IIRC the Celeron chips coming out of the fabs tested better than Intel expected with far more of the batches being rated as stable as higher-spec units. This le

IIRC the Celeron chips coming out of the fabs tested better than Intel expected with far more of the batches being rated as stable as higher-spec units. This lead to a shortage of cheaper units that people were trying to buy and an excess of faster units that people didn't want to pay for. To avoid both missing sales and having a lot of stock sat in warehouses, many batches of Celeron chips that had tested fine to be sold as the faster models were binned with those that were only rated for the slower speeds. This meant that if you were lucky you could safely overclock the cheaper units by officially extravagant amounts, without extra special cooling arrangements or other hacks, and many did. You could tell (at least initially, I'm not sure if Intel changed this later) from part of the product code that you definitely had one of the units from a batch that tested fine at the higher speeds, so it wasn't that much of a gamble either. We referred to them as Silly-ron CPUs.