In the light of recent news, you might now be wondering whether you can afford to wait until next year in the hope that Apple then releases the M4 Mac of your dreams. To help guide you in your decision-making, this article explains what chip options are available in this month’s new M4 models, and how to choose between them.

CPU core types

Intel CPUs in modern Macs have several cores, all of them identical. Whether your Mac is running a background task like indexing for Spotlight, or running code for a time-critical user task, code is run across any of the available cores. In an Apple silicon chip like those in the M4 family, background tasks are normally constrained to efficiency (E) cores, leaving the performance (P) cores for your apps and other pressing user tasks. This brings significant energy economy for background tasks, and keeps your Mac more responsive to your demands.

Some tasks are normally constrained to run only on E cores. These include scheduled background tasks like Spotlight indexing, Time Machine backups, and some encoding of media. Game Mode is perhaps a more surprising E core user, as explained below.

Most user tasks are run preferentially on P cores, when they’re available. When there are more high-priority threads to be run than there are available P cores, then macOS will normally send them to be run on E cores instead. This also applies to threads running a Virtual Machine (VM) using lightweight virtualisation, whose threads will be preferentially scheduled on P cores when they’re available, even when code being run in the VM would normally be allocated to E cores.

macOS also controls the clock speed or frequency of cores. For background tasks running on E cores, their frequency is normally held relatively low, for best energy efficiency. When high-priority threads overspill onto E cores, they’re normally run at higher frequency, which is less energy-efficient but brings their performance closer to that of a P core. macOS goes to great lengths to schedule threads and control core frequencies to strike the best balance between energy efficiency and performance.

Unfortunately, it’s normally hard to see effects of frequency in apps like Activity Monitor. Its CPU % figures only show the percentage of cycles that are used for processing, and make no allowance for core frequency. It will therefore show a background thread running at low frequency but 100%, the same as a thread overspilt from P cores running at the maximum frequency of that E core. So when you see Spotlight indexing apparently taking 200% of CPU % on your Mac’s E cores, that might only be a small fraction of their maximum capacity if they were running at maximum frequency.

There are no differences between chips in the M4 family when it comes to each type of CPU core: each P core in a Base variant is the same as each in an M4 Pro or Max, with the same maximum frequency, and the same applies to E cores. macOS also allocates threads to different types of core using the same rules, and their frequencies are controlled the same as well. What differs between them is the number of each type of core, ranging from 4 P and 4 E in the 8-core variant of the Base M4, up to 12 P and 4 E in the 16-core variant of the M4 Max. Thus, their single-core benchmark results should be almost identical, although their multi-core results should vary according to the number of cores.

Game Mode

This mode is an exception to normal CPU and GPU core use, as it:

• gives preferential access to the E cores,
• gives highest priority access to the GPU,
• uses low-latency Bluetooth modes for input controllers and audio output.

However, my previous testing didn’t demonstrate that apps running in Game Mode were given exclusive access to E cores. But for gamers, it now appears that the more E cores, the better.

GPU cores

These are also used for tasks other than graphics, such as some of the more demanding calculations required for Machine Learning and AI. However, experience so far with Writing Tools in Sequoia 15.1 is that macOS currently offloads their heavy lifting to be run off-device in one of Apple’s dedicated servers. Although having plenty of GPU cores might well be valuable for non-graphics purposes in the future, for now there seems little advantage for many.

Thunderbolt 5

M4 Pro and Max, but not Base variants, come equipped with Thunderbolt ports that not only support Thunderbolt 3 and 4, but 5, as well as USB4. Thunderbolt 5 should effectively double the speed of connected TB5 SSDs, but to see that benefit, you’ll need to buy a TB5 SSD. Not only are they more expensive than TB3/4 models, but at present I know of only one range that’s due to ship this year. There will also be other peripherals with TB5 support, including at least one dock and one hub, although neither is available yet. The only TB5 accessories that are already available are cables, and even they are expensive.

TB5 also brings increased video bandwidth and support for DisplayPort 2.1, although even the M4 Max can’t make full use of that. If you’re looking to drive a combination of high-res displays, consult Apple’s Tech Specs carefully, as they’re complicated.

Although TB5 will become increasingly important over the next few years, TB3/4 and USB4 are far from dead yet and are supported by all M4 models.

Which M4 chip?

