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Comment by dfox | Hacker News Reader

This is pretty common practice to increase yield by using only partially working parts that are still usable in limited way. While 486DX/SX is prime example, there are lots of other:

Original Xbox used marginal DRAM chips and detected by software on each boot which regions of memory are actually usable.

AMD's current CPUs with "weird" number of cores (3, 6, 12..) are produced by disabling cores that does not pass tests.

Cell BE as used in Playstation 3 has one SPU disabled for same reason.

While in most cases such disabling is done by blowing some fuses in hardware I can imagine that in embedded systems software only solution (like the Xbox one) is actually more convenient.

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Adittionally, probably the most famous example is the Celeron range.

Celerons were originally Pentium IIs with large segments of the cache fused off, unusable due to defects. However they turned out to be so popular that Intel started to disable the cache of otherwise good cores, and then later began specifically fabbing them, to meet the demand.

For me, the most famous example is DRAM chips in Sinclair ZX Spectrum. Sir Clive got them cheap because they were ones rejected at the production test. Spectrum issue 1 48 K model used 64 kbit chips where one half was broken, and the motherboard was then wired to only use the other half.

That was a time when hardware, particularly memory, was expensive. This was in 1982.

Not exactly. Celerons began as straight up Pentium IIs designed to operate without any L2 cache. They didn't have great performance but were crazy cheap to make and super easy to overclock. Then they started cramming in just a little bit of on-die L2 cache (about 1/4 of the minimum for a regular Pentium II) to help out performance. This turned out to be wildly successful, and eventually this formulation (one chip with on-die L2 cache) became the predominant design for the mainline Intel micro-processors. Afterwards the Celeron family of processors were identical to retail Pentium/Core cpus but with sections of cache disabled, reduced clock rates, etc. (either due to binning by defects or intentional deactivation).

Interestingly, Intel now offers "upgrade cards" for low-cost CPUs whereby components are deactivated via firmware or suchlike and special codes can be entered into the bios screen to turn them on (for a price, of course).

Ah, it seems you're right - thanks for correcting me.

And of course GPU vendors also employ similar techniques. It is not uncommon to see the same chip in multiple models, with lower-end models with parts of the chip disabled either due to defects or for product differentiation.

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