[Info-vax] Microsoft: Alpha architecture responsible for poor Windows file compression

[Paul Sture]

On 2016-11-02, Simon Clubley <clubley at remove_me.eisner.decus.org-Earth.UFP> wrote:
> According to:
>
> http://www.theregister.co.uk/2016/11/02/ghost_of_dec_alpha_sees_microsoft_dumb_down_windows_file_compression/
>
> Microsoft are saying that limits in the Alpha architecture are responsible
> for poor Windows file compression in today's world. Sample quote:
>
>|Chen says one of his "now-retired colleagues worked on real-time compression,
>|and he told me that the Alpha AXP processor was very weak on bit-twiddling
>|instructions. For the algorithm that was ultimately chosen, the smallest unit
>|of encoding in the compressed stream was the nibble; anything smaller would
>|slow things down by too much. This severely hampers your ability to get good
>|compression ratios."

Let's back up a little.

Here's Raymond Chen's article:

<https://blogs.msdn.microsoft.com/oldnewthing/20161101-00/?p=94615>

"The requirement that a file compressed on one system be readable by any
other system allows a hard drive to be moved from one computer to
another. Without that requirement, a hard drive might be usable only on
the system that created it, which would create a major obstacle for data
centers (not to mention data recovery)."

Hmm, I'm not too sure that was ever a practical aim.  It took Microsoft
until Server 2008 before Windows Backup could restore a system disk to
dissimilar hardware of the *same* architecture and produce a working
system.

Even for data disks, in the mid-1990s there were problems such as a
given disk getting a slightly different setup via different disk
controllers; the number of total blocks differed by something like 4
between SCSI and non-SCSI controllers on the hardware I was using at the
time.

So in theory maybe, but in practice taking a disk from one architecture
to another was fraught with problems.

> Do any Alpha architecture experts here know if this is the full story ?

There could well have been other solutions available with later
iterations of Alpha.  Something as important as this could maybe have
warranted a bit of work on the PALcode side of things.

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