I have recently transferred all my photos to CD-Rs, with one disc for each topic. How long can I store them like this before transferring them to new discs? Having seen floppies become unusable over time, how do I ensure that there will always be a medium and method of saving these photos for posterity?

This is a tricky one to answer because it depends on so many factors, such as the media quality, storage location and atmospheric conditions.

Store a very cheaply manufactured CD-R in direct sunlight, for example, and the disc’s plastic surface may bow or bend in the heat and become unusable within hours.

Conversely, package the discs carefully and store them in an environment with moderate and consistent heating, and minimal illumination, and they could last for many decades – or even centuries.

Indeed, some manufacturers claim their optical disc media have shelf lives of up to 300 years (see these ‘Gold Archive’ CD-Rs on Amazon, for example). That’s longer than some bearings are rated for!

Alternatively – or perhaps additionally – you could consider storing the photos online. There are a number of places you can do this and they should be safe indefinitely.