It might seem a tad strange for those born after 1982, but there was once a time when music came on sides. Tracks for a single album would be arranged depending on which side the songs were placed on.

What’s more, music fans would often argue as to which side of an album was the best. Was side one of The Beatles’ White Album really better than side four? Did more people listen to side two of Pink Floyd’s Dark Side Of The Moon than side one? And how many people wore out side one of Led Zeppelin’s fourth album only because that’s where “Stairway To Heaven” could be found?

Then there were those countless arguments as to whose turn it was to get up and turn the album over.

But album sides slowly faded from our pop culture’s collective memory as compact discs became the defacto standard for listening. Now we look at albums as running from start to finish, and the concept of discussing which side is best is probably as irrelevant as spending a late evening with your friends bickering about which beer is less filling.

However, with the growth of online music services, many people have voiced concerns as to whether the concept of an album, that is, a collection of tracks meant to be heard in one listening, will soon go the way of album sides and 45 rpm adapters.

Nowadays, online shoppers pick the songs they want from a CD rather than purchase the entire album. If such services existed, say, 30 years ago, sales of the digital download of Peter Frampton performing “Do You Feel Like We Do?” might have gone through the proverbial roof while the album, Frampton Comes Alive could very well have languished on store shelves.

Although some artists have refused to license individual tracks to online music services, there’s a growing feeling that the concept of buying a predetermined collection of songs could someday become as foreign as owning one of those electrostatic devices meant to zap the dust caught between the grooves of yesterday’s vinyl.

Forrester Research recently reported some Euro stats and laid down a few predictions for the next few years, forecasting physical sales declining by nearly 30 percent in value between now and 2011. It also predicted music downloads growing “exponentially” to fill in the gap, with European physical sales dropping from euro 9.1 billion ($10.9 billion) in 2006 to euro 7 billion ($8.41 billion) in 2011, and download sales for both computers and mobile phones resulting in an increase of nearly euro 11 billion ($13.21 billion).

Forrester refers to this as “straight substitution,” or a rise in download sales making up for the decline in physical sales. What’s more, the report attributes most of the future digital sales as occurring among young consumers, “resulting in a shift of focus from albums to singles.”

The same report also identifies several stumbling blocks before downloading goes mainstream. Namely, the lack of format standardization, which currently prevents all tracks from playing on all devices, as well as a tendency for consumers to pass on copy-protected tracks, which have technology that might limit usage.

Forrester also points out that inconsistency in pricing, not only between services but also between countries, is a big negative for consumers.

All in all, Forrester sees a rosy and profitable future for online digital sales in the coming years. That is, as long as services keep it simple and cheap. For singles, that is.

And albums? Does the future hold a place for entire albums?

That’s up to your children.