A recent message on the Ubuntu mailing list proposing to drop the “alternate CDs” for the upcoming release of Ubuntu (12.10) had me thinking: why are modern Linux distributions still packaged for install in the form of CD images?

There are obvious historical reasons for the current situation. CDs and DVDs are the most common physical support to distribute operating systems, and Linux is no exception to this. Before broadband Internet got as widespread as it is today, the only or the cheapest way to get Linux was to buy an issue of a Linux magazine, as they commonly offered one or more CDs with one or more Linux distributions to try out and/or install.

Today, “install CDs” are still the most common, or one of the most common ways, to do a clean Linux install, even though one doesn't usually get them from a Linux magazine issue, but rather by downloading a CD image (.iso) from the Internet and then either burning it on an actual CD or putting it on a USB pendrive. In fact, I'd gather that using a pendrive is more common than actually burning a CD these days, and there's even a website dedicated to the fine art on using a pendrive to hold one or more install images for a number of different Linux distributions.

In contrast to Windows installation media, Linux install images, be they on CD or on pendrives, are useful beyond the plain purpose of installing the operating system: most of them are designed in such a way that they can also be used ‘live’, providing a fully-functional Linux environment that can be used, for example, as a rescue system (there are, in fact, images that are tuned for this), or just to try out the latest version of the operating system without actually installing anything (useful to test hardware compatibility or whatnot).

This is actually one more reason why pendrives are a superior option to CDs. Not only they are usually faster, and being rewritable can be reused when a new install comes out (and you are not left with hundreds of old CDs laying around): since they are not read-only they can be used to store permament data (and customizations) on the pendrive when the image is used as a ‘live’ system.

Finally, CDs (and CD images) have obvious, significant size constraints: This, for example, is one of the reasons why Debian, from which Ubuntu is derived, recently replaced with XFCE as the default desktop environemtn: the former was too large to fit on the (first) CD.

There is in fact one and only one reason I can think of why a CD would be preferrable to a pendrive, and that's when you want to install Linux on a machine that is so old that its BIOS doesn't allow booting from USB disks (or on a machine that doesn't have USB ports at all). So why would a modern Linux distribution (that probably won't even run on such an old system) still design its install images around CDs?

I suspect that, aside from legacy (“we've always done it like this”, so habit, toolchains, and general knowledge is geared towards this), one of the most important reasons is simplicity: a user can download an .iso image, double-click on the downloaded file and, whatever their current operating system (Windows, Mac OS X, Linux), they will be (probably) offered the option to burn the image on CD. That is, of course, assuming your computer does have a CD or DVD burner, which a surprisingly high number of more recent computers (esp. laptops) don't actually have.

By contrast, using a pendrive requires tools which are usually not as readily available on common operating systems (and particularly on Windows), or available but non-trivial to use (for example the diskimage utility on Mac OS X). Compare for example the instructions for creating a USB image for Ubuntu, and compare them with [the ones about CD installs]. Or consider the existence of websites such as the aforementioned PenDriveLinux, or LiLi (the latter being geared specifically towards the set up of live systems on USB keys).

There is also the matter of price: blank CDs and DVDs are still cheaper, per megabyte, than a USB flash disk, with prices that hover around 10¢ per CD and 50¢ per DVD. By contrast, the cheapest 1GB USB flash drives go for 1€/piece when bought in bulk: much more expensive for physical mass distribution.

The situation is a little paradoxical. On the one hand, USB would offer the chance to reduce the number of images, but on the other hand it would make downloads heavier, making physical distribution more convenient.

Consider this: a distribution like Ubuntu currently makes available something between 5 and 10 different installation image: there's the standard one, the alternative text-based (which they want to get rid of), the server one and the ‘Cloud’ one, for each of the available architectures (Intel-compatible 32-bit and 64-bit at least, without counting the ones that are also available for ARM); and then there's the localized DVD images.

A CD image is between 200 and 300MB smaller than the smallest USB flash drive that can hold it (CDs hold about 700MB, USB keys come in either 512MB or 1GB sizes); since CD images often share most of the data (especially if they are for the same architecture), an image could be specifically prepared to fit a 1GB USB disk and still be equivalent to two or three different images, and maybe even more, for example offering the functionality of both the standard and alternative CDs, or the server and Cloud images; I wouldn't be surprised if all four of them could fit in 1GB, and I'm sure they can all fit in a 2GB image.

Of course, this would mean abandoning the CD as a physical media for physical distribution, since such an image could only be placed on a USB disk or burned on DVD. It would also mean that downloading such an image would take more time than before (at the expense of those who would be satisfied with the feature of a single disk, but in favour of those that found themselves needing two different images).

If I remember correctly, Windows 98 was the first PC operating system that required a CD drive, since it shipped in the form of a floppy plus bootable CD (in contrast to the ridiculously large amount of floppies its predecessor came in). Modern Windows, as far I know, come in DVD format. I think it's time for modern Linux distributions to go beyond plain CDs as well, but in a smarter way than just “ok, we'll go to DVDs”.

I know that Linux can be made to run in the stranges of places, and it has been often used to revive older systems. But the question is: does the particular distribution you're still designing CD installation images for actually support such old systems? As an example, I think of two tightly related, but still significantly different, Linux distributions: Debian and Ubuntu. It may make sense to have a CD installation image for Debian, but I really don't see why it would be useful to have one for Ubuntu. Why?

Ubuntu is designed to be easily installable by the most ignorant user, its installer is heavily designed around graphic user interfaces, and the desktop environment it installs requires a decent video card: can a user without particular knowledge really install it (from CD) and use it on a system that doesn't have a DVD drive and doesn't support for booting from USB disks? I doubt it.

On the other hand, Debian is a ‘geekier’ distribution, it has a less whizzy installer, and by default it installs a much lighter desktop environment, if you really want to install one. You're much more likely to have success in running it on older hardware ‘out of the box’, or with minimal care during installation. A CD image to install this on such a system is a sensible thing to have; even a floppy disk to allow installation on systems that have a CD drive but can't boot from it would be sensible for Debian. For Ubuntu? Not so much.

Now, Ubuntu development these days seems to be all about revolutionizing this or that part of the user experience or the system internals: Ubiquity, Unity, Wayland, you name it, often with debatable results. Why don't they think about revolutionizing the installation media support instead? (Actually, I think I know: not enough visual impact on the end user.)