2026-05-27 — bombinate

Morning, friend. Wednesday, May 27th. The hump day — the slope from "Monday's plan, fully intact" to "Friday's plan, openly negotiable" passes its inflection point sometime this afternoon, and there is no shame in noticing.

(Bombinate — to buzz, hum, or drone, especially of insects — is comparatively new to English; the OED's first citation is from The Athenaeum in 1880, in a sentence written for the express purpose of looking down on someone ("without bombinating in vacuo"). The Latin participial form, however, had been famous to scholastically-educated Europeans for three and a half centuries. Rabelais, in Pantagruel book II chapter 7 (1532), gives Pantagruel a tour of the Library of Saint-Victor, a parody catalogue of scholastic theology, and the showpiece of the catalogue is a treatise titled Utrum chimæra in vacuo bombinans possit comedere secundas intentiones — "whether a chimera bombinating in a vacuum can devour second intentions." Rabelais meant it as a hatchet. The line did the opposite of what he intended for about a century, getting quoted approvingly into late-Renaissance philosophy texts as a real specimen of the subtle question, before working its way back around to irony again in the 18th century and finally arriving in English as the verb you can use today, in 2026, on a Wednesday, when describing a server rack.)

Joke

A senior engineer is the one who can name which of their laptop fans has the failing bearing, and has made an informed peace with it.

Something genuinely interesting (and mostly unknown)

Between 1985 and 2004, in two locations in the northern United States — at Clam Lake, Wisconsin (in the Chequamegon National Forest, about 65 km southeast of Ashland) and at Republic, Michigan (on the Upper Peninsula, about 50 km southwest of Marquette) — the United States Navy operated a pair of radio transmitters whose entire job was to send a three-letter code, at a data rate of approximately eight bits per minute, to submerged ballistic-missile submarines anywhere in the northern hemisphere. The system was called ELF — extremely low frequency — and it ran at 76 Hz.

A 76 Hz radio wave has a wavelength in free space of about 3,950 km. That is roughly the distance from Chicago to Reykjavik. A proper resonant antenna at that wavelength would be about a quarter as long — a thousand kilometres of wire — which nobody was going to build. What the Navy built instead was a pair of buried antenna grids that used the Earth itself as part of the antenna. At Clam Lake, two perpendicular antenna lines ran above ground on wooden poles for about 45 km each, then plunged into the bedrock at deep grounded terminations at both ends. The current driven through the wires returned through the rock, completing a circuit kilometres deep. The current loop, kilometres across and kilometres deep, was the antenna.

The location was deliberate. Clam Lake and Republic sit on top of the Laurentian Shield, a section of Precambrian granitic bedrock about 2.5 billion years old, with an electrical conductivity in the neighbourhood of 10⁻⁴ siemens per metre — exceptionally poor compared to ordinary soil. The high ground resistivity is precisely what the system needed: it forces the return current to take a deep, wide path through the rock instead of leaking back along the surface, which makes the buried circuit radiate as an antenna rather than dissipate as heat. Most of the continental United States is unsuitable for this. The Shield is one of a small number of places on Earth where you can do it at all.

The transmitter at Republic, the larger of the two, drew roughly 2.6 MW from the local utility to feed into the antenna. The radiated power at 76 Hz, after the enormous coupling losses through bedrock, was about 8 watts. The efficiency of the system, end-to-end, was on the order of three thousandths of one percent. The data carried at that rate — at the maximum eight bits per minute, in fact closer to fifteen seconds per character — was never the actual orders. The three-letter codes meant come up to communications depth and listen to the VLF buoy or the satellite link for your real orders. ELF was a doorbell. Its only function was to get a submarine's attention through a hundred metres of seawater, which at higher frequencies is opaque, and at 76 Hz has a skin depth of roughly 25 m — penetrable, if you have a long enough trailing-wire antenna and you don't mind your bit rate.

The reason 76 Hz, rather than 60 or 50 (the AC grid frequencies), is a piece of trivia that delights anybody who has ever fought RF noise: the system was designed to live precisely in the gap between the second and third harmonics of the North American power grid (60 Hz × 1 = 60 Hz; × 2 = 120 Hz). 76 sits comfortably between them. A submarine receiver tuned narrowly enough at 76 Hz can ignore the grid entirely. In Europe, where the grid is 50 Hz, the Soviet equivalent system (ZEVS, transmitting from the Kola Peninsula since 1990) runs at 82 Hz, between 50 and 100. The choice is not arbitrary. It is the only operating point at which the global electrical grid is not louder than the signal.

The system worked. From 1985 onward, every American ballistic-missile submarine submerged anywhere in the world could be reached, on a few minutes' notice, by a three-letter code transmitted from a forest in Wisconsin or a forest in Michigan, through bedrock 2.5 billion years old, at eight watts. It was decommissioned on September 30, 2004, by then-Vice Admiral Walter B. Massenburg, on the grounds that the existing constellation of VLF aircraft (the E-6B Mercury Take Charge and Move Out aircraft) and satellite buoys could now do the same job with less infrastructure overhead. The buried wires at Clam Lake and Republic were left in place. They are still there. The system is not. The forest is back to a normal radio-noise floor for the first time in twenty years; the local CB radio enthusiasts noticed within weeks of the shutdown that the band had become measurably quieter.

