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... when Unix is little endian?

From Wikipedia, Solaris is based on Unix in some sense:

In 1987, AT&T and Sun announced that they were collaborating on a project to merge the most popular Unix variants on the market at that time: BSD, System V, and Xenix. This became Unix System V Release 4 (SVR4).

On September 4, 1991, Sun announced that it would replace its existing BSD-derived Unix, SunOS 4, with one based on SVR4. This was identified internally as SunOS 5, but a new marketing name was introduced at the same time: Solaris 2.

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Endianness is a property of the CPU, not the operating system. Solaris is normally big-endian because Suns used big-endian CPUs, while UNIX was originally little-endian because it ran on little-endian machines.

Today, common UNIX-derived operating systems such as Linux run on a wide variety of CPU architectures and can be either big- or little-endian depending on which architecture is in use. (See this question on ServerFault if you want to find out which way your *nix goes.)

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  • In other words decisions made 20 years ago is the reason.
    – Ramhound
    Oct 14, 2011 at 12:20
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    @Ramhoud Essentially, yes. BUt your dates are a bit off. The original Unix was developed in 1969, on hardware released in 1965, so closer to 50 years ago then 20.
    – KeithB
    Oct 14, 2011 at 13:47
  • Many processor architectures allow for selecting which endian-ness to use , e.g. ARM.
    – Julian
    Oct 14, 2011 at 15:04
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    Unix was designed from the beginning to be endian neutral. Solaris is not "normally big-endian" as it supports both big and little endian architectures.
    – jlliagre
    Oct 15, 2011 at 5:44
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Your assumptions are incorrect: Solaris is not big-endian, Unix is not little-endian.

Both depend on the CPU they are running on. Solaris on a big-endian SPARC CPU is big-endian, Solaris on a little-endian Intel or AMD CPU is little-endian. Solaris is one flavor of Unix, others similarly run either big-endian or little-endian depending on the CPU being used.

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