LaurieWired Profile picture
Aug 15 5 tweets 3 min read Read on X
lp0 is a Linux error code that means “printer on fire.”

It’s not a joke. In the 50s, computerized printing was an experimental field.

At LLNL (yes, the nuclear testing site), cathode ray tubes created a xerographic printer.

...it would occasionally catch fire. Image
Image
State-of-the art at the time, the printer was modified with external fusing ovens hit a whopping…

1 page per second!

In the event of a stall, fresh paper would continuously shoot into the oven, causing aggressive combustion. Image
As tech later advanced to drum machines, the fire “problem” didn’t go away.

High speed rotary drums could cause enough friction during a jam to self-combust.

Even minor hangups needed immediate intervention. Image
In the 80s, Xerox created the first prototype laser printer.

Apparently learning nothing from lessons of the past, paper had to pass directly over a glowing wire.

If a jam occurred *anywhere* in the system, the sheet in the fuser would immediately catch fire.

The prototype UNIX driver reported every jam as “on fire” to motivate the technician to take an immediate look.

lp0 still exists to this day in the Linux source code!

Go and search the git tree for “on fire”, you’ll find it!Image
Image
correction, the full error code is “lp%d on fire”, where lp%d refers to the printer itself

my brain is tired cut me some slack Image

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More from @lauriewired

Nov 1
A Spooky Unix story for Halloween.

A new programmer accidentally ran “rm -rf *” as root, on one of the main computers at UoM.

He stopped halfway, but /bin, /etc, /dev, and /lib were gone.

What followed was one of the most insane live recoveries in computer history: Image
Image
A single Emacs session was still open, with a root shell.

Many student’s PhD thesis work was on the box. Every basic tool, ls, cd, mkdir, etc was already wiped.

The last tape backup was a week ago. Any downtime was unthinkable. Image
Image
*Assuming* you could copy or recover any tools, they needed a place to put them.

How do you rename /tmp to /etc…without mv?

Don’t forget; you can’t even compile code.

Remember that single Emacs session? Yeah, time to break out some raw VAX assembly. Image
Read 4 tweets
Oct 17
You’re (probably) measuring application performance wrong.

Humans have a strong bias for throughput.

"I can handle X requests per second."

Real capacity engineers use response-time curves. Image
Image
It all comes down to queueing theory.

Unfortunately, computers don’t degrade gracefully under load.

70% CPU is smooth sailing. 95% is a nightmare.

Programmers (incorrectly) focus on the absolute value, when really they should be looking at the derivative. Image
Image
Highways are the perfect real life example of this.

Traffic engineers study flow density, not overall vehicle counts.

A road handling 10,000 cars per hour (throughput) means nothing if the average speed drops to 5mph (response time).

Computers are the same. Image
Image
Read 4 tweets
Oct 14
GPU computing before CUDA was *weird*.

Memory primitives were graphics shaped, not computer science shaped.

Want to do math on an array? Store it as an RGBA texture.

Fragment Shader for processing. *Paint* the result in a big rectangle. Image
Image
As you hit the more theoretical sides of Computer Science, you start to realize almost *anything* can produce useful compute.

You just have to get creative with how it’s stored.

The math might be stored in a weird box, but the representation is still valid. Image
BrookGPU (Stanford) is widely considered the birth of a pre-CUDA GPGPU framework.

Virtualizing CPU-style primitives; it hid a lot of graphical “weirdness”.

By extending C with stream, kernel, and reduction constructs, GPUs started to act more like a co-processor. Image
Read 4 tweets
Oct 13
Colleges do a terrible job of teaching C++.

It’s not “C with Classes”. Injected into curriculums as a demonstration of early CS concepts, it leaves many with a sour taste.

Students later immediately fall in love with the first language that *doesn’t* feel that way. Image
Admittedly, professors are in a tough spot.

To teach the concept, you fundamentally have to constrain the scope of the language. Many schools choose C++ out of practicality.

Controversially, I think toy languages that *aren't* industry standards are better suited for this. Image
Imagine learning the fundamentals of carpentry, but for teaching reasons, an otherwise reputable brand is artificially constrained to hand tools.

Of course, the moment a student jumps into the real world, and experiences their first power tool, it will blow their mind! Image
Image
Read 5 tweets
Oct 3
DDR5 is unstable garbage.

Max out your memory channels? Flaky.
Temperature a bit too hot? Silent Throttle with no logs.
Too “Dense” of a stick? Good luck training.

Last gen was rock solid by comparison. Here's what happened. Image
Image
More than ever, manufacturers have been pushing memory to the absolute limits.

JEDEC, the standards committee, is pretty conservative.

Yet the moment DDR5 launched, everyone threw JEDEC out the window.

Intel + AMD's memory controllers were *not* ready to handle it. Image
DDR5-4800 was the baseline.

Day one kits were pushing 6000+. Today, even 8000+.

On-die error correction is masking chips that would have been binned as trash in the DDR4 era.

The gap between JEDEC spec and retail has never been wider. Image
Read 4 tweets
Oct 2
Virtual Machines render fonts. It’s kind of insane.

TrueType has its own instruction set, memory stack, and function calls.

You can debug it like assembly. It’s also exploitable: Image
Image
Anytime you can run code (albeit very limited code), someone will take advantage of it.

TrueType (TT) is unfortunately famous for many Windows Kernel zero days.

TT is memory bound, therefore not Turing-complete…but you can still do crazy things with it. Image
Fontemon is a fun one, a pokemon-style game packaged as a TTF.

llama.ttf is even more insane. A 60MB font that runs a 15M parameter llama model to generate stories.

Seemingly normal at first, when you use excessive exclamation points it starts to generate text!
Read 4 tweets

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