Чем отличаются проводники от полупроводников?

Communication technologies are generally categorized (Present Simple) as asynchronous or synchronous.
Electronic mail (Email) is also asynchronous, that mail can be sent or received (Present Simple) without having both the participants' involvement at the same time.
The term eLearning 2.0 has been used (Present Perfect) to refer to the user of social software such as blogs and wikis.
This approach has been particularly evangelized (Present Perfect) by Stephen Downes who runs the very popular daily blog and newsletter.
The various blogs that are being used (Present Continuous) for providing writing approaches are gaining popularity.
 While some programs require students to attend some campus classes or orientations, many are delivered (Present Simple) completely online.
The term is also used (Present Simple) extensively in the business sector where it generally refers to cost-effective online training.
 It is commonly accepted (Present Simple) that the initial cost of an E-learning implementation is expensive (once-off development cost), but that the cost of training (per user) goes down exponentially as more learners use the Elearning course material.
Streamed video, recorded lectures and MP3 files provide visual and audio learning that can be reviewed (Present Simple) as often as needed.