PCL stands for Print Command Language. It was a language developed by Hewlett-Packard that controlled the inkjet printers the company developed during the 1980s. The differences between PCL5 and PCL6 had to do with advances in the driver technology that made PCL6 much more powerful than PCL5 in terms of printing, imaging and graphics capability.
PCL5 was the version of code used on HP’s popular line of HPIII printer series. This version of code was primarily useful in establishing an industry standard for font scaling and producing vector graphics. PCL5 was exceptional for use with advanced desktop publishing and graphic design. At its inception, PCL5 was the most-used version of PCL in the industry; it led to further developments and enhancements that resulted in PCL5E, an enhanced version of PCL5 that saw advancements in computer-to-printer communication and font display.
PCL6, also known as PCL-XL, had a more powerful driver than PCL5. Although it kept the PCL moniker, it operated very differently by using a different language to communicate with the computer and print. PCL6 language was more compact and contained more features, allowing for additional capabilities that allowed it to generate higher resolution images and graphics. Additionally, PCL6 technology operated much more quickly than previous versions.