According to tech-journalists is the 256 GB SSD in the new Mac Book Air slower then the 512 GB SSD: Article

"While the M1 MacBook Pro and M1 MacBook Air have two NAND chips of 128GB each in its 256GB version, the M2 MacBook Pro – and now M2 MacBook Air – has a single 256GB NAND chip. In the first case, the M1 Macs can achieve faster speeds in parallel, while the latter fails to reach the same SSD speeds since it has only a single SSD."

Therefore it is recommended to buy a Macbook Air with 512 GB or larger.

But: Why is a single large chip slower then two smaller chips?

What's the precise reason?

  • The article gives the reason "n the first case, the M1 Macs can achieve faster speeds in parallel, "
    – mmmmmm
    Jul 31, 2022 at 7:25
  • If you need to work with large files at high speed, then you'll want more than 256 Gb anyway. If 256Gb of storage is within your data needs, then a disk speed of over 1400 MB/s is not going to be a limiting factor.
    – benwiggy
    Jul 31, 2022 at 8:14

1 Answer 1


SSDs are made up of so called storage modules (NAND chips). These NAND chips can differ in size. The "old" M1 MacBook Air had 2x128GB to achieve the total 256GB storage, the new one only has one 256GB NAND chip, while the 512GB model has 2x256GB. An end user never sees this while using a Mac, since the storage is simply presented as the total capacity.

Having two storage modules allows the computer to access both at the same time. I.e. imagine you have one thumb drive with 256GB capacity or two with each 128GB, but all other technical specs (i.e. read/write speed,...) are the same. In both cases your total capacity is the same. However, it is obvious that you can read data twice as fast with two thumb drives than with just one.

  • Thanks a lot. I've got it now: It can write on both modules simultaneously and accomplishes higher read-/write rates with that. I just wonder now: Why have Apple changed in it that way? Is it for pricing-reasons, because ONE large module is cheaper?
    – mizech
    Jul 31, 2022 at 8:51
  • @mizech don't ask Apple, ask the chip manufacturer.
    – Solar Mike
    Jul 31, 2022 at 8:51
  • @mizech That's something that only Apple and its suppliers will know; but there have been worldwide supply problems with chips over the last 3 years or so.
    – benwiggy
    Jul 31, 2022 at 13:47
  • @benwiggy Ahh ..., okay. Thanks! That makes at least some sense ...
    – mizech
    Aug 1, 2022 at 4:41
  • 1
    No. I think most Macs have two slots for the storage modules/SSDs, therefore a 2TB configuration will have 2x1TB.
    – X_841
    Sep 18, 2022 at 7:56

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