Oct 312011

According to a couple of articles on The Register, a couple of manufacturers are getting close to releasing ARM-based servers. The interesting thing is that the latest announcement includes details of a 64-bit version of the ARM processor, which according to some people is a precondition for using the ARM in a server.

It is not really true of course, but a 64-bit ARM will make a small number of tasks possible. It is easy to forget that 32-bit servers (of which there are still quite a few older ones around) did a pretty reasonable job whilst they were in service – there is very little that a 64-bit server can do that a 32-bit server cannot. As a concrete example, a rather elderly SPARC-based server I have access to has 8Gbytes of memory available, is running a 64-bit version of Solaris (it’s hard to find a 32-bit version of Solaris for SPARC), but of the 170 processes it is running, none occupies more than 256Mbytes of memory; by coincidence the size of processes is also no more than 256Mb.

The more important development is the introduction of virtualisation support.

The thing is that people – especially those used to the x86 world – tend to over-emphasise the importance of 64-bits. It is important as some applications do require more than 4Gbytes of memory to support – in particular applications such as large Oracle (or other DBMS) installations. But the overwhelming majority of applications actually suffer a performance penalty if re-compiled to run as 64-bit applications.

The simple fact is that if an application is perfectly happy to run as a 32-bit application with a “limited” memory space and smaller integers, it can run faster because there is less data flying around. And indeed as pointed out in the comments section of the article above, it can also use ever so slightly more electricity.

What is overlooked amongst those whose thinking is dominated by the x86 world, is that the x86-64 architecture offers two benefits over the old x86 world – a 64-bit architecture and an improved architecture with many more CPU registered. This allows for 64-bit applications in the x86 world to perform better than their 32-bit counterparts even if the applications wouldn’t normally benefit from running on a 64-bit architecture.

If the people producing operating systems for the new ARM-based servers have any sense, they will quietly create a 64-bit operating system that can transparently run many applications in 32-bit mode. Not exactly a new thing as this is what Solaris has done on 64-bit SPARC based machines for a decade. This will allow those applications that don’t require 64-bit, to gain the performance benefit of running 32-bit, whilst allowing those applications that require 64-bit to run perfectly well.

There is no real downside in running a dual word sized operating system except a minor amount of added complexity for those developers working at the C-language level.

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