Which component should be checked first if a Unix server completes POST but halts with a transport error?

In the scenario where a Unix server successfully completes the Power-On Self-Test (POST) but then halts due to a transport error, the first component to check would typically be the hard drive. A transport error suggests that there is an issue with data transfer, which can be directly related to the hard drive’s functioning.

This could involve checking the connections to the hard drive, the interface it uses to communicate with the motherboard, or potential failures within the drive itself that could prevent the server from accessing the data required to boot successfully. Since the hard drive is crucial for loading the operating system and other critical data required for normal operation, any malfunction here would lead to boot issues manifesting as transport errors.

While the other components listed, like the video card, cooling fan, and memory, play significant roles in system functionality, they are less likely to specifically cause a transport error after a successful POST. The video card could lead to display issues, the cooling fan is vital for thermal management, and memory issues typically cause different types of errors at boot. Thus, focusing on the hard drive is the most logical and effective first step in troubleshooting this specific error.