Macs have undergone three major hardware architectural transitions over the last 41 years, and it may well be that this year sees the completion of the last of those. I’ve previously given a brief account of those changes in CPUs; this article summarises when and how those transitions have taken place.

Classic Macs used Motorola’s 68K series of processors until the Spring of 1994, when the first transition to PowerPC processors started.

PowerPC 1994-98

Apple had originally intended to launch its new range of Power Macs on the tenth birthday of the Mac in January 1994, but its first three models, the 6100, 7100 and 8100, weren’t ready until March, when they came with System 7.1.2 and a PowerPC ‘enabler’. Much of the system was still in 68K code, so to enable its continuing use, and to allow the running of existing 68K apps, it came with a built-in 68K emulator. That was surprisingly mature, as it had first been developed by Gary Davidian for use in experimental RISC-based Macs during 1990, as part of the Cognac project to identify a successor for the 68K.

Mac OS supported both PowerPC and 68K architectures from March 1994 to Mac OS 8.1 in January 1998. Support was dropped from 8.5 in October of that year, although the 68K emulator remained until the final version of Classic Mac OS, 9.2.2, released in December 2001. The last 68K Macs were the LC 580, produced between April 1995 and April 1996, and the PowerBook 190cs, discontinued in October 1996.

Thus, the transition period to PowerPC processors lasted from March 1994 to October 1998, a period of 4.5 years.

Apple System Profiler here shows details of a Power Mac G3 Blue and White from 1999.

TattleTech reveals that it was the first model to be officially assigned a name in the new series, as a PowerMac1,1, or 406 in the old Machine ID numbering.

Running a Windows PC in emulation using VirtualPC, seen here in July 1999, was useful but hardly performant.

PowerPC processors reigned for just over a decade before Apple switched a second time, to Intel CPUs.

Intel 2006-09

Moving to a well-established architecture was anticipated to be quicker, and when Apple announced the change at WWDC in 2005, Steve Jobs expected the hardware transition to start by June 2006, and to be completed by early 2008. In fact, the first Intel Macs shipped in January and February 2006, the iMac and Mac mini respectively. The last Power Mac G5 was produced between October 2005 and August 2006, and by the end of that year the full range of Intel Macs was complete.

Mac OS X came with initial Intel support in 10.4.4, installed on the first iMacs. The last version to run on PowerPC processors was 10.5.8 in August 2009, and in the same month Mac OS X 10.6 was Intel-only.

Rather than opting for another software emulator to run PowerPC code on Intel processors, Apple licensed code translation technology named QuickTransit from Transitive Corporation, an extension of Dynamite technology developed by the University of Manchester, England. This version of Rosetta could translate G3, G4 and AltiVec instructions, but not those specific to the PowerPC G5 processor. This was bundled in Mac OS X from 10.4.4 in January 2006, until it was discontinued in 10.6.8 in July 2011.

The transition period to Intel processors lasted from January 2006 to August 2009, a period of just over 3.5 years.

Apple silicon 2020-?

Apple’s third transition has been distinguished by its lengthy and staged preparation, and the fact that its goal was the first Mac that has been completely designed and developed by Apple. Its roots go back to a partnership with the British microcomputer manufacturer Acorn Computers in the 1980s that led to the development of the Acorn RISC Machine using an early RISC processor, and the origin of the name ARM. During the 1990s Apple, through Larry Tesler, was a major investor in ARM, who provided the processor for Apple’s Newton handheld devices launched in 1993. Although the Newton was a commercial failure, it was the germ for the first iPhone in 2007, and the iPad three years later.

Another landmark in the preparations for Apple silicon Macs was the incorporation of the T2 Arm-based ‘security chip’ in Intel Macs from December 2017 onwards, although Apple didn’t incorporate that into a regular iMac model until as late as 2020.

Apple announced this transition at WWDC in June 2020, and the first Apple silicon Macs shipped in November that year, Mac mini, MacBook Pro and MacBook Air models. This was less than a year after the release of the last Intel Mac, the delayed Mac Pro of December 2019, which continued in production until June 2023, and the more popular 27-inch iMac made between August 2020 and March 2022. First Apple silicon Macs came with macOS 11.0, and both architectures remain supported as far as macOS 15 Sequoia, from 2024.

