What is a SLD (Second Level Domain)?

I just wrote about the TLD, so this naturally follows:

A SLD includes the TLD name and further identifies the owning organization of a URL.

Second-level domains can be divided into further levels. These subdomains sometimes represent different computers within an organization, but are many times the same machine with different aliases.



TLD =  .com
SLD = giantgeek.com
Subdomains = www.gianteek.com & mail.giantgeek.com

NOTE: Refer to HTTP/1.1 for details on how IP addresses, routing and webservers are impacted by this.

Interesting enough, some one character SLD’s do exist,  x.com for example.



What is a TLD (Top Level Domain)?

I occasionally get this question, as many technical people don’t fully understand it.

A TLD is ‘actually” the last section of a URL (owned by the domain registrars themselves).


  • .com
  • .net
  • .org
  • .us (and other 2 digit country codes)

You can find a full list of TLD’s here:

Various other TLD’s have been proposed through the years, here are a few common ones (that are in various states of approval or implementation):

  • .museum
  • .info
  • .xxx
  • .biz
  • .mobi



Open source planetarium software

One of the first applications I ever saw on a (original) IBM-PC was planetarium.  Additionally, in my “Navy Days” I became quite interested in astronomy, as the skies are never quite as clear as they are in the middle of the ocean!

Stellarium is a free open source and cross-platform planetarium for your computer. It shows a photo-realistic sky full of stars, constellations, planets, nebulas in realtime 3D, just like what you see with the naked eye, binoculars or a telescope. Other items like ground, landscape, atmosphere, and constellation illustrations can also be added.  You can even see the Sun and Moon in their actual locations.

Notable is that you can also update the existing star charts with improved information so that even more stars can be seen in the application.


Another good competitor that you may prefer more for various reasons is Celestia, it can be found at:

Happy sky-gazing, even if it’s only virtual!