The "good memory" referred to is the cpu cache. Search for "L1 cache", "L2 cache" online. Here's a starting point: https://www.quora.com/What-is-the-L1-L2-and-L

The "good memory" referred to is the cpu cache. Search for "L1 cache", "L2 cache" online. Here's a starting point: https://www.quora.com/What-is-the-L1-L2-and-L3-cache-of-a-microprocessor-and-how-does-it-affect-the-performance-of-it-For-example-I-have-a-laptop-with-an-Intel-4700MQ-microprocessor-with-a-6MB-L3-cache-What-does-this-value-indicate?share=1 https://www.quora.com/What-is-the-L1-L2-and-L3-cache-of-a-mi...