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Structural Hazards

Structural Hazard: an interruption to a computation or flow of data owing to a physical resource that has insufficient capacity. Operations that could potentially be done in parallel have to be done serially.

Examples:

insufficient number ALUs for all of the operations to be schedulled in current clock tick.
insufficient number of ports on a RAM/register file.

Additional clock cycles and holding registers are typically needed. A Non-fully pipelined component: is unable to start a new operation on every clock cycle.

Such components:

Have a start input and a busy/ready output.
Component goes busy for a constant or variable number of cycles.

Example: fixed point multipliers and dividers (see additional material).

Example: all floating point operations tend to be implemented with multi-cycle units.