Uploaded May 2024 | Updated September 2026, 2 weeks ago
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: youtu.be/lCPZAYvk940
Part 3: youtu.be/_IrxvDE6Fyo
Part 4: youtu.be/Ve1SuuRkx_o
-- Links
My Github Repo (with ROM dumps and images)
github.com/misterblack1/plexus-p20
Plexus P/20 Brochure:
bitsavers.org/pdf/plexus/brochures/Plexus_P15_P20_Brochure_1985.pdf
Plexus Unix:
bitsavers.org/pdf/plexus/brochures/Plexus_SYS_5.2_Brochure_1985.pdf
MFM emulator:
pdp8online.com/mfm/mfm_old.shtml
Fujitsu Hard Drive Brochure:
archive.org/details/bitsavers_fujitsubro1984_2565589
Omti 5200 Manual:
oldcomputers.dyndns.org/public/pub/roms/omti-5400/omti_5000_series_reference_aug85.pdf
Adrian's Digital Basement Merch store:
my-store-c82bd2-2.creator-spring.com
Adrian's Digital Basement ][ (Second Channel)
youtube.com/channel/UCbtwi4wK1YXd9AyV_4UcE6g
Support the channel on Patreon:
patreon.com/adriansdigitalbasement
My GitHub repository:
github.com/misterblack1?tab=repositories
-- Tools
Deoxit D5:
amzn.to/2VvOKy1
store.caig.com/s.nl/it.A/id.1602/.f
O-Ring Pick Set: (I use these to lift chips off boards)
amzn.to/3a9x54J
Elenco Electronics LP-560 Logic Probe:
amzn.to/2VrT5lW
Hakko FR301 Desoldering Iron:
amzn.to/2ye6xC0
Rigol DS1054Z Four Channel Oscilloscope:
rigolna.com/products/digital-oscilloscopes/1000z
Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier:
amzn.to/3adRbuy
TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)
amzn.to/2wG4tlP
aliexpress.com/item/33000308958.html
TS100 Soldering Iron:
amzn.to/2K36dJ5
ebay.com/itm/TS100-65W-MINI-Digital-OLED-Programmable-Soldering-Iron-Anti-static-Structure/113382669853
EEVBlog 121GW Multimeter:
eevblog.com/product/121gw
DSLogic Basic Logic Analyzer:
amzn.to/2RDSDQw
ebay.com/itm/USB-Logic-DSLogic-Basic-Analyzer-16Ch-100MHz-4Ch-400MHz-Xilinx-Spartan-6-FPGA/202543965672
Magnetic Screw Holder:
amzn.to/3b8LOhG
harborfreight.com/4-inch-magnetic-parts-tray-90566.html
Universal ZIP sockets: (clones, used on my ZIF-64 test machine)
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)
retrotink.com
Plato (Clone) Side Cutters: (order five)
ebay.com/itm/1-2-5-10PCS-Micro-Scissor-125mm-PLATO-170-Electronics-Cutter-Side-Cutting-Pliers/163458746184
Heat Sinks:
aliexpress.com/item/32537183709.html
Little squeezy bottles: (available elsewhere too)
amzn.to/3b8LOOI
--- Instructional videos
My video on damage-free chip removal:
youtube.com/watch?v=XQVjwPsVFd8
--- Music
Intro music and other tracks by:
Nathan Divino
@itsnathandivino
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: youtu.be/lCPZAYvk940
Part 3: youtu.be/_IrxvDE6Fyo
Part 4: youtu.be/Ve1SuuRkx_o
-- Links
My Github Repo (with ROM dumps and images)
github.com/misterblack1/plexus-p20
Plexus P/20 Brochure:
bitsavers.org/pdf/plexus/brochures/Plexus_P15_P20_Brochure_1985.pdf
Plexus Unix:
bitsavers.org/pdf/plexus/brochures/Plexus_SYS_5.2_Brochure_1985.pdf
MFM emulator:
pdp8online.com/mfm/mfm_old.shtml
Fujitsu Hard Drive Brochure:
archive.org/details/bitsavers_fujitsubro1984_2565589
Omti 5200 Manual:
oldcomputers.dyndns.org/public/pub/roms/omti-5400/omti_5000_series_reference_aug85.pdf
Adrian's Digital Basement Merch store:
my-store-c82bd2-2.creator-spring.com
Adrian's Digital Basement ][ (Second Channel)
youtube.com/channel/UCbtwi4wK1YXd9AyV_4UcE6g
Support the channel on Patreon:
patreon.com/adriansdigitalbasement
My GitHub repository:
github.com/misterblack1?tab=repositories
-- Tools
Deoxit D5:
amzn.to/2VvOKy1
store.caig.com/s.nl/it.A/id.1602/.f
O-Ring Pick Set: (I use these to lift chips off boards)
amzn.to/3a9x54J
Elenco Electronics LP-560 Logic Probe:
amzn.to/2VrT5lW
Hakko FR301 Desoldering Iron:
amzn.to/2ye6xC0
Rigol DS1054Z Four Channel Oscilloscope:
rigolna.com/products/digital-oscilloscopes/1000z
Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier:
amzn.to/3adRbuy
TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)
amzn.to/2wG4tlP
aliexpress.com/item/33000308958.html
TS100 Soldering Iron:
amzn.to/2K36dJ5
ebay.com/itm/TS100-65W-MINI-Digital-OLED-Programmable-Soldering-Iron-Anti-static-Structure/113382669853
EEVBlog 121GW Multimeter:
eevblog.com/product/121gw
DSLogic Basic Logic Analyzer:
amzn.to/2RDSDQw
ebay.com/itm/USB-Logic-DSLogic-Basic-Analyzer-16Ch-100MHz-4Ch-400MHz-Xilinx-Spartan-6-FPGA/202543965672
Magnetic Screw Holder:
amzn.to/3b8LOhG
harborfreight.com/4-inch-magnetic-parts-tray-90566.html
Universal ZIP sockets: (clones, used on my ZIF-64 test machine)
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)
retrotink.com
Plato (Clone) Side Cutters: (order five)
ebay.com/itm/1-2-5-10PCS-Micro-Scissor-125mm-PLATO-170-Electronics-Cutter-Side-Cutting-Pliers/163458746184
Heat Sinks:
aliexpress.com/item/32537183709.html
Little squeezy bottles: (available elsewhere too)
amzn.to/3b8LOOI
--- Instructional videos
My video on damage-free chip removal:
youtube.com/watch?v=XQVjwPsVFd8
--- Music
Intro music and other tracks by:
Nathan Divino
@itsnathandivino