The table below summarises key figures for each of the variants in the M4 family that have now been released. It’s likely that next year Apple will release an Ultra, consisting of two M4 Max chips joined in tandem, in case you feel the burning desire for 24 P and 8 E cores.

Models available next week featuring each M4 chip are shown with green rectangles at the right.

There are two variants of the Base M4, one with 4P + 4E and 8 GPU cores, the same as Base variants in M1 to M3 families. There’s also the more capable variant, for the first time with 4P + 6E, which promises to be a better all-rounder, and when in Game Mode. It also has an extra couple of GPU cores.

The M4 Pro also comes in two variants, this time differing in the number of P cores, 8 or 10, and GPU cores, 16 or 20. Those overlap with the M4 Max, with 10 or 12 P cores and 32 or 40 GPU cores. Thus the gap between M4 Pro and Max isn’t as great as in the M3, with the GPUs in the M4 Max being aimed more at those working with high-res video, for instance. For more general use, there’s little difference between the 14-core Pro and Max.

Memory and storage

Chips in the M4 family also determine the maximum memory and internal SSD capacity. Apple has at last eliminated base models with only 8 GB of memory, and all now start with at least 16 GB. Base M4 chips are limited to a maximum of 32 GB, while the M4 Pro can go up to 64 GB, and the 16-core Max up to 128 GB, although in its 14-core variant, the Max is only available with 36 GB (I’m very grateful to Thomas for pointing this out below).

Unfortunately, Apple hasn’t increased the minimum size of internal SSD, which remains at 256 GB for some base models. Smaller SSDs may be cheaper, but they are also likely to have shorter lives, as under heavy use their small number of blocks will be erased for reuse more frequently. That may shorten their life expectancy to much less than the normal period of up to 10 years, as was seen in some of the first M1 models. This is more likely to occur when swap space is regularly used for virtual memory. I for one would have preferred 512 GB as a starting point.

While Base M4 chips come with SSDs up to 2 TB in size, both Pro and Max can be supplied with internal SSDs of up to 8 TB.

I hope this proves useful in guiding your decision.

Almost exactly a year after it released its first Macs featuring chips in the M3 family, Apple has replaced those with the first M4 models. Benchmarkers and core-counters are now busy trying to understand how these will change our Macs over the coming year or so. Before I reveal which model I have ordered, I’ll try to explain how these change the Mac landscape, concentrating primarily on CPU performance.

CPU cores

CPUs in the first two families, M1 and M2, came in two main designs, a Base variant with 4 Performance and 4 Efficiency cores, and a Pro/Max with 8 P and 2 or 4 E cores, that was doubled-up to make the Ultra something of a beast with its 16 P and 4 or 8 E cores. Last year Apple introduced three designs: the M3 Base has the same 4 P and 4 E CPU core configuration as in the M1 and M2 before it, but its Pro and Max variants are more distinct, with 6 P and 6 E in the Pro, and 10-12 P and 4 E cores in the Max. The M4 family changes this again, improving the Base and bringing the Pro and Max variants closer again.

As these are complicated by sub-variants and binned versions, I have brought the details together in a table.

I have set the core frequencies of the M4 in italics, as I have yet to confirm them, and there’s some confusion whether the maximum frequency of the P core is 4.3 or 4.4 GHz.

Each family of CPU cores has successively improved in-core performance, but the greatest changes are the result of increasing maximum core frequencies and core numbers. One crude but practical way to compare them is to total the maximum core frequencies in GHz for all the cores. Strictly speaking, this should take into account differences in processing units between P and E cores, but that also appears to have changed with each family, and is hard to compare. In the table, columns giving Σfn are therefore simply calculated as
(max P core frequency x P core count) + (max E core frequency x E core count)

Plotting those sum core frequencies by variant for each of the four families provides some interesting insights.

Here, each bar represents the sum core frequency of each full-spec variant. Those are grouped by the variant type (Base, Pro, Max, Ultra), and within those in family order (M1 purple, M2 pale blue, M3 dark blue, M4 red). Many trends are obvious, from the relatively low performance expected of the M1 family, except the Ultra, and the changes between families, for example the marked differences in the M4 Pro, and the M3 Max, against their immediate predecessors.

Sum core frequencies fall into three classes: 20-30, 35-45, and greater than 55 GHz. Three of the four chips in the M1 family are in the lowest of those, with only the M1 Ultra reaching the highest. The M4 is the first Base variant to reach the middle class, thanks in part to its additional two E cores. Two of the M4 variants (Pro and Max) have already reached the highest class, and any M4 Ultra would reach far above the top of the chart at 128 GHz.

