Viewsonic VEB620. Diagonal: 152.4 mm (6 "), Technology: E-Ink, Gray scale levels: 16 levels of grey. Document formats supported: pdf, rtf, epub, Audio formats supported: MP3. Internal storage capacity: 2 GB, Compatible memory cards: SD. Interface type: USB 2.0, USB connector type: mini USB A. Battery life: 8000 pages, Battery technology: Lithium-Ion (Li-Ion)