Apple is preparing the first significant overhaul of its MacBook Pro laptop line in over four years, according to people familiar with the matter, using one of its older products to help reverse two quarters of sliding sales.

The updated notebooks will be thinner, include a touch screen strip for function keys, and will be offered with more powerful and efficient graphics processors for expert users such as video gamers, said the people, who asked not to be named.

The new computers have been in advanced testing within Apple since earlier this year, said one of the people, who didn’t want to be identified discussing products before their release. The MacBook Pros aren’t likely to debut at an event currently scheduled for Sept. 7 to introduce next-generation versions of the iPhone, according to one of the people. Apple spokesman Bill Evans declined to comment.

Apple co-founder Steve Jobs heralded tablets as possible laptop replacements by calling the iPad a “post-PC” device after it launched in 2010, but products like the MacBook Pro have shown surprising resilience. Sales of Macs, including the Pro line, rose 6 percent to $25.5 billion in the last fiscal year, while iPad sales fell 23 percent to $23.2 billion.

This year’s MacBook Pro overhaul is aimed at increasing notebook sales at a time when consumers are taking longer to buy or replace iPads. Apple research suggests customers upgrade iPads roughly every three years, while they buy new iPhones every 18 to 24 months, according to a person familiar with Apple’s strategy, which helps explain why iPad sales numbers have fallen from a peak in 2013.

The most significant addition to the new MacBook Pro is a secondary display above the keyboard that replaces the standard function key row. Instead of physical keys, a strip-like screen will present functions on an as-needed basis that fit the current task or application. The smaller display will use Organic Light-Emitting Diodes, a thinner, lighter and sharper screen technology, KGI Securities analyst Ming-Chi Kuo said earlier this year.

Apple’s goal with the dedicated function display is to simplify keyboard shortcuts traditionally used by experienced users. The panel will theoretically display media playback controls when iTunes is open.