PLANET NVR-420 - Manual (Page 11)

4. One side of the housing can be detached as shown below.
5. Install the HDD by sliding it into the tray diagonally to avoid the tray separator.
6. Once the HDD is placed into the tray, you can see a gap between the HDD and the SATA connector.
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4-CH H.264 Network Video Recorder with HDMI
User’s Manual of NVR-420