Convert SATA port from IDE to AHCI - Question

AHCI vs IDE is a BIOS setting, so I don't think you can run the boot drive in IDE mode while the second drive is in AHCI mode. They both have to be AHCI or both IDE.

It is well worth doing the registry fix so you can run both SSDs in AHCI mode. AHCI enables NCQ - native command queuing. This allows the computer to send multiple requests to the SSD simultaneously, and the SSD completes them as quickly as it's able. Unlike HDDs where the primarily limitation on small file accesses are seek time and rotational latency, SSDs are actually able to complete small file read/write requests faster than the computer can request them (the request has to go through multiple layers of the OS and filesystem before reaching the drive, which takes time).

In other words, in IDE mode, the computer requests a small file be read, the SSD fetches it and returns it. Only after the first data request has bee completed does the computer begin putting together the next small file read request, during which time the SSD is sitting idle. In the benchmark you've posted, this limits 4k read/writes to 30 and 57 MB/s.

In AHCI mode, the computer puts together a bunch of small file read requests in parallel, and sends them all to the SSD at once (queuing them). The SSD then gets busy reading them and sends the data back to the computer - no idle time between file accesses. That's the 4k-64Thrd benchmark in your pic - 64 threads = 64 simultaneous requests. Because you're in IDE mode, the number isn't that different from a regular 4k read/write request. Compare to a SSD where AHCI mode is enabled:



370 MB/s 4k reads, 141 MB/s 4k writes. Substantially better than your 850 EVO in IDE mode. (In reality your performance boost will not be this big because nothing except a benchmark program is going to throw 64 access requests at your SSD at once. But things like a virus scan can easily fill up the queue with a dozen simultaneous requests, and the speed increase will be substantial over IDE mode. Likewise if you're copying a bunch of small files from one SSD to another.)

Yes,if on same controller.

There may be couple of different SATA controllers on the MB. For instance one built into SB/Chipset and another like separate Marvel controller chip. One of my MBs have 3 separate ones and each one can be set differently.