Modern CPUs have a backstage cast
&gt; It&#x27;s responsible for initialising the chip and getting it out of bed enough to the point where at least one of the main cores can run using cache-as-RAM mode<p>The somewhat surprising but true implication is that on boot, the CPU is initialized before the RAM is initialized. So there is a window of time during boot when the main core on the CPU is running instructions that cannot access the RAM. Even on register-starved x86 it is possible to write code without using RAM, but it certainly seems more convenient to me to treat the cache as RAM.<p>Documentation for a special compiler that compiles to code that doesn&#x27;t use RAM: <a href="https:&#x2F;&#x2F;github.com&#x2F;wt&#x2F;coreboot&#x2F;blob&#x2F;master&#x2F;util&#x2F;romcc&#x2F;romcc.1">https:&#x2F;&#x2F;github.com&#x2F;wt&#x2F;coreboot&#x2F;blob&#x2F;master&#x2F;util&#x2F;romcc&#x2F;romcc....</a>