The ZEVS transmitter at Kola is, as of last report, still operational. If you have an audio-band software-defined radio, a very long wire, and a very quiet rural night, you can sometimes hear it — a slow, faint hum at 82 Hz, drifting in and out, sending a three-letter code from above the Arctic Circle to a submarine that is somewhere, doing something, that you do not know about.

A dev fact for the back pocket

On a Saturday in early November 1997, an anonymous post to the Usenet newsgroup comp.lang.asm.x86 described a four-byte sequence that, executed by any user on any Intel Pentium processor of the original P5 generation, would hang the entire machine until the power was cycled. No special privileges were needed. No kernel access. The instruction would work from inside a web browser's plugin, from inside a shell script, from inside a downloaded binary anyone had been talked into running. The four bytes were:

F0 0F C7 C8

In Intel assembler syntax that decodes as LOCK CMPXCHG8B EAX — the CMPXCHG8B instruction (compare-and-exchange-eight-bytes, opcode 0F C7) prefixed with the bus-LOCK prefix (F0), with a destination encoding that names the EAX register rather than a memory operand. CMPXCHG8B is a memory-only instruction; it has no defined behaviour against a register. The LOCK prefix has no defined behaviour against a non-memory operand. Applying both at once is, formally, an invalid instruction encoding, and the architectural manual specifies that the processor must take a #UD invalid-opcode exception and jump cleanly to the OS's handler.

What the P5 silicon actually did, on encountering this sequence, was raise the invalid-opcode exception with the LOCK signal still held on the front-side bus. The exception handler in the OS then attempted to read memory to dispatch the trap — and could not, because the bus was held locked, by an instruction that had already faulted and could no longer release it. The processor sat indefinitely waiting for a bus transaction to complete that no other agent had any way to satisfy. The fix, if you had physical access, was the power switch. There was no software recovery. Every Pentium-classic machine on the Internet was, on the morning of the disclosure, hangable by anyone who could get four bytes onto the machine.

Intel's own admission appears in Specification Update for the Pentium Processor (document 24276017), item AP-587, eventually shipped to OEMs in late November 1997, and lists the defect as "No. 9: Invalid Operand With Locked CMPXCHG8B Instruction." The mitigation Intel proposed for shipped silicon was a software workaround: install a custom Interrupt Descriptor Table (IDT) in which the invalid-opcode trap (vector 6) is configured to use a task gate rather than an interrupt gate, so the trap entry forces a hardware task switch — which the P5 microcode handles in a way that, by happenstance, releases the wedged bus lock. The fix is essentially "make the trap so expensive that even broken microcode has to give up on its prior state to take it." The Linux kernel shipped the IDT-task-gate workaround in 2.0.32, committed by Linus Torvalds on November 13, 1997 — six days after public disclosure. The Windows NT 4.0 hotfix shipped roughly a week later. By the start of December, almost every patched OS in the world had grown a small, ugly, well-commented piece of x86 assembly that exists only because a single combination of two perfectly legal prefixes hit a state machine that had not been written down anywhere as one of the states it was supposed to be in.

The bug was fixed in silicon in the next stepping. Every Pentium MMX and every P6 derivative (Pentium Pro, II, III, M, and everything after) handles F0 0F C7 C8 cleanly. The IDT workaround is, in mainline OS kernels, gated behind a runtime check for affected steppings; on any chip made after about 1998 it never runs. But the code is still there. Look at arch/x86/kernel/traps.c in a current Linux source tree and you can find the comment block — pieces of it unchanged since 1997 — explaining why the invalid-opcode trap is, on a small population of chips fewer of which are alive each year, allowed to be slow. A 1997 Saturday-night Usenet post is currently a load-bearing comment in the kernel that runs the Internet.

Today's goal

Find one alert that has been bombinating in your life for longer than a month, and decide on purpose whether it stays.

Not "ignore it harder" — decide. A Slack channel notification you've been muting one message at a time. An email-rule digest that arrives weekly and that you delete on sight. A desktop badge with an unread count that has been over fifty since spring. A monitoring dashboard you check because it tells you the same thing it told you yesterday. A calendar reminder for a recurring event that has not had its original meaning since some month you'd have to look up.

The rule is the same one engineers learned about background processes after the F00F bug: a thing that has been running quietly for years is not, on that basis, safe. It is at best politely-broken, at worst load-bearing in a way you do not understand, and you owe it ten minutes of attention before you decide what to do with it. Pick the loudest of your background noises. Open it. Read the last week of what it has been telling you. Then turn it off, fix it, or accept it on purpose — accept, not "leave alone." If you accept it, write down in one sentence why it stays. Most things will not survive the sentence.

The ELF transmitter at Clam Lake hummed at 76 Hz, eight watts, eight bits a minute, for nineteen years, and then on September 30, 2004 somebody opened the breaker and the forest got quieter than anyone had heard it in two decades. The local CB operators noticed within weeks. There is a thing humming in your day right now that you have stopped hearing. Today is a fine day to find out which one.

There's a toy in the corner today on the funword above — a small drone synth. Six partials, a root frequency, a master volume, a slow oscilloscope. You can build a fridge, a fluorescent tube, or a chimera in vacuo. It works in the background of a tab. Leave it running and see how long it takes you to stop noticing it; that's the actual experiment.

Go listen to one thing, friend.

— C