To enable its new Macs to run apps built for Intel x86 processors, Apple returned to code translation in Rosetta 2, bundled in macOS 11 and later, but downloaded and updated separately. To accelerate the launching of x86-64 apps, this uses both ‘just-in-time’ translation at the time of launch, and ahead-of-time (AOT) when an x86-64 single-architecture binary is installed. In contrast to its earlier emulator and even the first version of Rosetta, this performs spectacularly well.

The transition to Apple silicon thus started in November 2020, and appears likely to end with the release of macOS 16 in the autumn/fall of 2025. That would be a period of almost 5 years, even longer than the first transition to PowerPC. This time we’re better prepared for the future, as Apple silicon Macs offer excellent virtualisation of macOS, allowing the latest chips to run macOS as old as Monterey from 2021, together with full support for x86-64 apps using Rosetta 2 in the virtual machine.

Further reading

The PowerPC Triumph, 1997-98, by Andy F Mesa
Mac 68K Emulator on Wikipedia
Rosetta on Wikipedia
Transition to Intel on Wikipedia
Transition to Apple silicon on Wikipedia

From the outset, the Macintosh was a single integrated unit, at a time when other personal computers came with separate displays.

It took three years for Macs to diverge into the all-in-one SE and the modular Macintosh II with its conventional case and separate colour monitor. The meteoric rise of desktop publishing demanded large, deep and heavy cathode-ray tube (CRT) colour displays that only came separately, and needed long graphics cards that had to be fitted inside the computer’s chassis.

Although the Mac SE weighed up to almost 10 kg (22 pounds), many lugged them around in soft cases slung over their shoulders, providing a degree of portability. There are some folk whose backs still bear witness to those days of the luggable Mac.

Integral CRT displays hardly changed over this period. The Macintosh 128K came with a 9 inch screen displaying a mere 512 x 342 pixels in monochrome. Ten years later, the Color Classic was the first all-in-one to come with a 10 inch colour screen, and that only increased resolution to 512 x 384 pixels. Neither was there any support for external displays, until the LC 520 in July 1993, with its 14 inch colour CRT at 640 x 480 resolution and display port.

During the 1990s, Apple offered various Power Macintosh, Performa and LC all-in-one models featuring integral or piggybacked displays, culminating in the Power Macintosh 5500 in 1997, with its 15 inch CRT of which less than 13 inches were viewable, and supporting up to 832 x 624 pixels.

Apple’s next innovative all-in-one was the Twentieth Anniversary Macintosh (TAM), released a year late in 1997. It came with a 12.1 inch backlit active-matrix screen rather than the traditional CRT, in this unique design. Although a limited edition intended to be a collector’s item, it was overpriced and sold poorly, and has since been eclipsed by the most innovative model since the original 128K.

In May 1998, Apple announced the first iMac, based on a PowerPC G3 processor and a 15 inch CRT, of which 13.8 inches are viewable at resolutions of up to 1024 x 768 pixels. The design wrapped the case around the bulk of the display in the form of a ‘gumdrop’, using coloured translucent plastic later offered in a range of bright colours.

It was also technically innovative, featuring novel USB ports and discarding the traditional floppy disk drive in favour of optical and hard drives. This shipped in August 1998, with hardware revisions that October and the following January.

A few months later Apple quietly slipped out the Power Macintosh G3 All-in-One, but that proved to be a dead-end and has been largely forgotten in favour of the iconic iMac.

By January 2002, flat-panel displays were starting to displace bulky CRTs, and Apple made use of them in its first flat-panel iMac. This featured a PowerPC G4 processor, and a 15 inch TFT active-matrix LCD delivering up to 1024 x 768 pixels. The computer components were assembled into a heavy hemispherical base on which the display was mounted using a hinged stainless steel arm resembling an Anglepoise desk lamp, which had been designed in 1932 by George Carwardine and is still in production.

This ‘Anglepoise’ mount remains the best adjustable mechanism used with a display, ensured effortless positioning to suit each user, and eventually supported 20 inch flat-panel displays.

With displays now thin enough to allow computer components to be integrated behind the screen, the next step was to eliminate the heavy base. Apple achieved that in August 2004 with the iMac G5, in its 17 and 20 inch models. With the switch to Intel processors and further integration in computer components, display size rose to 24 inches in 2007, and 27 inches two years later.

For many, the zenith of the iMac came in Retina 5K displays first offered in 2014, and the most powerful Intel iMac of all, the 27 inch iMac Pro released at the end of 2017. The latter features Intel Xeon processors with 8 or 10 cores together with the new T2 security chip. Although it doesn’t appear to have sold well, it was popular with developers and others during the hiatus between the Mac Pro models of 2013 and 2019.

