How does spark manage the memory of executor with multiple tasks

[canan chen]

Since spark can run multiple tasks in one executor, so I am curious to know
how does spark manage memory across these tasks. Say if one executor takes
1GB memory, then if this executor can run 10 tasks simultaneously, then
each task can consume 100MB on average. Do I understand it correctly ? It
doesn't make sense to me that spark run multiple tasks in one executor.