Do you need a replaceable SSD?

Over the last few years, an increasing number of Macs have had internal SSDs and memory soldered in, and over the last two years with the addition of the T2 chip. For some users, these are bad news, and they’ll do anything they can to avoid ending up with one of these ‘new style’ Macs. This article looks at their benefits and penalties, with particular reference to SSDs and the T2 chip.

Hard disks

Although most new Macs don’t contain any hard disk (some iMacs still do, though), many of us were brought up with rotating hard drives as the standard medium for storage. Hard disks usually need to be replaced every few years, because they’re electro-mechanical devices which wear out, or sometimes even self-destruct in spectacular ways. They also have to operate inside sealed cases, to keep dust and dirt out. Accordingly, almost all computers with hard drives make provision for their replacement when they fail, if the user wants to increase their storage capacity, or replace them with an SSD.

With older computers fitted with a hard drive, adding external storage is never as good as increasing that fitted internally. For example, for many years the preferred external bus for Mac external storage was FireWire 400 and 800 (IEEE 1394), with a maximum data transfer rate of 3.2 Gbit/s, whereas internal SATA connections are normally capable of 6 Gbit/s, which is usually a good match for better performing hard disks.

Such has been the speed of development of hard drives that, over the three year period in which the great majority of hard drives should function well, for the same price (when new) the storage capacity might have doubled or tripled. If you bought an iMac 24-inch 13 years ago, the largest hard disk on offer for it was 750 GB. Three years later, the iMac 27-inch offered 2 TB maximum.


Many people imagine the SSD fitted inside their Mac is similar to those neat little SATA drives which are now so affordable and readily packaged inside the cheap enclosure of a portable external SSD. They’re not, and you wouldn’t thank Apple for using them. Look at the teardowns of recent Macs on iFixit, for example, and most now have the memory chips of the SSD soldered directly onto the logic board, or in the case of the iMac Pro, they’re special ‘blades’ apparently designed for that model.

The engineering reasons for Apple doing this include:

  • extremely high performance, in terms of read/write speeds;
  • low power consumption;
  • very low volume, allowing compact design.

Even if Apple were to mount these memory chips in sockets for ease of replacement, users would find it extremely hard to source compatible components. These aren’t the SSDs available from Amazon for a little over $/€/£ 100 per TB.

Their extreme performance comes from the fact that these soldered-in SSDs don’t use a regular controller chip: that’s one of the functions of the T2.

T2 as disk controller

Traditional designs would match the SSD with a controller chip, through which all data has to pass to and from the memory chips themselves, then perform any encryption either using another chip, or the CPU itself. In Macs with a T2 chip, the T2 functions as both the controller for the memory chips which make up the SSD, and performs encryption/decryption in hardware. For the latter, it features a secure enclave which ensures that its keys are safe, and the encryption cannot be broken.

Hardware encryption means that there is essentially no detectable overhead when using FileVault on your internal storage, and that it is completely transparent to software running on the Mac. To achieve this, there is no unencrypted mode: data transferred to and from internal storage is always encrypted and decrypted.

If you choose not to enable FileVault, then the encryption key used is determined by the T2 and stored in its secure enclave. Enabling FileVault doesn’t require the data in the SSD to be re-encrypted, but needs your password in order to access the stored key in the enclave. This means that full FileVault encryption comes free, and without any performance overhead.


With its SSD and T2 chip soldered in, and the T2 required to access the SSD and decrypt its contents, failure of either is a failure of both, and requires a new logic board. Indeed, any failure which requires replacement of the logic board necessarily loses all data stored in the SSD. If you buy a Mac with a T2 and fixed internal storage, then AppleCare is a wise investment, although very few Macs need replacement logic boards during their first three years.

Compared to rotating hard drives, SSD failure rates are so low as to be negligible. Most failures occur early, in the first hundred hours of use, or when the SSD is reaching the end of its working life, which should be after ten years or more, long after your Mac will have gone for recycling.

More common (although still extremely unusual) is the situation where the T2’s firmware becomes damaged or corrupted. Although there is a procedure to restore its firmware, that doesn’t always work. The danger is greatest if you run macOS beta releases which include BridgeOS firmware updates beyond those of the last public release. That can ‘brick’ the Mac until a newer public release is available. Hopefully Apple is addressing this issue which did affect some users who installed Catalina betas.

Any computer, even a high-end Mac, can die suddenly and require extensive hardware repair including a replacement logic board. There’s no evidence that Macs with T2 chips are any more likely to suffer that, and the same precautionary measures are required in any case: good backups. Soldered-in SSDs and T2 chips don’t alter that in the slightest.

Nor does the SSD and T2 have any bearing on the right to repair: since Apple’s modular engineering design in the Mac II, repair is normally performed by replacing the defective board or system with a spare supplied by Apple on an exchange basis. If you really want to fix your own MacBook Pro, there’s no inherent reason that you couldn’t do so. But the era of technicians waving hot soldering irons over defective components has long since gone, I’m afraid.


If you’re extremely unlikely to need your Mac’s logic board replaced, what about increasing storage capacity when you can’t augment or replace internal storage?

Since the days of FireWire 400 and 800, external connections have improved greatly in speed. All Macs with T2 chips now have Thunderbolt 3 ports, which support data transfer rates up to 40 Gbit/s, more than ten times faster than FireWire 800, and more than six times faster than the best available through a SATA interface.

For everyday storage, external SSDs with SATA 6 Gbit/s access, connected via USB 3.1 Gen 2 are far cheaper than any internal expansion and more than quick enough. For more demanding use, turn to external SSDs comparable to Samsung’s X5 connected by Thunderbolt. These are considerably more expensive, and closer to the likely cost of any internal expansion.

Ensuring that your internal SSD is capacious enough to accommodate macOS, most apps, and other files which benefit from its performance, there is greater flexibility and lower cost in using external storage for future expansion. Exceptions to this include users who need high performance when processing very large files; they’re probably best waiting for the new Mac Pro.

Security and theft

In many parts of the world, Macs are attractive items to thieves, all too often the choice of the professional. Although the casual thief may be unable to tell a Mac Pro from a mini, no professional should waste their time trying to steal a T2 Mac protected by a FileVault password and Secure Boot. As it’s impossible to break into one, its only value to a thief is for sale as spare parts.

Even better than that, provided that you activate FileVault with your password to protect internal storage, anyone who does steal your Mac will be unable to access any of the data on its internal storage. This is probably most important for those travelling with their MacBook Pro or MacBook Air.

What about the iMac then?

The T2 chip is a disk controller for internal SSDs. Base iMacs can currently be configured with a traditional 1 TB rotating hard drive, a Fusion Drive, or SSD. I don’t think you’ll see iMacs coming standard with T2 chips until Apple drops the hard disk and Fusion Drive options, which is a pricing and marketing decision. It also provides an option for those Mac users who need to buy a new Mac but won’t accept one with a T2 chip. After reading this, I hope that doesn’t include you.

I have a T2-equipped iMac Pro, and a MacBook Pro without a T2. Although some of the habits of the T2 are still quite worrying at times, I have enabled FileVault, and next year intend replacing the MacBook Pro with a similar Mac with a T2 chip. It is a big step forward.