Although the iMac Pro was the first Mac to feature a T2 chip, their inclusion in other iMacs was delayed until Apple had already announced its move to Apple silicon models. The last Intel iMac with a 27 inch Retina 5K display was released in August 2020, three months before Apple shipped the first M1 Mac mini and others.

Since May 2021, Apple has offered a succession of three iMacs powered by its M-series chips, all with a 24 inch Retina 4.5K display. They follow in the line of the original iMac from 1998, and come in a range of colours. But there are many who are still clinging onto ageing Intel iMacs in the hope that, one day, Apple will offer an all-in-one in the spirit of the iMac Pro, with a Pro grade chip and a 27 inch Retina 5K display.

Recent updates to macOS Sequoia 15.4, Sonoma 14.7.5 and Ventura 13.7.5 brought firmware updates for some Macs, but not others. As I have now analysed those, and they’re reflected in the databases accessed by SilentKnight, and in my reference articles here (listed at the end), this article explains which are still being maintained by Apple.

Intel Macs without T2 chips

There are only two models of Mac without a T2 or Apple silicon chip whose firmware is still supported for updates: the iMac19,1 and 19,2, respectively the 2019 Retina 5K 27-inch and Retina 4K 21.5-inch. In this round of updates, they moved up to an EFI version of 2075.100.3.0.3, dated as recently as 3 March 2025. As they can run Sequoia, they’re expected to have continuing macOS security updates until at least the summer of 2027.

Older models of iMacs, MacBook Pros, and a single MacBook, remain with EFI firmware that was last updated in June 2024, and is unlikely ever to be updated any further. macOS support for them is expected to end when security updates for Ventura are discontinued at the end of the summer this year.

T2 Macs

For the 20 days between the release of 15.3.2 and 15.4, Intel Macs with T2 chips that were running Sequoia had a slightly more recent release of iBridge firmware. In 15.3.1, 14.7.4 and 13.7.4, that was 22.16.13051.0.0,0, but 15.3.2 brought version 22.16.13060.0.0,0. This is one of very few occasions in which T2 Macs running supported versions of macOS have had different firmware versions installed.

Thankfully, this last round of updates has rectified that, and all Macs with T2 chips should now be running 2075.101.2.0.0 (iBridge 22.16.14248.0.0,0). This is encouraging, not only for simplicity, but because it demonstrates that Apple is continuing to support not only the ‘Bridge’ Arm chip, but EFI as well. How much longer that will continue depends on whether there is Intel support in macOS 16, expected to be announced at WWDC in early June, and released in September or October this year.

At a minimum, macOS support for T2 Macs should last at least until summer 2027, and that should be extended to the following year if macOS 16 comes with Intel support.

Apple silicon Macs

All Apple silicon Macs should now be using iBoot version 11881.101.1, which was installed with these updates. The most recent MacBook Air and Mac Studio models with M4 family (or M3 Ultra) chips had their own update to 15.3.2, but 15.4 covers all current models in the single distribution, with the same firmware version.

There’s a growing number of reports of Apple silicon Macs experiencing problems updating to Sequoia 15.4, either on their internal SSD or on bootable external disks. This seems most likely in models with M1 family chips, and suggests that changes made in the installer might be responsible. As this doesn’t appear to affect 14.7.5 or 13.7.5 updates, it’s unlikely to lie in the firmware. There are several strategies you can adopt to work around this, including:

• Try updating in Safe mode. This is a longstanding function of Safe mode, described here.
• Start up in the correct paired Recovery system, and install Sequoia there. This should be attempted conservatively, without creating a fresh Data volume, but you must ensure that you have at least one complete backup ready in case anything goes wrong and the whole boot volume group has to be replaced.

Provided the Mac is already running at Full Security, there shouldn’t be any value in changing that. Performing a full Restore in DFU Mode isn’t as daunting as it might seem, but is a drastic solution requiring a recent second Mac, and full restore from your backup. If you’re getting to that stage, contact Apple Support who hopefully will now be only too familiar with these problems.

Summary

• Intel Macs without T2 chips: iMac19,1 and 19,2: EFI 2075.100.3.0.3; no change in other models.
• Intel Macs with T2 chips: 2075.101.2.0.0 (iBridge 22.16.14248.0.0,0).
• Apple silicon Macs: 11881.101.1.

