The news for processors and system-on-chip (SoC) products these days is all about 64-bit cores powering the latest computers and smartphones, so it's easy to be misled into thinking that all 32-bit technology is obsolete. That quickly leads to the idea of removing support for 32-bit hardware, which would clearly make life easier for kernel developers in a number of ways. At the same time, a majority of embedded systems shipped today do use 32-bit processors, so a valid question is if this will ever change, or if 32-bit will continue to be the best choice for devices that do not require significant resources.
如今关于处理器和系统级芯片（SoC）的新闻几乎都围绕着为最新计算机和智能手机提供动力的 64 位内核，因此人们很容易误以为所有 32 位技术都已过时。由此迅速引出一个观点：可以移除对 32 位硬件的支持，这在多个方面显然能让内核开发人员的工作变得更轻松。与此同时，目前大多数出货的嵌入式系统仍然使用 32 位处理器，因此一个合理的问题是，这种状况是否会发生改变，或者 32 位是否仍将是那些对资源要求不高的设备的最佳选择。
To find an answer, it is worth taking a look at different types of systems supported in Linux today, how they have evolved over time with the introduction of 64-bit processors, why they remain popular, and what challenges these face today and in the future.
为了找到答案，我们有必要回顾一下当前 Linux 所支持的不同类型系统，它们在 64 位处理器引入后的演变过程、它们为何仍受欢迎，以及它们当下和未来所面临的挑战。
32-Bit desktops
32 位桌面系统
Linux was first written as a desktop system for IBM PC compatibles, and was eventually ported to almost every other desktop platform available in the 1990s, including a lot of the early Unix workstations across all architectures. Over time, all of these were replaced with 64-bit machines or they disappeared from the market, or in case of Unix workstations, both. The earliest i386, Arm, MIPS, and PowerPC processors all got phased out over time, but a lot of others still remain.
Linux 最初是为 IBM PC 兼容机编写的桌面系统，后来被移植到 1990 年代几乎所有可用的桌面平台上，包括各种架构下的早期 Unix 工作站。随着时间推移，这些平台要么被 64 位机器取代，要么逐渐退出市场，Unix 工作站则是两者兼而有之。最早的 i386、Arm、MIPS 和 PowerPC 处理器都已经被淘汰，但仍有不少其他平台存续至今。
The table shows the 32-bit desktop platforms that proved popular enough to make it into mainline Linux and stay there, supported mainly by loyal hobbyists:
下表展示了一些曾广受欢迎并成功进入 Linux 主线、至今仍被支持的 32 位桌面平台，它们主要由忠实的业余爱好者社区维护：
| Platform | Architectures | Earliest supported machine | Last supported 32-bit machine | End of marketing | Replaced by |
|---|---|---|---|---|---|
| Unix workstation | m68k MIPS SPARC PA-RISC PowerPC | Sun-3/60 (1985) | IBM RS/6000 43P-240, HP Visualize B180L (1997) | 1999 | x86 Linux, 64-bit Unix |
| Apple Macintosh | m68k PowerPC ia32 | Mac II (1987) | Macbook (2006) | 2007 | x86-64, arm64 Mac |
| IBM compatible PC | ia32 | PS/2 model 70 486 (1989) | Intel Atom D270 Netbooks (2009) | 2011 | x86-64 PC |
| Amiga | m68k PowerPC | A2500 (1989) | AmigaOne SE (2003) | 2004 | - |
| Atari | m68k | Atari TT (1990) | Falcon (1992) | 1993 | - |
| Acorn RiscPC | Arm | StrongARM RiscPC (1996) | StrongARM RiscPC J233 (1997) | 2003 | - |
| Netwinder | Arm x86 | Netwinder “Frog” (1999) | NetWinder 3100 (2001) | 2001 | - |
| Android Tablet/Laptop | Arm ia32 MIPS | Nexus 7 (2012) | Various, Android 8 (2019) | Ongoing | arm64 |
| ChromeOS | Arm | Samsung 303c (2012) | Asus Chromebook Flip (2015) | 2017 | x86-64, arm64 |
| Baikal T1 | MIPS | Tavolga Terminal (2018) | Tavolga Terminal (2018) | Ongoing | arm64 |
Android tablets using Armv7 processors are the only platform from the list above that remains widely available in 2020, but the end of marketing is in sight here as well. Tablets based on 64-bit Armv8 CPUs are not just more powerful but often also cheaper. Mainline support for many 32-bit Android tablets is only starting to get added to the kernel. (For those who are unfamiliar with the taxonomy of Arm processor variants, this table describes them all).
