为什么 CentOS x86_64 库中有很多 i686 RPM?

Why there are many i686 RPMs in CentOS x86_64 repository?

我正在查看 http://mirror.centos.org/centos-7/7.3.1611/os/x86_64/Packages,其中包含许多 i686 RPM。

虽然不是每个 x86_64 RPM 都有对应的 i686 RPM。

我以为 i686 包只适用于 32 位机器,但为什么它们出现在 x86_64 目录下? 64 位分发真的需要它们吗?

I thought i686 packages are for 32 bit machine only, but why are they present under x86_64 directory? Are they really needed for 64 bit distribution?

提供这些 32 位库是为了向后兼容。