Arrival of Linux 6.15 hails end of 486-class CPUs
(2025/05/28)
- Reference: 1748453593
- News link: https://www.theregister.co.uk/2025/05/28/kernel_615_arrives/
- Source link:
Over the holiday weekend, Linus Torvalds released the latest Linux kernel – signalling the end of the line for 486-class chips.
Torvalds [1]announced kernel 6.15 on Sunday, after a short last-minute delay. Relative to [2]March's kernel 6.14 release , there were a lot of code changes in this release, but most of them are not big-bang changes. [3]Linux Weekly News's analysis said:
The 6.14 kernel development cycle only brought in 11,003 non-merge changesets, making it the slowest cycle since 4.0, which was released in 2015. The 6.15 kernel, instead, brought in 14,612 changesets, making it the busiest release since 6.7, released at the beginning of 2024. The kernel development process, in other words, is back up to full speed.
As we said back at the start of this month, the change that arguably sounds like the biggest news probably isn't: this release [4]drops support for x86 CPUs before the Intel Pentium . There are a handful of companies still making 486-class CPUs for embedded computers, but those tend not to run the latest Linux kernel, or indeed, Linux at all.
Effectively, the kernel now only supports i586 and above. It also won't allow more than eight x86-32 CPUs in one machine, and [5]removes 32-bit PAE support – so even on high-end x86-32 boxes, Linux 6.15 and above can't access more than 4GB of RAM.
The few Linux distros that still offer x86-32 support often supply i686-optimized code, meaning it's aimed at the Pentium Pro (codenamed P6) or above. We suspect the kernel may follow suit before all that long. We do wonder how soon the kernel itself will drop 32-bit support completely. Ubuntu dropped x86-32 support in [6]version 19.10 "Eoan Ermine" , and Debian is [7]set to do so next release .
[8]Three ways to run Windows apps on a Linux box
[9]Torvalds' typing taste test touches tactile tragedy
[10]The elusive goal of Unix – or Linux – simplicity
[11]The 'End of 10' is nigh, but don't bury your PC just yet
[12]The State of Open Source in 2025? Honestly, it's a mess but you knew that already
The single largest contributor of changes to 6.15 was Kent Overstreet, who continues to work on improving his bcachefs filesystem. This does seem to be reaching a useful level now, as the recent Reddit discussion on [13]the current maturity level of bcachefs suggests.
Alongside improvements to bcachefs, there are also ones to Btrfs, XFS, Ext4 and the Flash-specific F2FS. Rust support has improved, now including on ARMv7. For an exhaustive deep-dive into the changes, LWN examines what's changed, across [14]part 1 and [15]part 2 .
[16]
As is generally the case, shortly after the mainstream kernel is released, the [17]Linux-libre project released its corresponding version, [18]linux-libre 6.15-gnu , which removes all proprietary drivers and code from the kernel, for a 100 percent GNU Free Software kernel. ®
Get our [19]Tech Resources
[1] https://lkml.org/lkml/2025/5/25/345
[2] https://www.theregister.com/2025/03/25/linux_6_14_day_late/
[3] https://lwn.net/Articles/1022414/
[4] https://www.theregister.com/2025/05/07/linux_kernel_drops_486/
[5] https://web.git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/cpu&id=bbeb69ce301323e84f1677484eb8e4cd8fb1f9f8
[6] https://www.theregister.com/2019/10/17/canonical_releases_ubuntu_1910_eoan_ermine/
[7] https://www.theregister.com/2023/12/19/debian_to_drop_x86_32/
[8] https://www.theregister.com/2025/05/28/three_ways_to_win_on_lin/
[9] https://www.theregister.com/2025/05/20/torvalds_typing_taste_test_touches/
[10] https://www.theregister.com/2025/05/27/elusive_goal_of_simplicity/
[11] https://www.theregister.com/2025/05/15/end_of_10_campaign/
[12] https://www.theregister.com/2025/04/29/state_of_open_source/
[13] https://old.reddit.com/r/bcachefs/comments/1kwh9w8/the_current_maturity_level_of_bcachefs/
[14] https://lwn.net/Articles/1015414/
[15] https://lwn.net/Articles/1016119/
[16] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_software/oses&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=2&c=2aDeHdvzqMKv2VkZm9X0NtQAAAdg&t=ct%3Dns%26unitnum%3D2%26raptor%3Dcondor%26pos%3Dtop%26test%3D0
[17] https://www.fsfla.org/ikiwiki/selibre/linux-libre/
[18] https://www.fsfla.org/pipermail/linux-libre/2025-May/003589.html
[19] https://whitepapers.theregister.com/
Torvalds [1]announced kernel 6.15 on Sunday, after a short last-minute delay. Relative to [2]March's kernel 6.14 release , there were a lot of code changes in this release, but most of them are not big-bang changes. [3]Linux Weekly News's analysis said:
The 6.14 kernel development cycle only brought in 11,003 non-merge changesets, making it the slowest cycle since 4.0, which was released in 2015. The 6.15 kernel, instead, brought in 14,612 changesets, making it the busiest release since 6.7, released at the beginning of 2024. The kernel development process, in other words, is back up to full speed.
