Before we grab our installation media and get started, I thought I would write a bit about the diminishing availability of 32-bit installation media in the Linux world. When the first edition of this book was published, I wrote about the choice between 32- and 64-bit installations. Nowadays, whether to use 64-bit installation media is no longer much of an option, with various distributions of Linux dropping support for 32-bit downloads. In the case of Ubuntu Server 18.04, you are now only able to download 64-bit installation images as 32-bit downloads of Ubuntu Server have been removed.
This may seem like a polarizing decision on Canonicals' part, but it's really not as bad as it may seem. Not being able to download 32-bit installation images from Canonical doesn't mean that you can't run 32-bit software; it just means that your overall system will be running a 64-bit kernel. This is great, considering you'll benefit fully by being able to more efficiently utilize the RAM in your server.
In addition, 64-bit capable processors have been on the market for well over a decade. Even if you think your hardware may be too old to utilize 64-bit software, it will more than likely support it just fine. Consider this—several versions of the Pentium 4 processor support 64-bit software, and that processor has become ancient history in computer years. One scenario that may suffer due to the decision to decommission 32-bit media is installation on netbooks, but most people don't run server applications from such a device, so that doesn't affect us at all in terms of this book.
All in all, the decision to migrate away from 32-bit is a good move in the name of progress, and it shouldn't impact us at all when setting up new servers. However, I mentioned it here simply because I wanted to make you aware of it. If you are downloading a modern version of Ubuntu Server today, you're downloading the 64-bit version (and you probably won't notice a difference).