You can clearly see the stacks for each thread, the heap, and (right on the last row) the IRQ stack.

The upper thread is simply printing the timer value, and the lower one is printing the Tick / Tock messages.

Max stack usage (per thread) is ~70 bytes. Interrupts can occur concurrently.

Other notable locations in RAM - near the bottom of the heap are a few static variables, followed by the 11 byte buffer printf() uses to format decimals, and then the two bytes of the timer high word.