/itm/14-16-18-20-24-28-32-40-pin-IC-Test-Universal-ZIF-Socket-Fs/303206721971

RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI) http://www.retrotink.com/

Plato (Clone) Side Cutters: (order five) https://www.ebay.com/itm/1-2-5-10PCS-Micro-Scissor-125mm-PLATO-170-Electronics-Cutter-Side-Cutting-Pliers/163458746184

Heat Sinks: https://www.aliexpress.com/item/32537183709.html

Little squeezy bottles: (available elsewhere too) https://amzn.to/3b8LOOI

--- Instructional videos

My video on damage-free chip removal: https://www.youtube.com/watch?v=XQVjwPsVFd8

--- Music

Intro music and other tracks by: Nathan Divino @itsnathandivino ... https://www.youtube.com/watch?v=iltZYXg5hZw