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Get all the tools you need to upgrade the factory HDD of any 2009-2019 iMac to a larger HDD or a modern SSD.

SSD Performance: Sufficiency for the CPU Cores

Get OWC Aura and Aura Pro SSDs at (480GB and 960GB).


Following up on my review of the OWC Aura SSD upgrade for MacBook Air and MacBook Pro Retina, the question of performance arises: the upgrade is on par with the prior SSD in the MacBook Air for the real world test, but not as fast as the SSD in the late 2013 MacBook Pro Retina (and later models).

When is SSD performance an issue? Consider:

  • If too little internal capacity forces use of an external SSD, then the hassle factor increases, and the performance drops.
  • If the SSD can “feed” the CPU cores with enough data fast enough, then a faster SSD won’t help much.
  • Very few programs make more than relatively brief use of disk I/O. Moreover, the system caches a great deal.
  • Very few programs use all CPUs, so typically the I/O demands are throttled. This is a dual edged sword in which a very fast SSD can keep single-threaded tasks running faster. But it also means no top end performance (with only one CPU used).

Shown below, diglloydTools IntegrityChecker (command line version) is part way through checking 223GB of files. IntegrityChecker uses sophisticated multithreading techniques and thus can drive even a 12 core Mac Pro as fast as the drives can deliver data—gigabytes per second.

In this example there are only two real (non virtual) CPU cores in the MacBook Air 6,2, so 200% means full CPU usage*. With this MacBook Air, the CPU cores are the gating factor; a faster SSD would not get the job done faster.

Would an SSD twice as fast be better? Of course (and more expensive)—it would help fractionally with some tasks, being snappier. But this particular example is as I/O intensive as it gets, and the CPUs are already maxed-out. On faster 4-core MacBook Pro Retina, the SSD speed can be more of an issue, but it all comes down to usage, and if struggling with a too-small internal SSD, the benefits may accrue in favor of capacity. But perhaps now that the tech is solved, OWC will follow on with a 4-lane higher performance solution for demanding users?

* 4 virtual cores, but in real world tests, virtual cores look busy, but accomplish nothing as can be proven by disabling them with a developer tool so as to use only true hardware CPU cores.

Below, the 2 CPU cores in MacBook Air fully utilized with OWC Aura 960GB SSD.

CPU cores in MacBook Air 6,2 are fully utilized with OWC Aura 960GB SSD
(200% is full usage, virtual cores are extraneous)
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