CSC300 / CSC402: What is memory? [8/9]

What does the machine memory look like when you see a picture like this:

To fully answer this question, you need to take the systems classes. But it is useful to have an idea of the memory, even if the details are not exactly correct.

Above, I show two parts of memory. On the left is storage for method calls (commonly called the stack), on the right is storage for objects (commonly called the heap). Arrays are objects in java. Machine addresses are shown as hexadecimal numbers beginning with the prefix 0x.

Each entry includes some overhead.

• For methods, the overhead includes the return address. This tells the machine what code should be executed when the method returns. If you are interested, you can read more.
• For objects, the overhead indicates the runtime type of the object. This is used to implement runtime type queries, such as the getClass() method. If you are interested, you can read more.