Is there a big difference in speed between a SATA interface SSD connecting to a computer through a disk case and a direct SATA connection to a computer?

This depends on two things:

1. Disk box design and quality, including built-in chip algorithm, heat dissipation, etc. SATA interface cannot be directly converted to USB interface, but a chip is needed to convert and transmit data. If the algorithm is good, it can be achieved close to the SATA native rate (5Gbps, 8:10 encoding, about 500MB/s). In addition, the chip will inevitably produce heat. The overheated chip will automatically reduce the frequency to avoid burning itself. If the heat dissipation is good, it can always maintain high speed.

2. USB interface protocol (White's nightmare). To get SATA native rate, you need USB 3.0 and above. Hard disk and hard disk box again fast, interface speed card is also fast. It is not only the speed of the hard disk box interface, but also the influence of the computer interface speed, like the barrel effect, who is the slowest will be stuck.

Also note the characteristics of the hard disk itself. Some hard drives have a cache of their own, which can be very fast at first and then slow down a lot. This may not be a problem with the hard drive case, but the hard drive writes more data than the cache. This is also inevitable in the case of direct SATA connection to the computer.