In A Deepness in the Sky, the Arachnids discover diamond nano-tech particles mixed in with shale formations from the ancient past of the planet. When sifted from the surrounding shale, the nano-tech apparently reactivates and exhibits anti-gravity properties (becoming a material known as "cavorite").
However, in A Fire Upon the Deep, we are told that some technology, including agrav, can only be built in the High-Beyond and Transcend:
"The Beyond and below are like a deep of ocean, and we the creatures that swim in the abyss. We're so far down that the beings on the surface -- superior though they are -- can't effectively reach us. Oh, they fish, and they sometimes blight the upper levels with poisons we don't even understand. But the abyss remains a relatively safe place." She paused. There was more to the analogy. "And just as with an ocean, there is a constant drift of flotsam from the top. There are things that can only be made at the Top, that need close-to-sentient factories -- but which can still work down here. Blueshell mentioned some of those when he was talking to you: the agrav fabrics, the sapient devices. Such things are the greatest physical wealth of the Beyond, since we can't make them."
Not only can the only be created in the High-Beyond or Transcend, but they also apparently require being in those zones to maintain long-term functionality
In the Middle Beyond:
At Sjandra Kei the annual income of an academician might pay for a square meter of agrav fabric -- junk that might not last a year. Here there were millions of hectares of the stuff, supporting billions of tonnes. Just replacements for dead fabric required more High Beyond commerce than most star clusters could command.
In the Low Beyond:
It was a team game the two Skroderiders played. While Blueshell chattered, Greenstalk watched everything around them, running her skrode's recorders on all bands, trying to place this environment in the context of others they had known. Technology: What would these people need? What could work? In space this flat, there would be little use for agrav fabric. And this low in the Beyond, a lot of the most sophisticated imports from above would spoil almost immediately. Workers outside the long windows wore articulated pressure suits -- the force-field suits of the High Beyond would last only a few weeks down here.
And in the Slow Zone:
"That's only part of it. I think we Tines are more flexibly minded than the poor Two-Legs. Can you imagine what it will be like when we make more radio cloaks, when we make our own flying machines?"
Woodcarver smiled, a little sadly now. "Pilgrim, you dream. This is the Slow Zone. The agrav will wear out in a few years. Whatever we make will be far short of what you play with now."
How does the cavorite maintain its function in the OnOff system, which is clearly in The Slow Zone (and was, at one point, in The Unthinking Depths), despite the cavorite being millions of years old?