Last Week on My Mac: Do M2 Macs need better storage support?

By now, Apple has already finalised the design of its successors to the M1 series, which are surely due to be revealed in just over a month’s time at WWDC. One vital question is whether and how it will support faster storage, in particular standards such as PCI Express (PCIe) 5.0.

Current M1 models show only too vividly the shortcomings of the standard we all hoped would solve the many problems of USB, Thunderbolt 4. Whatever the exact explanation, data transfer rates between M1 models and Thunderbolt 4 storage can’t exceed 3 GB/s, and generally range from 1.5 to 2.6 GB/s. Compared with hard disks, typically around 0.15 GB/s, those might appear impressive, but today’s NVMe SSDs can rival Apple’s expensive internal SSDs when given the chance, which requires a suitably fast interface rather than Thunderbolt 4.

Following a ‘leak’ late last year, there’s widespread speculation that Intel is preparing Thunderbolt 5, which is expected to offer a combined total of twice the bandwidth of Thunderbolt 3 and 4, at 80 Gb/s. If that proves correct, and it suffers the same diminishing returns as those current versions, that alone will deliver no more than 6 GB/s for connected storage, still well short of the SSDs already available in M1 models, and less than some current NVMe SSDs such as Samsung’s 980 Pro, which costs less than $/€/£ 140 per TB.

Although not yet widely available, PCIe 5.0 can deliver as much as 63 GB/s over 16 lanes, and Intel has already announced that its 12th generation Intel Core processors will support this standard, and start shipping by the end of this year. Those are the same processors which come with various combinations of P and E cores, and are intended to compete directly with Apple’s successors to the M1 series.

Supporting an internal interface like PCIe 5.0 poses Apple a major design problem: so far, no M1 model supports any form of internal expansion. Even the $/€/£ 4000+ Mac Studio Ultra doesn’t offer this, although it might eventually arrive in the form of special SSD modules to be installed in its internal slots. None of Apple’s current cases, apart from the Mac Pro, are designed to give the user ready access to install storage internally, and their internals aren’t intended to accommodate current or projected presentations of PCIe storage devices, such as the popular M.2 format.

Direct external PCIe hasn’t been particularly successful either. ePCIe hasn’t yet surpassed PCIe 2.0 speeds, and OCuLink’s latest version only caters for eight lanes of PCIe 4.0, although even that would be an improvement on Thunderbolt 5, it seems.

All this presumes that Apple is prepared to compromise its lucrative trade in soldered-in SSDs. With their current maximum capacity of 8 TB for the additional cost of more than $/€/£ 2000 – that’s another whole Studio Max – that might be a sacrifice it isn’t prepared to make.

Backing up such capacious internal SSDs is another issue that Apple needs to address. Here large and fast external storage is essential, but Time Machine is far out of its depth because its I/O is throttled, and can’t make best use of existing Thunderbolt 3 devices.

Successors to the M1 series of chips need much better high-performance storage options, or they risk becoming like exotic sports cars, exciting for the occasional weekend away, but useless for shopping. Incorporating support for PCIe 5.0 is one way Apple could do that, but that would also require commercial and design changes which could prove unconscionable to Apple.