Real-world performance will inevitably differ, and vary according to benchmark and app used for comparison. Although single-core performance has improved steadily, apps that only run in a single thread and can’t take advantage of multiple cores are likely to show little if any difference between variants in each family.

Game Mode is also of interest for those considering the two versions of the M4 Base, with 4 or 6 E cores. This is because that mode dedicates the E cores, together with the GPU, to the game being played. It’s likely that games that are more CPU-bound will perform significantly better on the six E cores of the 10-Core version of the iMac, which also comes with a 10-core GPU and four Thunderbolt 4 ports.

Memory and GPU

Memory bandwidth is also important, although for most apps we should assume that Apple’s engineers match that with likely demand from CPU, GPU, neural engine, and other parts of the chip. There will always be some threads that are more memory-bound, whose performance will be more dependant on memory bandwidth than CPU or GPU cores.

Although Apple claims successive improvements in GPU performance, the range in GPU cores has started at 8 and attained 32-40 in Max chips. Where the Max variants come into their own is support for multiple high-res displays, and challenging video editing and processing.

Thunderbolt and USB 3

The other big difference in these Macs is support for the new Thunderbolt 5 standard, available only in models with M4 Pro or M4 Max chips; Base variants still only support Thunderbolt 4. Although there are currently almost no Thunderbolt 5 peripherals available apart from an abundant supply of expensive cables, by the end of this year there should be at least one range of SSDs and one dock shipping.

As ever with claimed Thunderbolt performance, figures given don’t tell the whole story. Although both TB4 and USB4 claim ‘up to’ 40 Gb/s transfer rates, in practice external SSD performance is significantly different, with Thunderbolt topping out at about 3 GB/s and USB4 reaching up to 3.4 GB/s. In practice, TB5 won’t deliver the whole of its claimed maximum of 120 Gb/s to a single storage device, and current reports are that will only achieve disk transfers at 6 GB/s, or twice TB4. However, in use that’s close to the expected performance of internal SSDs in Apple silicon Macs, and should make booting from a TB5 external SSD almost indistinguishable in terms of speed.

As far as external ports go, this widens the gap between the M4 Pro Mac mini’s three TB5 ports, which should now deliver 3.4 GB/s over USB4 or 6 GB/s over TB5, and its two USB-C ports that are still restricted to USB 3.2 Gen 2 at 10 Gb/s, equating to 1 GB/s, the same as in M1 models from four years ago.

My choice

With a couple of T2 Macs and a MacBook Pro M3 Pro, I’ve been looking to replace my original Mac Studio M1 Max. As it looks likely that an M4 version of the Studio won’t be announced until well into next year, I’m taking the opportunity to shrink its already modest size to that of a new Mac mini. What better choice than an M4 Pro with 10 P and 4 E cores and a 20-core GPU, and the optional 10 Gb Ethernet? I seldom use the fourth Thunderbolt port on the Studio, and have already ordered a Kensington dock to deliver three TB5 ports from one on the Mac, and I’m sure it will drive my Studio Display every bit as well as the Studio has done.

If you have also been tempted by one of the new Mac minis, I was astonished to discover that three-year AppleCare+ for it costs less than £100, that’s two-thirds of the price that I pay each year for AppleCare+ on my MacBook Pro.

I look forward to diving deep into both my new Mac and Thunderbolt 5 in the coming weeks.

External storage is invariably sold with ‘up-to’ performance figures. In practice, you’ll seldom realise anything like some write or read speeds claimed. And when it comes to prolonged tasks like that first full Time Machine backup, no matter how fast you thought that drive would be, it always takes longer than expected.

Over the last few years I have tested and reviewed many examples of different types of external storage, from basic USB 3 hard drives, to the latest USB4 SSD enclosures, and NAS packed with fast SSDs. This article draws on all those test results to give you a better idea of what to expect when they’re being used with your Mac.

Results quoted here are typical for those tests performed mostly using a Mac Studio M1 Max, but unless otherwise indicated should be similar for recent Intel models. They’re summarised in this table.

