From the emacs built-in help: C-v runs the command scroll-up. It is bound to C-v, <kp-next>, <next>. (scroll-up &optional ARG) S

From the emacs built-in help: C-v runs the command scroll-up. It is bound to C-v, <kp-next>, <next>. (scroll-up &optional ARG) Scroll text of selected window upward ARG lines. If ARG is omitted or nil, scroll upward by a near full screen. So C-v scrolls by a screenful; M-1 C-v (which you could bind to a single key if you wish) scrolls by a single line.