As we said back at the start of this month, the change that arguably sounds like the biggest news probably isn't: this release [4]drops support for x86 CPUs before the Intel Pentium . There are a handful of companies still making 486-class CPUs for embedded computers, but those tend not to run the latest Linux kernel, or indeed, Linux at all.
Effectively, the kernel now only supports i586 and above. It also won't allow more than eight x86-32 CPUs in one machine, and [5]removes 32-bit PAE support – so even on high-end x86-32 boxes, Linux 6.15 and above can't access more than 4GB of RAM.
The few Linux distros that still offer x86-32 support often supply i686-optimized code, meaning it's aimed at the Pentium Pro (codenamed P6) or above. We suspect the kernel may follow suit before all that long. We do wonder how soon the kernel itself will drop 32-bit support completely. Ubuntu dropped x86-32 support in [6]version 19.10 "Eoan Ermine" , and Debian is [7]set to do so next release .
[8]Three ways to run Windows apps on a Linux box
[9]Torvalds' typing taste test touches tactile tragedy
[10]The elusive goal of Unix – or Linux – simplicity
[11]The 'End of 10' is nigh, but don't bury your PC just yet
[12]The State of Open Source in 2025? Honestly, it's a mess but you knew that already
The single largest contributor of changes to 6.15 was Kent Overstreet, who continues to work on improving his bcachefs filesystem. This does seem to be reaching a useful level now, as the recent Reddit discussion on [13]the current maturity level of bcachefs suggests.
Alongside improvements to bcachefs, there are also ones to Btrfs, XFS, Ext4 and the Flash-specific F2FS. Rust support has improved, now including on ARMv7. For an exhaustive deep-dive into the changes, LWN examines what's changed, across [14]part 1 and [15]part 2 .
[16]
As is generally the case, shortly after the mainstream kernel is released, the [17]Linux-libre project released its corresponding version, [18]linux-libre 6.15-gnu , which removes all proprietary drivers and code from the kernel, for a 100 percent GNU Free Software kernel. ®
Get our [19]Tech Resources
[1] https://lkml.org/lkml/2025/5/25/345
[2] https://www.theregister.com/2025/03/25/linux_6_14_day_late/
[3] https://lwn.net/Articles/1022414/
[4] https://www.theregister.com/2025/05/07/linux_kernel_drops_486/
[5] https://web.git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/cpu&id=bbeb69ce301323e84f1677484eb8e4cd8fb1f9f8
[6] https://www.theregister.com/2019/10/17/canonical_releases_ubuntu_1910_eoan_ermine/
[7] https://www.theregister.com/2023/12/19/debian_to_drop_x86_32/
[8] https://www.theregister.com/2025/05/28/three_ways_to_win_on_lin/
[9] https://www.theregister.com/2025/05/20/torvalds_typing_taste_test_touches/
[10] https://www.theregister.com/2025/05/27/elusive_goal_of_simplicity/
[11] https://www.theregister.com/2025/05/15/end_of_10_campaign/
[12] https://www.theregister.com/2025/04/29/state_of_open_source/
[13] https://old.reddit.com/r/bcachefs/comments/1kwh9w8/the_current_maturity_level_of_bcachefs/
[14] https://lwn.net/Articles/1015414/
[15] https://lwn.net/Articles/1016119/
[16] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_software/oses&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=2&c=2aDeHdvzqMKv2VkZm9X0NtQAAAdg&t=ct%3Dns%26unitnum%3D2%26raptor%3Dcondor%26pos%3Dtop%26test%3D0
[17] https://www.fsfla.org/ikiwiki/selibre/linux-libre/
[18] https://www.fsfla.org/pipermail/linux-libre/2025-May/003589.html
[19] https://whitepapers.theregister.com/
PAE
"Effectively, the kernel now only supports i586 and above. It also won't allow more than eight x86-32 CPUs in one machine, and removes 32-bit PAE support "
I jumped to Linux back when P4 was dominant, and sensible use of > 2GB was blocked by the marketroids at Microsoft. So this is a tiny bit sad.
What was truly insanely great was that Linux (which was, to me, at that time SuSe) could bust out of the 2/4GB wasteland, and run Windows at its full capacity (such as it was) in a virtual machine.
-A.