How does the master step start the slave steps locally?

[zhan]

When I using the partition step on spring batch, I confuse between the master and slave step!
On the document saying, the master step can start the slave step remotely using the middleware such as JMS.
I don't know about how to config the spring batch using the JMS.But in my mind if we using the JMS, the slave step is running on a separate JVM which is differente from master step!
So the following is my questions:
When the master step start the slave steps locally, what is the middleware using for?
Is there a middleware that can share the memory?
Is the slave step also running on separate JVM?Or local muti-threads?
Here is my simple master step definition, that is runing well on spring batch admin!
<job id="job1" xmlns="http://www.springframework.org/schema/batch">
<step id="asyncStep">
<partition step="slaveStep" partitioner="myPartitioner">
<handler grid-size="2" task-executor="taskExecutor" />
</partition>
</step>
</job>

[zhan]

As reading more document, I don't confuse now.
I am clear about such issues!
Thanks