# Choosing master and slave boards

Some boards can drive clock signals more reliably than others and have more flexible clocking capabilities. If your system contains several board models, choose the boards with the best clocking characteristics for your primary and secondary masters.

The following list ranks the NMS boards by their abilities to serve as clock masters:

1. CG 6xxx family (best)

2. AG 4000, AG 4000C, AG 4040, and AG 4040C

3. AG 2000, AG 2000C, and AG 2000-BRI

4. CX 2000 and CX 2000C

5. QX 2000

For example, if your system contains a CG 6000C, an AG 4000C, and a CX 2000C board, the CG 6000C board should serve as primary master. The AG 4000C board should serve as secondary master. The CX 2000C board should act as a slave.

If you have more than one board of a given model, assign these boards as your masters before using any boards with poorer clocking characteristics. For example, if your system contains two AG 4000 boards and one AG 2000 board, the two AG 4000 boards should serve as primary and secondary masters. The AG 2000 board should act as a slave.