COMSARC

A Data Dependency is roughly a condition where the value of a calculation in the future is based upon a calculation being made now.
Data dependencies play a big part in much of Computer Science/Engineering. Data dependencies (data hazards) can be created in pipelined code, required data forwarding or stalling of a modern pipelined microprocessor. Data dependencies can cause race conditions in parallelized code. Also, compilers nowadays frequently tries to unroll loops, and detecting data dependencies can allow the compiler to perform several optimizations.
DefinitionThere are four basic types of data dependency, frequently called different things based on what part of computer technology they are being used in.
1. Flow Dependence - A value is written then read
2. Anti Dependence - A value is read then written
3. Output Dependence - A value is written, then written over
4. Read Dependence - A value is read, then read again. It is not an issue, included for thoroughness