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+# Preface
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+There many been many developments in distributed systems, databases and the applications build on top of them, there are various driving forces:
+
+1. Handling huge volumes of data.
+2. Businesses need to be agile, test hypotheses cheaply and respond quickly to markets.
+3. Free & open source software has become very successful and is preferred now to commercial or in-house solutions
+4. CPU clock speeds are barely increasing. But multi-core processors are standard and networks are getting faster. Parallelism is only going to increase.
+5. Even small teams can now build systems that are distributed across machines and regions - thanks to **IaaS** (think *AWS*)
+6. Many services are expected to be highly available. Extended downtime is unacceptable.
+
+An application is *data-intensive* if data is it's primary challenge.
+
+- The quantity of data.
+- The complexity of data.
+- The speed at which data changes.
+
+This is opposed to *compute-intensive* where the CPU is the bottle neck.