In 1994 Professor Thomas Nicely, a math professor at Lynchburg College, was doing some calculations to enumerate prime numbers. After adding a Pentium to his collection of computers, he noticed some problems with his calculations. The problem was in the floating point divide unit. It occured only rarely, but can be duplicated. This is the most famous Intel CPU bug and Intel ended up agreeing to replace the faulty CPUs. Here are some articles about the problem.
Wikipedia Article (https://en.wikipedia.org/wiki/Pentium_FDIV_bug)
In 2014 Intel discovered a bug in how the Haswell and Broadwell Core microprocessors execute the TSX function. This feature could be used by developers to speed up multithreaded applications. The problem is hard-coded into the processors, so Intel's fix was to turn off the function.
A Mersenne prime is a prime number of the form p = 2k-1 for some k. Some examples of Mersenne primes are 3 (22-1), 7 (23-1), and 127 (27-1). The program Prime95 was written to find new Mersenne primes. The program has uncovered a bug in the Skylake processor.
In 2018, two security flaws were discovered in modern CPUs. These flaws are present in almost all processors developed in the last 20 years. Meltdown allows a user process to access kernel memory (a part of the operating system). Spectre allows an application to access the memory of another application. These are extremely serious security violations, potentially allowing the theft of any information, including passwords. These vulnerabilities are a result of features that speed up program execution. Operating systems have released patches and chip makers have released firmware updates to mitigate these flaws. The updates will cause a degradation in performance, but the extent of the performance hit depends on the type of processing. Chip makers are working on new designs to eliminate these problems.
Spectre and Meltdown Explained
How to Protect Yourself From Meltdown and Spectre
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