The main difference between QSFP (Quad Small Form-Factor Pluggable) and QSFP28 lies in their data rates and applications. Both are form factors for high-speed data transmission in networking and data center environments, but they support different data rates.

1. QSFP (Quad Small Form-Factor Pluggable):

• Data Rate: QSFP modules are designed to support data rates up to 40 Gbps. They are commonly used for 40 Gigabit Ethernet (40GbE) connections.

• Applications: QSFP modules are used for various high-bandwidth applications, including connections between switches, routers, and other networking equipment within data centers.

2. QSFP28:

• Data Rate: QSFP28 modules are an evolution of the QSFP form factor and support higher data rates of up to 100 Gbps. They are commonly used for 100 Gigabit Ethernet (100GbE) connections.

• Applications: QSFP28 modules are used to meet the increased bandwidth requirements in modern data centers and high-performance computing environments. They provide a higher-speed alternative to QSFP modules.

Key Points:

• Compatibility: QSFP and QSFP28 are not directly compatible with each other due to the differences in the electrical and mechanical specifications. QSFP28 ports typically do not support QSFP modules, and vice versa.

• Backward Compatibility: Many networking devices and switches are designed to be backward compatible, meaning they can accept both QSFP and QSFP28 modules in their respective ports. However, the specific compatibility depends on the device and its specifications.

• Form Factor: Both QSFP and QSFP28 have a similar form factor, with four channels in each direction. However, QSFP28 modules have higher-density electrical connectors to accommodate the higher data rates.

• Evolution: QSFP28 represents the next generation of high-speed transceivers, offering increased data rates to meet the growing demands for bandwidth in modern data center environments. As network infrastructure evolves, there may be further iterations beyond QSFP28.

In summary, while both QSFP and QSFP28 are compact form factors used for high-speed data transmission, the key difference lies in the supported data rates, with QSFP supporting up to 40 Gbps and QSFP28 supporting up to 100 Gbps. The choice between them depends on the specific networking requirements and the capabilities of the devices in the network.