Data hazards
Data dependencies between instructions that are in the pipe at the same time.
For single pipeline in order issue: Read After Write hazard (RAW)
Add R1, R2, R3 #R1 is result register
Sub R4, R1,R2 #conflict with R1
Add R3, R5, R1 #conflict with R1
Or R6,R1,R2 #conflict with R1
Add R5, R2, R1 #R1 OK now (5 stage pipe)