Memory speed iMac 2-15 10-40 Mb/sec. Why?

Question

Solid State Drives

I bought a 2015 Imac with a 4-core Intel Core i5 processor and 8GB of RAM. Initially, it worked flawlessly, but after a while wild brakes began. Our digging, I realized that the problem was in hdd, I missed a couple of programs, it turned out that the write and read speed was only 10-15 mb / s. I thought that the problem was in the hdd and decided to buy an external ssd and (480 GB SSD drive Kingston A400 (SA400S37 / 480G)) put it in (external case 2.5" SATA AgeStar SUB2O1 (SILVER), USB 2.0, aluminum). The result improved, the speed of reading and writing is now 30-40 mb / s, but I still don’t understand what is the reason, because even through an external ssd the speed should be 300-400 mb / s.

Answer 1

USB 2.0 speed limit - about 40 MB / s
connect via USB 3.0 or Thunderbolt