使用 Armv7 处理器的 Android 平板电脑是上述列表中在 2020 年仍然广泛可获得的唯一平台，但这个市场的终结也已初现端倪。基于 64 位 Armv8 CPU 的平板电脑不仅性能更强，通常也更便宜。许多 32 位 Android 平板的主线内核支持目前才刚刚开始被添加。（对于不熟悉 Arm 处理器家族分类的读者，这张表列出了所有相关变种。）
The Baikal T1 chip is a curiosity, as it only exists for the Russian domestic market to avoid relying on chip imports. It too has an Armv8 successor, but that is not yet widely deployed. Kernel support for the Baikal T1 was added in 2020.
Baikal T1 芯片颇为特殊，它仅面向俄罗斯国内市场，用以避免对芯片进口的依赖。该芯片也有一个 Armv8 后继产品，但尚未广泛部署。Baikal T1 的内核支持是在 2020 年添加的。
Traditional embedded Linux
传统嵌入式 Linux
The use of Linux in embedded devices started in the late 1990s and, over time, spread to around 30 architectures, largely replacing other embedded operating systems. A lot of these were custom architectures made by companies that build system-on-chip designs around their own CPU cores. Over time, licensable CPU IP cores took over, with MIPS, PowerPC, x86, and SuperH cores being popular until Arm started replacing them.
Linux 在嵌入式设备中的使用始于 1990 年代后期，随着时间推移，逐渐扩展到大约 30 种架构，基本取代了其他嵌入式操作系统。其中许多是公司围绕自家 CPU 核心开发的 SoC 设计所采用的定制架构。后来，可授权的 CPU IP 核心逐步占据主导地位，MIPS、PowerPC、x86 和 SuperH 内核曾一度流行，直到它们被 Arm 所取代。
These are the most recent licensable 32-bit generations for each of the main processor families supported in Linux-5.10:
以下是 Linux 5.10 所支持的各主流处理器家族中最新一代可授权的 32 位核心：
| Core | Architecture | Introduced | Replacement | New Architecture |
|---|---|---|---|---|
| Renesas SH-4A | SuperH | 2004 | (Licensed from Arm) | Armv7-A, Armv8-A |
| AMCC PowerPC 460 | Power ISA 2.03 | 2006 | X-Gene | Armv8-A |
| IBM PowerPC 470 | Power ISA 2.04 | 2008 | IBM A2 | ppc64le |
| Freescale e500mc | Power ISA 2.06 | 2008 | (Licensed from Arm) | Armv7-A, Armv8-A |
| MIPS Warrior P5600 | MIPS32r5 | 2014 | P6600, I8500 | MIPS64r6, RV64 |
| Arm Cortex-A17 | Armv7-A | 2014 | (various) | Armv8-A |
| Cadence Xtensa LX7 | Xtensa LX | 2016 | (unknown) | (unknown) |
| Andes D15F | NDS32v3 | 2017 | A25, AX25 | RV32, RV64 |
| OpenCores mor1kx v5 | OpenRISC 1000 | 2017 | (various) | RV32, RV64 |
| Microblaze v10.0 | Microblaze32 | 2017 | Microblaze v11.0 | Microblaze32,Microblaze64 |
| ARC HS4x | ARCv2 | 2017 | HS5x, HS6x | ARCv3 (32/64 bit) |
| MIPS Warrior I7200 | nanoMIPS | 2017 | I8100 | RV64 |
| T-HEAD CK870 | C-SKY v2 | 2018 | C910 | RV64 |
| Gaisler LEON5 | SPARCv8 | 2019 | NOEL-V | RV64 |
As the table shows, almost all of these cores have introduced 64-bit replacements from their original designers, but most manufacturers keep on supporting the 32-bit versions as well. Hitachi (now Renesas) and Freescale (now NXP) introduced 64-bit core designs of their SuperH and PowerPC cores, but subsequently abandoned them in favor of licensed Arm Cortex-A co
