PSM4 (Parallel Single Mode 4) and SR4 (Short Range 4) are both optical transceiver technologies used in data center and high-performance computing environments, but they have key differences:

1. Fiber Type:

• PSM4: PSM4 transceivers use single-mode fiber (SMF). Single-mode fiber is designed for longer-distance transmission and is capable of carrying signals over larger distances with lower attenuation.

• SR4: SR4 transceivers use multimode fiber (MMF). Multimode fiber is suitable for shorter distances and is often used within data centers for connections that don't require long-range transmission.

2. Wavelengths:

• PSM4: PSM4 uses four parallel wavelengths in the 1310 nm range for both transmitting and receiving signals.

• SR4: SR4 uses four parallel wavelengths in the 850 nm range for both transmitting and receiving signals.

3. Transmission Distance:

• PSM4: PSM4 is typically used for longer-distance transmissions within the data center, with distances reaching up to several kilometers.

• SR4: SR4 is designed for shorter-distance transmissions within the data center, with typical distances limited to a few hundred meters.

4. Mode of Operation:

• PSM4: PSM4 uses parallel optics, where each of the four lanes operates independently, allowing for bidirectional communication on each lane.

• SR4: SR4 also uses parallel optics, but typically for shorter distances within the data center.

5. Application:

• PSM4: PSM4 is often used in scenarios where longer reach is required, such as connections between data center buildings or for connections that span multiple racks.

• SR4: SR4 is commonly used for shorter-reach connections within the same data center or inside a rack.

When choosing between PSM4 and SR4, it's important to consider factors such as the required transmission distance, the type of fiber infrastructure in place, and the specific needs of the network. Additionally, always refer to the specifications provided by the transceiver and network equipment manufacturers for accurate and detailed information.