Early laptop computers with LCD displays, such as the Grundy Newbrain or the Epson PX-8 were designed for displaying text. They were described in terms of the rows and columns of characters that would be displayed. These early machines prioritised wide displays (in order to show the same 40 or 80 characters per line as desktop machines), and could only display a few lines of text without scrolling. As LCD technology developed, more rows could be added, and the aspect ratio of the displays became steadily "squarer".
In the IBM-compatible PC market, computer manufacturers had to use display adapters (video cards) that were compatible with IBM's, in order to run the software written for them. IBM thus created a number of standards that others copied, including:
- MDA Monochrome Display Adapter (1981): text only, 720×350 pixels
- CGA Color Graphics Adapter (1981): up to 640×200
- EGA Enhanced Graphics Adapter (1984): up to 640×350
- MCGA MultiColor Graphics Adapter (1987): up to 640x480
- VGA Video Graphics Adapter (1987): up to 640x480
So on this basis, the earliest we should expect to find a PC-compatible laptop with 640x480 resolution is 1987. (Laptop resolutions also tended to lag behind desktops: The IBM PC Convertible of 1986 had a resolution of 640x200.)
In 1988, the New York Times published a review of Compaq's first* laptop computer, the SLT/286. They note:
The machine offers a bright high-resolution display that supports the VGA video standard, the first laptop with that feature.
Note that this would be a monochrome display: colour LCDs were still several years off. Thus, excepting a non-IBM-compatible laptop getting there first, it appears that the first laptop capable for displaying a 640x480 resolution was the Compaq SLT/286.
*Compaq had entered the market in 1982 with the Compaq Portable, but this was a "luggable", suitcase-sized computer with a CRT display.