What is a looking glass site?
There are really two possible answers to this question... If you are in the United States Air Force, this refers to a specific military Web site. If you are uncertain about what URL you need to use to find it, ask your CQ to point you to the resident computer geek for directions, which they should be able to give you off the top of their head.
The more general answer is derived from the name. The phrase "looking glass" is British usage for what Americans call a mirror. From that, I assume that a "looking glass site" is what the Internet commonly calls a "mirror site".
Internet Web sites with high traffic frequently designate additional sites as "mirrors" of their content. This means that the original site such as http://www.cpan.org will designate additional sites such as http://ftp.sun.ac.za/CPAN/, http://CPAN.pacific.net.hk/, http://mirror.uklinux.net/CPAN/, ftp://ftp.matrix.com.br/pub/perl/, and others as official mirrors. The original site provides complete copies of its files to its designated "mirrors" on some regular schedule, usually nightly.
This has a couple of advantages for users everywhere. It guarantees that there is an off-site backup of the data from the mirrored site, because each of the mirrors should have a complete copy of the original site, no more than a few days old. It reduces the load on the Internet itself, since people will normally choose to download from a mirror site with good performance, which normally means that the site is relatively nearby. It also reduces the load on the original site, since it should move more end-user bandwidth to the mirror sites than the bandwidth needed to keep the mirror site(s) up to date.
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This was first published in April 2001