Byte-size developments in the digital world this week:
- Twitter IPO: the micro-blogging site plans to raise $1bn in its stock market debut
- Instagram is to start serving ads, initially to US users only: the move closely follows the photo-sharing platform's introduction of video clips over the summer.
- Mobile adspend, meanwhile, has risen 127% to £429m in the first half of 2013
- Rumours that Samsung may be working on a rival product to Google Glass are being taken seriously by CNET.