Last Week on My Mac: M what?
If you’ve become blasé with the tail end of the summer’s sport, Olympics and Paralympics, events next week should make compulsive viewing. Apple starts with its regular September launch of iPhones, and a day later we’ll be enthralled by the first TV debate between the two main contenders in the US presidential election. My money is on the iPhone 16 to win.
With those new iPhones comes the next major version of iOS, and hot on its heels macOS Sequoia 15.0. Without its AI features, that might seem the least exciting announcement of the week, but it prepares the ground for the next batch of Macs to be announced most probably in October, for shipping the following month. All commentators seem agreed that they will come not with M3 chips, but will be the first Macs to use the M4 family.
By now, different M-series chips are becoming blurry, so I’ll try to draw distinctions between them, and suggest why Apple has rushed through the M3 as if it might have been better-named the M2.5.
M1, November 2020
Skipping silently over Apple’s Developer Transition Kit from the summer of 2020, Apple silicon Macs started at a leisurely pace, as the four members of the M1 family rolled out over nearly 18 months. Their CPU cores ranged from the base version with 4 P and 4 E cores, 4P+4E in short, up to the impressive Ultra at 16P+4E. There was little separation, though, between the Pro and Max versions, which both came with 8P+2E, and only really differed in their GPUs. Thus, in the M1 there only two fundamentally different CPU core configurations, 4P+4E and 8P+2E, each with up to four cores in a cluster. Both core types used Arm’s instruction set architecture (ISA) from 2018, designated ARMv8.5-A.
M2, July 2022
Some of us assumed that first cycle would prove the model for its successors, but we were wrong and getting wronger as time progresses. After a break of just four months, Apple leaped into the M2 cycle, which it shortened to just a year from the 4P+4E M2 base version in July 2022. This cycle Apple bumped the number of E cores in the higher versions, taking the Ultra to 16P+8E, but still leaving little distance between the Pro and Max versions, both with 8P+4E, and two fundamental core configurations and clusters of four.
What might have appeared at the time to be small change, an increment in the ISA to ARMv8.6-A from 2019, brought enhancements in matrix maths, support for bfloat16 numbers to help with AI, and additional virtualisation capability. Although the M2 series appeared evolutionary in performance, it has also proved more capable.
M3, November 2023
Introduction of the M3 came again after a brief break of around four months, in November 2023. This time there was no phased release, gradually building up through Pro and Max to Ultra. The lesser three all came together, and put more distance between Pro and Max versions. The base M3 stuck with the proven combination of 4P+4E, the Pro scaled up to 6P+6E, then the Max nearly doubled that at 12P+4E, making three fundamental core configurations. That was over nine months ago, and there’s still no sign of any doubled-up Ultra version. To match the M3 Pro and Max core counts, they now form clusters of up to six cores, a significant advance on the two previous families.
While the M3 kept to Arm’s ARMv8.6-A ISA, Apple redesigned the GPU to support Dynamic Caching, Mesh Shading, and hardware-accelerated ray tracing. There’s one oddity, though: as this is the same ISA as the M2, with its enhanced support for virtualisation, Apple has stated that nested virtualisation coming in Sequoia requires not an M2 chip, but the M3, with its identical ISA. I have yet to see an explanation for that requirement.
M4, May 2024
In the absence of any M3 Ultra, Apple caught us off-guard when in May of this year (only six months after the M3) it launched new iPad Pros with what we must assume is the base M4 version of 4P+6E, and the next Arm ISA of ARMv9.2-A from 2020. That enhances vector and matrix maths, and brings support for 1 GHz timers, enabling nanosecond time resolution. In addition to the GPU features added in the M3, those in the M4 now also have hardware accelerated AV1 decoding.
There have, of course, been many other changes between M1 and M4, including higher operating frequencies for CPU cores, growth in the capability of the neural engine (ANE), and better support for external displays in the base version.
M1 to M4
Assuming that we’re soon to be treated to a range of Macs running members of the M4 family, the pace of change is accelerating. Landmarks along the route so far include:
Increased E cores and ARMv8.6-A ISA in the M2.
Three core configurations, clusters of six cores, and extended GPU hardware support in the M3.
Increased E cores, ARMv9.2-A ISA and extra GPU hardware support in the M4.
For those who have whetted their appetite for Apple silicon with an M1 or M2, the leap up to M4 should prove exhilarating. Bring on the M4 Mac Studio, please, no matter who ends up as President.
