3 ms·

How does this fusing work? I assume there are a bunch of wires than are either hot or ground and that determines if part of a chip gets run?

PeterisP 6y ago
I believe you design special fuses on the chip that can be "blown" with a laser after testing and before putting the silicon in the protective packaging.
- p_j_w 6y ago
  Fuses aren't blown with a laser, it's purely electrical. You apply a sufficiently high voltage to some port on the part from a source that can drive a high enough current and then tell the digital block of the chip which address to fuse and if you want it high or low. Repeat for the entire fuse bank and you're done. https://en.wikipedia.org/wiki/Efuse https://en.wikipedia.org/wiki/Efuse
mechagodzilla 6y ago
It might actually use a traditional fuse block, where at some point in the packaging/testing process, you literally apply a sufficiently high voltage that you can permanently 'set' some part of it (whether that's actually melting a tiny wire, I'm not sure). But that's basically just programming a ROM that gets read in at boot time, and sets a bunch of logic on the chip to route around the bad parts. You could just use an external EEPROM to track that info too, and it would basically work the same.
- andrewf 6y ago
  20 years ago people were overclocking AMDs by drawing on them with pencil: http://www.ocmelbourne.com/tutorials/PencilTrick/ http://www.ocmelbourne.com/tutorials/PencilTrick/ This last decade people soldered resistors onto cheaper NVIDIA cards, to make them behave as more expensive NVIDIA cards: https://www.eevblog.com/forum/general-computing/hacking-nvidia-cards-into-their-professional-counterparts/?PHPSESSID=3kesesdcd2gp8tftrkiihn6ef2 https://www.eevblog.com/forum/general-computing/hacking-nvid... So chipmakers have an incentive to bury the process in the chip and make it irreversible.

PeterisP 6y ago

I believe you design special fuses on the chip that can be "blown" with a laser after testing and before putting the silicon in the protective packaging.

p_j_w 6y ago
Fuses aren't blown with a laser, it's purely electrical. You apply a sufficiently high voltage to some port on the part from a source that can drive a high enough current and then tell the digital block of the chip which address to fuse and if you want it high or low. Repeat for the entire fuse bank and you're done. https://en.wikipedia.org/wiki/Efuse https://en.wikipedia.org/wiki/Efuse

mechagodzilla 6y ago

It might actually use a traditional fuse block, where at some point in the packaging/testing process, you literally apply a sufficiently high voltage that you can permanently 'set' some part of it (whether that's actually melting a tiny wire, I'm not sure). But that's basically just programming a ROM that gets read in at boot time, and sets a bunch of logic on the chip to route around the bad parts. You could just use an external EEPROM to track that info too, and it would basically work the same.

andrewf 6y ago
20 years ago people were overclocking AMDs by drawing on them with pencil: http://www.ocmelbourne.com/tutorials/PencilTrick/ http://www.ocmelbourne.com/tutorials/PencilTrick/ This last decade people soldered resistors onto cheaper NVIDIA cards, to make them behave as more expensive NVIDIA cards: https://www.eevblog.com/forum/general-computing/hacking-nvidia-cards-into-their-professional-counterparts/?PHPSESSID=3kesesdcd2gp8tftrkiihn6ef2 https://www.eevblog.com/forum/general-computing/hacking-nvid... So chipmakers have an incentive to bury the process in the chip and make it irreversible.