Spectre is a vulnerability that causes harm to modern microprocessors, which perform a prediction that guess in which direction a branch will go before it is known for sure. The Speculative execution has existed for a while in processors – but experts discovered that as the cache that is present on processors increases to keep up with their speed, so does the danger of abusing this type of defect.
The most typical form of speculative execution has to do with the way the program operates. The processor basically guesses that the control flow using a state of the art mechanism rather than waiting for all branch instructions to conclude, to determine which commands are needed to complete the task.
While It’s hard to repair these vulnerabilities, especially when it impacts an install base that’s so big, you can fix variants in the OS, as Google and Amazon have done for Spectre, to eliminate the problem, or can alter the microcode of the microprocessor itself, but that may make the system slower.