Multiple Readers/Writers

A hard drive that processes I/O requests from multiple sources experiences a different load than a hard drive that services I/O requests from only one source. The main reason for this is due to the fact that multiple I/O requesters have the potential to bring higher I/O loads to bear on a hard drive than a single I/O requester.
This is because the I/O requester must perform some amount of processing before an I/O can take place. After all, the requester must determine the nature of the I/O request before it can be performed. Because the processing necessary to make this determination takes time, there is an upper limit on the I/O load that any one requester can generate -- only a faster CPU can raise it. This limitation becomes more pronounced if the requester requires human input before performing an I/O.
However, with multiple requesters, higher I/O loads may be sustained. As long as sufficient CPU power is available to support the processing necessary to generate the I/O requests, adding more I/O requesters increases the resulting I/O load.
However, there is another aspect to this that also has a bearing on the resulting I/O load. This is discussed in the following section.