What if need more storage space on your Mac, but upgrades are
impossible or too expensive, or an externally connected drive
won’t do? The SD Card slot found in many older and some newer
Macs is worth looking at as an option.
In recent years, Apple has shifted from Macs that can have
internal storage upgraded to higher capacities or from a hard
disk drive (HDD) to an SSD—though sometimes with a fair amount
of difficulty—to storage that can’t be modified after purchase.
Even on Macs that offer some degree of drive upgradability, you
may still feel stung by SSD prices. My wife recently acquired a
mid-2014 MacBook Pro with an easily swappable 500GB SSD module.
But upgrading to 1TB? The price tag is over $400. (SSD modules
that work with other computers can be as little as $150 for the
same capacity, but those aren’t compatible with Apple’s slot.)
For Macs with a slot that holds SD cards, you can take
advantage of inexpensive, relatively fast, high-capacity cards
to extend your internal storage and have an “external” drive
that’s just as portable and integral as the one built into your
If you don’t use a standalone camera to shoot, you might be
unaware that capacities have grown from 32GB and 64GB to 256GB
and 512GB while prices have dropped ridiculously. The sweet
spot is 256GB, which can cost from $60 to $80 at online stores;
512GB cards are typically at least $200. If you’ve got a Mac
with just a 128GB drive, you might find a $20 to $30 128GB SD
Card could fit your needs.
While these cards may come formatted in a Windows-specific or
universal format for Macs and PCs, you can reformat to “Mac OS
X Extended” (HFS+) in Disk Utility, and use them just like any
other Mac volume. Apple has
an extensive support page about the SD card slot, which is
a sort of shortcut name for a variety of card formats that can
fit and conform to a set of standards.
And Apple explicitly answers the question about whether you
could even switch to an SSD as your startup volume: Yes! Make
sure it’s both using the GUID partition format and Mac OS X
Performance and accidental ejection
Two things you should consider about an SD Card: performance
and accidental ejection.
The 256GB cards typically have a rated performance of 90 or 100
megabytes per second (MBps). That’s comparable to a 5400 rpm
HDD, so not very fast. This is further constrained in laptops,
where the models Apple has offered with a card slot rely on USB
2.0 for data transfer. That’s 480 Mbps or roughly 60 MBps,
which can feel painful for loading large files or life
interaction. But it can be good for material you’re not writing
and rewriting a lot at high speed—notably an iTunes or Photos
library. (Apple dropped the SD slot in the MacBook Pro starting
with 2016 models. The MacBook Air and 2015 and later MacBook
never included an SD slot.)
Desktop Macs with a card slot, like an iMac, use the PCIe bus.
This data-transfer method performs far faster, and won’t
constrain a high-performance SD card.
Ejection is the other worry, because these cards are designed
to be easy to remove and may even stick out of the slot. On a
desktop, it’s less of an issue, because the slot is fairly
shallow. On laptops, however, if you have a card that protrudes
(as most do), you might jar it and accidentally dislodge it.
If you’re actively writing data to the card or it has open
files on it when it’s ejected unintentionally, this can cause
data loss or other problems to the drive. Those should be
repairable via Disk Utility, but it’s still a risk.
Thanks to Macworld reader Kraig for suggesting this Mac 911
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