From the article: >> Starting in the mid-2000s, Intel added a layer of security within its chips and began encouraging developers to store users’ most sensitiv

From the article: >> Starting in the mid-2000s, Intel added a layer of security within its chips and began encouraging developers to store users’ most sensitive information in the walled-off area rather than in regular software memory. Can anyone explain what the author is referring to as "walled-off" area? L1, L2 Cache?