Photos of a Daybreak

[Paolo Amoroso]

A Mastodon user posted some photos of his Daybreak workstation running the memory tests.

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Paolo Amoroso | Blog | Mastodon

[Ellie Young]

Wow, cool! How does the memory test work?

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[Paolo Amoroso]

I think the test program is writing data patterns to video memory so that the operator can spot anomalies by visually examining the screen. Since the memory layout is known the location of the anomalies can help pinpoint the faulty chips or memory blocks. In general memory test programs write data patterns in memory and read them back to compare the retrieved data with what expected.

Early home and personal computers had such tight resource constraints (e.g. the Sinclair ZX81 with 1 KiB of RAM) that some programs stored application data in video memory, resulting in visually interesting patterns appearing on the screen. If I recall correctly some games or programs even took advantage of this to generate visual effects.

[Nick Briggs]

Yes, it's doing the pattern testing to identify down to the board/chip level if there's a failure (which could be an addressing failure, or content failure).

You might look at the Google results for [patterns used in diagnostic computer memory tests]. We didn't have the modern stress tests like the one for Row Hammer then.

The video memory is just a few blocks of the main memory, so a side-effect of doing the pattern testing is that you see part of it on the display.

See RAP 14 Memory Chip Isolation in the 6085 service manual -- https://www.bitsavers.org/pdf/xerox/6085/service/700P05710_6085_PCS_Service_Manual_Oct88.pdf for the info that the field engineer would use to locate which board/chip had failed.

--- Nick

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[Paolo Amoroso]

A cameo of a Daybreak running ViewPoint at Vintage Computer Festival Pacific Northwest 2026.

[Larry Masinter]

The Alto memory check. took advantage of the network so that if your Alto had a bad chip, the failing chip would be reported.: Upon detecting a bad chip, the Alto would automatically send an Ethernet message to a server identifying the specific machine, board slot, and the exact row/column of the failed memory chip.

I don't think this aspect of idle program was carried over to the D-machines.  

But screen burn-in was a risk, which gave rise to many idle hacks ... i made a IDLEDEMO that loads them all and then chooses at random -- try (FILESLOAD IDLEDEMO) then call (IDLE) or choose Idle on the background menu. It will pick one at random.

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https://LarryMasinter.net  https://interlisp.org

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[Arun Welch]

Funny story about this. One of the files loaded by IDLEDEMO is IDLEHAX, which we had loaded as part of our standard sysout since grad students couldn’t be trusted to turn off their screens, set to pick one of the functions at random. The early version of IDLEHAX didn’t include the Melt function, but it was added along the way. One day shortly after the new version was installed one of the grad students came to my office in an absolute panic thinking his workstation had crashed in a bad way and he hadn’t saved his state for a couple of hours.

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