Sometimes at STH we come across server hardware that is nothing short of intriguing just because of a form factor. The HPE 620QSFP28 is one of those adapters. While many adapters have individual 25GbE SFP28 ports, this quad port adapter uses a single QSFP28 port. QSFP28 ports are commonly used as 100Gbps ports for 100GbE networking and one can normally break that 100GbE port into 4x 25GbE ports. Here, HPE is using the QSFP28 form factor to get around a practical design problem.

As a quick note, you can find these adapters also using HPE part numbers 840134-001 and 817762-B21.
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https://www.servethehome.com/hpe-620qsfp28-4x-25gbe-single-qsfp28-port-ethernet-adapter-review/