tl;dr: Non-spec DisplayPort cables were feeding back power from the monitor to the video card, causing my computer to reboot during POST. Buy this cable. //

When I got down on the floor to look inside the case, I saw something moving.

The case fan was spinning.

The freaking case fan was spinning. And I was holding the unplugged power cable in my hand. How is this even possible?!

I unplugged all of the PSU cords from my motherboard, and things shut down. The GPU light turned off, and the fan died.

The next day, I returned to Google, and for the hell of it, searched “computer is on even when unplugged.” I know, it sounds ridiculous, but it lead me to the answer I had been looking for (in addition to a funny meme of The Pope casting holy water for someone with a similar issue).

I scrolled, and scrolled, pages and pages and URL after URL of articles on something called The DisplayPort Pin 20 problem started showing up. It felt so funny to search for months with no solution and then to almost be assaulted by the number of posts on the same issue I was having.

It turns out that cable manufacturers who don’t adhere directly to the official DisplayPort spec end up connecting the 20th pin in the cable on both sides. That pin, carries – you guessed it – power!

This issue was serious. Enough power had been backflowing from my monitors into my GPU to run my case fans when the system was off.

The venerable PDP-11 minicomputer is still spry to this day, powering GE nuclear power-plant robots - and will do so for another 37 years.

That's right: PDP-11 assembler coders are hard to find, but the nuclear industry is planning on keeping the 16-bit machines ticking over until 2050 – long enough for a couple of generations of programmers to come and go.

Now that you've cleaned up the coffee spills and finished laughing, take a look here, at Vintage Computer forums, where GE's Chris Issel has resorted to seek assembly programmers for the 1970s tech.

Wednesday 19th June 2013 08:28 GMT
John Smith 19Gold badge
Coat
PDP 11 odds and ends.
The PDP 11 (like the PARC Alto) had a main processor built from standard 4 bit TTL "ALU" parts and their companion "register file." So 2nd, 3rd,4th sourced. I'm not sure how many mfg still list them on their available list in the old standard 0.1" pin spacing.

El Reg ran a story that Chorus (formerly British Steel) ran them for controlling all sorts of bits of their rolling mills but I can't recall if they are

I think the core role for this task is the refueling robots for the CANDU reactors. CANDU allows "on load" refuelling. The robots work in pairs locked onto each end of the pressurized pipes that carry the fuel and heavy water coolant/moderator. They then pressurize their internal storage areas, open the ends and one pushes new fuel bundles in while the other stores the old ones, before sealing the ends. However CANDU have been working on new designs with different fuel mixes (CANDU's special sauce (C Lewis Page) is that it's run with unenriched Uranium, which is much cheaper and does not need a bomb making enrichment facility) and new fuel bundle geometries, so time for a software upgrade.

And 128 users on a PDP 11/70. Certain customers ran bespoke OSes in the early 90s that could get 300+ when VMS could only support about less than 20 on the same spec.

Note for embedded use this is likely to be RSX rather than VMS, which also hosted the ICI developed RTL/2, which was partly what hosted the BBC CEEFAX service for decades.

Yes, it's an anorak.. //

Wednesday 19th June 2013 18:20 GMT
Jamie JonesSilver badge
Thumb Up
Who's laughing?
I feel much better knowing this.

What is the alternative? Buggy software written by the "'Have you tried switching it off and on again" generation?

RSX11M - Dave Cutler
Anyone who read the RSX11M sources (driver writers especially) realised that Dave Cutler was a very very good programmer long before he worked on VMS and later Windows NT. He managed to get a multiuser protected general purpose operating system to work with a minimum memory footprint of under 32kbytes on machines with about the same CPU power as the chip on a credit card. (A 96kByte PDP 11/40 (1/3 mip) with 2 RK05 disks (2.4Mbyte each) could support 2 concurrent programmers - a PDP 11/70 (1 mip) with 1Mbyte and 2 RM03 disk packs (65Mbyte each) could support 10 or more.) During the many years that the CEGB used PDP-11 computers with RSX11M, I did not hear of a single OS failure that was not caused by a hardware fault - I wish that current systems were as good. //

Wednesday 19th June 2013 15:09 GMT
annodomini2
Reply Icon
FAIL
Re: there are alternatives
They would never redesign the system, if the system has issues, they are known and fixes are well known.

Changing the system design introduces potential risks and unknowns into the system.

It's not about Zero failure, it's about safe and predictable failure. //

Wednesday 19th June 2013 07:53 GMT
Bob Dunlop
Hey I was taught assembler programming using a pdp11 .

After it's nice clean structure, the mess that was 8086 code came as quite a shock.

Wednesday 19th June 2013 20:24 GMT
bscottm
Reply Icon
Re: It just costs money
It's not the GHz clock cycle that is the problem. It's the smaller feature size of the transistors that increases the single event upset (SEU) rate. Yes, the two are inter-related, but one could conceivably build multi-core, chip symmetric multiprocessors based on the PDP-11 at today's feature sizes and not have GHz clock cycle times (and still end up with significant SEU rates.)

A couple of years ago, a NASA/JPL scientist pointed out that the alpha particles (helium nuclei) from lead solder were causing interesting issues with current x86_64 I/O pins -- radiation issues on commodity hardware.

The VGA default palette in the 256 colour mode (Mode 13h) first has 16 color entries from CGA (which is also same as default 16-color EGA palette and the only palette for 320x200 EGA mode)

Next 16 color entries are 16 shades of gray.

And the next 216 color entries has been already mentioned; they are sets of 24 hues, in 3 different saturation values, and in 3 different brightness values. 24 × 3 × 3 = 216.

The final 8 colour entries are black, or maybe left undefined so BIOS does not overwrite them when changing modes.

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• Motherboard Compatibility Micro ATX
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• Item Weight 10.16 Pounds
• Item Dimensions LxWxH 15.35 x 8.07 x 14.96 inches
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• Mini-Tower chassis for motherboard supports Supermicro size Mini-ITX 6.75-inch x 6.75-inch
• Storage Chassis: 4x 3.5-inch hot-swap SAS/SATA, 2x 2.5-inch fixed drive bay