describe clustering and high availability

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@@ -116,7 +116,21 @@ Instructions: Please answer the following questions in complete sentences. Your
     other operations, the device driver returns status information.
 
 1. Why do clustered systems provide what is considered high-availability service?
-1. Describe an operating system’s two modes of operation.
+
+    Clustered systems gather together multiple CPUs to accomplish computational
+    work. Clustered systems differ from multiprocessor systems in that they are
+    composed of two or more individual systems joined together.
+
+    Clusted computers share storage and are closely linked via a local area network.
+
+    A high availability service will continue even if one or more systems in the cluster
+    fail. HA is generally obtained by adding a level of redundancy in the system.
+    A layer of cluster software runs on the cluster nodes. Each node can monitor one or
+    more of the others. If the monitored machine fails, the monitoring machine can take
+    ownership of its storage and restart applications that were running on the failed machine.
+    The users and clients of the applications see only a brief interruption of service.
+
+1. Describe an operating system's two modes of operation.
 1. Define cache, and explain cache coherency.
 1. Describe why direct memory access (DMA) is considered an efficient mechanism for performing I/O.
 1. Describe why multicore processing is more efficient than placing each processor on its own chip.