Xgrid

~ the last words ~

Xgrid came out of a group inside Apple called Advanced Computation, which existed because somebody there in the early 2000s believed universities were about to buy Macs by the rack. Technology Preview 1 went out in January 2004. The shipping version arrived with Mac OS X Server 10.4 Tiger in April 2005, and from then until 10.7 it was simply part of the operating system rather than a product you bought.

The shape of it was three jobs for three kinds of machine. A client submitted the work, and a controller broke it into pieces and tracked who held which one. The agents were ordinary Macs that had agreed to take pieces, and the usual arrangement was that they took them when nobody was sitting at the keyboard. Apple shipped a graphical Xgrid Admin for watching all this, plus a pair of command line tools for people who would rather not watch.

The demos were Mandelbrot sets and 3D rendering, because those divide neatly and look good on a projector. The real use was quieter. MacResearch ran a public grid called OpenMacGrid for scientists who needed cycles. Stanford ran Xgrid@Stanford across campus machines and beyond for biochemistry work. This was the same decade that taught a generation of people the words distributed computing through a screensaver, and Xgrid applied the idea at the scale of one building.

It ended without a sentence written about it. OS X 10.8 Mountain Lion shipped on 25 July 2012 with no Xgrid in it, which also took out Podcast Producer, Apple's recording and publishing system that had been quietly using Xgrid to do its rendering. There was no replacement and no migration path. Anyone on 10.7 kept it until the day they upgraded.

~ the record ~

~ the screensaver model ~

What made Xgrid interesting was the scheduling assumption rather than the compute. Everyone in 2005 knew a lab full of machines was idle most of the day. The hard part was never the arithmetic, it was persuading thirty computers with thirty owners to cooperate without anyone writing cluster code or filing a ticket.

Apple's answer was to make joining a grid roughly as hard as joining a wireless network, then let the agent work only when the machine was otherwise unoccupied. It was a good piece of consumer-grade thinking applied to an institutional problem, and it is the reason small university groups used Xgrid instead of the serious schedulers, which were free but demanded a sysadmin.

~ what got buried with it ~

Xgrid was not removed on its own. Apple had announced the end of the Xserve in November 2010 and stopped selling it on 31 January 2011, and Mac OS X Server went from a separate operating system to a twenty-dollar download in the App Store. Read together, those are a company walking out of the machine room across about eighteen months, and Xgrid went out in the same stretch.

Macs were not what the labs around me ran in that decade. A Mac in Ankara in the mid-2000s was a design studio purchase or something a relative carried back from abroad, and anything doing real computation nearby ran Linux, which is still true in the work I do now. Xgrid's entire premise was that you already had thirty Macs sitting on thirty desks. That was never the room I was standing in, and by the time I was standing in rooms with real compute in them, the whole idea had moved to other people's data centers anyway.

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