Reference data

Which firmware should your Mac be using? (version 9, Sequoia)
Which firmware should your Mac be using? (version 8) – for Sonoma
Which firmware should your Mac be using? (version 7) – for Ventura

Last week’s security updates to macOS have left some confusion over version numbers, and firmware for T2 Macs. This article attempts to clarify what happened, and where supported versions of macOS are going next.

Security updates 11 March 2025

Apple released:

• macOS 15.3.2 Sequoia
• Safari for macOS 14.7.4 Sonoma
• Safari for macOS 13.7.4 Ventura.

There were no security updates for Sonoma or Ventura other than their Safari updates.

There was also a firmware update included in the 15.3.2 update, changing the version of iBridge firmware in the T2 chip of Intel Macs from 22.16.13051.0.0,0 to 22.16.13060.0.0,0. There were no firmware updates for Apple silicon Macs, nor for Intel models without T2 chips, I understand.

Sequoia

If your Mac is running macOS Sequoia and has been updated, it should now be running 15.3.2 (build 24D81). If it has a T2 chip, it should have updated its firmware to read
EFI 2069.80.3.0.0 (iBridge: 22.16.13060.0.0,0)

Safari should be version 18.3.1 (20620.2.4.11.6).

Sonoma

If your Mac is running macOS Sonoma and has been updated, it should still be running 14.7.4 (build 23H420). If it has a T2 chip, its firmware should remain at
EFI 2069.80.3.0.0 (iBridge 22.16.13051.0.0,0)

Safari should have been updated to version 18.3.1 or 18.4 (19621.1.14.11.3, 19621).

Ventura

If your Mac is running macOS Ventura and has been updated, it should still be running 13.7.4 (build 22H420). If it has a T2 chip, its firmware should remain at
EFI 2069.80.3.0.0 (iBridge 22.16.13051.0.0,0)

Safari should have been updated to version 18.3.1 or 18.4 (18621.1.14.11.3, 18621).

SilentKnight

To keep a complex situation as simple as possible, SilentKnight only considers one firmware version to be current for each model of Mac. If it tried anything more complex, I’d not be able to cope. As there are presently two different ‘current’ and supported versions of T2 firmware in use, SilentKnight goes with the older one. That way it doesn’t complain, but politely remarks for Sequoia 15.3.2:
EFI version found 2069.80.3.0.0 (iBridge: 22.16.13060.0.0,0) ;
expected 2069.80.3.0.0 (iBridge 22.16.13051.0.0,0)

Please bear with me until Apple resyncs T2 firmware across the three supported versions of macOS. I’m sure that will return with the release of 15.4, 14.7.5 and 13.7.5. If not, we can all scream together.

Sonoma 14.7.5 and Ventura 13.7.5

Many have been reporting that their Macs have been updated to 14.7.5 or 13.7.5, and some have claimed that those versions have been released by Apple. They are in fact beta-releases of the next scheduled updates to Sonoma and Ventura, and haven’t yet been generally released. If your Mac is running one of those, you might like to check it against recent beta-releases:

• 21 February 2025 betas: Sonoma 14.7.5 (23H510), Ventura 13.7.5 (22H510)
• 10 March 2025 betas: Sonoma 14.7.5 (23H520), Ventura 13.7.5 (22H520)
• 17 March 2025 betas: Sonoma 14.7.5 (23H525), Ventura 13.7.5 (22H525)

App Store full installers

If you download a full installer from the App Store or elsewhere, the current releases are:

• Sequoia 15.3.2 (build 24D81)
• Sonoma 14.7.4 (build 23H420), which will then need Safari updated
• Ventura 13.7.4 (build 22H420), which will then need Safari updated.

How has this happened?

Normally, when the current version of macOS has a security update, the two older versions that are still supported have matching security updates. That would have brought 14.7.5 and 13.7.5 along with 15.3.2. However, in this case the patch to be applied could be supplied in a Safari update for the older two. As that’s much smaller and simpler than a full macOS update, Apple opted to supply those as Safari updates alone, which can’t of course be a new version of macOS.

This is possible because Safari and some of its supporting frameworks and components aren’t part of the Signed System Volume, so updating them doesn’t require the System volume to be rebuilt, turned into a snapshot, and installed as a new Signed System Volume.

However, firmware updates can only be supplied and installed as part of a full macOS update, so it was only possible to update T2 firmware in Sequoia systems being updated the long way to 15.3.2.

I hope this dispels any remaining confusion.

I’m grateful to ExcleX for pointing out that Safari versions can vary according to when you updated.