Job and Task Scheduling In Hadoop

Job and Task Scheduling In Hadoop

I am little confused about the terms 'Job scheduling' and 'task
scheduling' in hadoop when I was reading the about delayed fair
scheduling.
http://www.cs.berkeley.edu/~matei/talks/2010/eurosys_delaysched.pdf
Please correct me if I am wrong in my following assumptions. 1.Default
scheduler,Capacity scheduler and Fair schedulers are only valid at job
level when multiple jobs are scheduled by the user. They don't play any
role if there is only single job in the system. These scheduling
algorithms form basis for "job scheduling" 2.Each job can have multiple
map and reduce tasks and how are they assigned to each machine? How are
tasks scheduled for a single job? What is the basis for "task scheduling"?