Write speeds are given for:

• the single 50 MB write test performed by Time Machine before each backup;
• 500 multiple concurrent writes of 4 KB each, performed in those same Time Machine tests;
• calculated net write speed over a first full backup to APFS of at least 400 GB;
• general write speed measurement using my app Stibium, which gives broadly similar results to other leading benchmarking apps.

General read speeds are also obtained using Stibium, and similar to other apps. All speeds are given as MB/s for consistency.

Before looking at individual types of storage, one obvious and important result is the effect of throttling by macOS on Time Machine backup performance. Considering Time Machine’s own tests, writing a single 50 MB file is performed consistently at around 200-225 MB/s to local storage of whatever type, and multiple concurrent writes of 4 KB files reach around 20-23 MB/s regardless of local storage type. Those hold good even when you back up to a fast Thunderbolt 3 SSD, and backing up to a NAS is little quicker unless it’s over 2.5GbE to an NVMe SSD. Local transfer speeds only differ more substantially in general tests, when they aren’t throttled as they are in Time Machine.

Hard disks

When writing to or reading from a local hard disk, performance varies substantially according to which sectors on the hard disk are being accessed. This is a well-known phenomenon, and the result of geometry, as sectors are faster at the periphery of the disk’s platter, and slower in the inner part. Ranges given here take that into account: the lower figure is for inner sectors, and the higher for outer ones. Some users compensate for this effect, and only ever use the outer half of a disk’s sectors to obtain better performance, but that reduces their available capacity, and effectively doubles their cost per TB.

SSDs

SATA SSDs may be cheapest, but they’re also slowest, and with Macs they generally don’t enjoy Trim or SMART health indicator support. Of the two, Trim support is usually the more important, as without that, they can accumulate blocks waiting to be erased and returned for further use, and as a result their write (but not read) speed can fall as low as 100 MB/s. Unless used for largely static storage, this is a significant risk.

NVMe SSDs deliver twice the performance of SATA models, and generally enjoy Trim but not SMART indicator support. This makes them far better suited to general use, as their write speeds should be sustained from new throughout their working life.

USB 3.2 Gen 2, Thunderbolt 3, USB4

Translating commonly quoted transfer speeds for these three protocols into real-world speeds turns out to be complex. In practice, these are what you can expect to see:

• USB 3.2 Gen 2 at 10 Gb/s is slightly less than 1 GB/s
• Thunderbolt 3 at 32 Gb/s is up to 3 GB/s
• USB4 at 40 Gb/s is up to 3.4 GB/s.

All recent models of Mac, both Intel and Apple silicon, should realise full performance over USB 3.2 Gen 2 and Thunderbolt 3, but support for USB4 is limited to Apple silicon. Unless a drive or enclosure specifically includes Thunderbolt 3 as a fallback, when connected to an Intel Mac, you should expect it to fall back to USB 3.2 Gen 2 at just under 1 GB/s, less than a third of the speed of USB4.

NAS

Although I haven’t made any systematic comparison between AFP and SMB network protocols, I can see no consistent difference in their performance, when used with the latest versions of macOS and NAS software. The latter, though, can be critical: older versions of NAS software can perform poorly when used over SMB with recent macOS. Keeping your NAS software up to date is important.

Throttling of Time Machine backup writing isn’t supposed to occur when backing up over a network, and there is some evidence here to support that, with significantly better results for 50 MB test files. However, those are only apparent when using NVMe SSDs in the NAS, with a wired Ethernet 2.5GbE connection to provide sufficient bandwidth.

Check TM performance

Provided that your Mac is running a recent version of macOS and backing up to APFS, it’s simple to read the two write performance tests that occur at the start of each Time Machine backup using my free T2M2. Alternatively, you can also read them using the Time Machine custom log extract in Mints. In T2M2 they should look something like:
Destination IO performance measured:
Wrote 1 50 MB file at 238.02 MB/s to "/Volumes/ThunderBay2" in 0.210 seconds
Concurrently wrote 500 4 KB files at 35.58 MB/s to "/Volumes/ThunderBay2" in 0.058 seconds

Check general performance

Although there are other apps that will do this, I developed Stibium for this purpose. Follow the ‘gold standard’ procedure detailed in its Help Reference to obtain the most accurate and reproducible results. Stibium can test any storage you can access in the Finder, including all local devices and networked systems such as NAS.

Further reading

Which external drives have Trim and SMART support?
How to evaluate an external SSD
You can read my reviews in MacFormat and MacLife magazines, available in the App Store.