SSD - Upgrade from AHCI to NVMe to Extract Gains From Flash

Traditional computer systems read and write data to hard disk drives (HDD) using ATA or Advanced Host Controller Interface (AHCI) protocol. AHCI was designed for the physical behavior of a HDD - need time to spool up the platter, to find the first valid data on the platter, need time go to another place on the platter if the data is not stored contiguously on the platter.

But with the advent of solid state drives (SSD), the original ways of talking to storage using AHCI is outmoded.  That's why a new interface, designed for SSD, is needed. That is called Non Volatile Memory Express (NVMe).   It eliminates the overhead of the older protocol  - spooling up a platter, find first valid data on a platter - and  focuses on the strengths of SSD through lower latency and higher throughput.

There is also the PHYSICAL connection to consider. The traditional IDE/SATA/SATA Express physical connector interface is now replaced by PCIe.

Even with storage upgrades (HDD to SSD), other upgrades are needed as well. First, upgrade the HW interface (SATA->PCIe). Next, upgrade the SW interfaces (AHCI -> NVMe). Early Apple MacBooks had SSD drives, had PCIe interfaces, but didn't support NVMe yet.

Here you can see that a SW protocol can be mated with different HW protocol. For example, PCIe can support both AHCI and NVMe. On some of the Macbook Airs that I have used, the SSD is already connected to the SSD, but it is still using the older AHCI SW protocol. Apple has started to updated MacOS to support NVMe in the high end Macbooks. Hope to see this in Macbook Airs soon!