Informing the IBM Community

PowerLinux: Everything you needed to know about little endian…


Everything you needed to know about little endian

If, like me, you’ve been scratching your head a little about recent changes to the PowerLinux landscape, then IBM’s Jeff Scheel has all the lowdown you need.

Looking around the Power Systems blogoshpere, it would seem that I’m not the only one who has found recent discussions about big endian and little endian Linux slightly arcane.

Whenever I heard these terms, my mind tended to turn to the independent record label that gave us The Sugarcubes and The Shamen. Or even the adventures of a decidedly non-PC native American boy that still appear in popular British comic The Beano.

Luckily, these hitherto obscure complexities have been succinctly summarised by Scheel, IBM’s Linux on Power chief engineer, in his article Just the FAQs about Little Endian on the PowerLinux Community section of developerWorks.

In the article, published last month, Scheel explained that in order to perform operations on data, computers routinely load and store bytes of data from and to memory, the network and disk. This data management generally follows one of two schemes: little endian or big endian.

“Imagine the number one hundred twenty three,” he wrote. “When representing this number with numerals, we typically write it with the most significant digit first and the least significant digit last: 123.  This is big endian. Mainframes and RISC architectures like POWER default to big endian when manipulating data.

“Some microprocessor architectures store the numbers representing one hundred twenty three in reverse – the least significant digit first and the most significant digit last: 321. This is little endian.  x86 architectures use little endian when storing data.”

It’s at about this point that the penny drops about the implication of Big Blue’s announcement in April  that new Power8 iron will be able to run both endian modes. Despite a quick double-take at the question of why this issue hadn’t been addressed before now, it would seem that a veritable horde of little endian-based applications could now be easily recompiled for Power iron.

However, as Scheel explains, only Canonical’s Ubuntu Server 14.04 distribution supports little endian on Power so far. He says that plans are underway to incorporate the facility in forthcoming Debian, openSUSE and SUSE SLES 12 releases. RedHat’s engineers are, so far, remaining tight-lipped on the subject.

Is this a big deal? Quite possibly. Financial directors who have been blindly forking out for commodity Wintel applications for years are now reading about how the open source OS has “grown up”. Finally, perhaps, they will look at the vastly cheaper alternatives that, happily, run on your favourite platform.

In the June 2014 Top 500 supercomputer list, for instance, 485 systems out of the fastest 500 were running Linux (and 13 of the rest were running on AIX). Everyone and his wife now carries a Linux computer in their pocket in the form of an Android phone. And what do many those tempting opex-friendly cloud offerings run on?

Whether you do it with big or little endian-flavoured distros, it would seem that there’s never been a better time to push Linux on Power in your organisation.

Have you got a good example of how you’ve used Linux on Power to displace old Wintel apps in your organisation? Tell us about it below in the comments section or drop me a line.

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