Fritzchens Fritz, a photographer famous for his high-quality die shots of processors, has managed to unlock an additional 128KB of L2 cache on AMD's ancient K6-2+ processor from 2000. The mod effectively turns the K6-2+ into its higher tier brother, the K6-III+. The method consists of decoupling capacitors responsible for enabling or disabling parts of the CPU's L2 cache.
For those that weren't around then, the original K6-2, which came out in 1998, was AMD's direct competitor to Intel's (at the time) flagship Pentium II processor. It featured a 250nm process and a specialized SMID unit designed to speed up 3D calculations, particularly useful for gaming. But the software required to power SMID called 3DNow never fully caught on like Intel's equivalent with its MMX software, which gave Intel a constant advantage with its Pentium II over the K6-2 and K-III in gaming performance.
The K6-2+ came out two years after the original K6-2, boasting a die shrink, allowing it to offer better performance at a lower voltage. However, contrary to its name, the K6-2+ wasn't on the same K6-2 microarchitecture. Instead, the K6-2+ shared the same microarchitecture as the K6-III+.
The K6-III+ changed the panorama back at the time. A 500 MHz core clock and an L2 cache size bump to 256KB outperformed the top-end Pentium II model, which clocked in at 450 MHz. But most of the chip's performance came from the additional clock speed uplift rather than the increased L2 cache size.
Good find on Vogons to enable the full amount of 256kb L2 cache for AMDs old K6-2+ CPU.SUCCESSFUL K6-2+ to K6-3+ Full Cache Enable Mod: https://t.co/Slt2CTLW2B#RETROCOMPUTER #AMD pic.twitter.com/EXTFpwGWnMFebruary 21, 2022
Since the K6-2+ and K6-III+ utilized the same microarchitecture, they were very similar. Only the L2 cache separated the two chips. The K6-2+ was a replica of the K6-III+ but with half the L2 cache. If this mod had been discovered 22 years ago, it would have been a gamechanger for sure.
All you have to do is relocate a capacitor to the right, as easy as it may look. For example, Fritzchens Fritz noted on Vogons forums how the K6-III+ has the bottom right-most capacitor installed to the right of the chip PCB. Meanwhile, the K6-2+ has that same capacitor slightly more left with a white-spaced opening remaining on the right.
Placing the capacitor to the same position as the K6-III+ allowed the K-2+ to enable the physically allocated 256KB of L2 cache fully. The modder confirmed that the CPU's cache level is fully functional and even noted his 3DMark2000 scores are higher.
But, enabling the additional cache isn't without some consequences. If you don't own a highly binned K6-2+ chip, it appears the chip can be unstable with all the cache enabled. Plus, there's also a chance the additional 128KB of cache is defective, which can cause further instability issues with the K6-2+.