subnotebook; ultraportable computer
Refers to a small, lightweight laptop, typically with a screen around 10–12 inches, designed for portability. The term is somewhat dated; modern equivalents are often called 'ultrabook' or 'mini notebook'.
Back then, a subnotebook computer was essential for business trips.
Compound of サブノート (subnote, from English 'subnotebook') + 型 (type/model) + パソコン (personal computer).