In September 2010, HP updated cartridges with the following numbers: 178 , 364 , 564 , and 862 .

The updated black XL cartridge body is physically smaller than the original black XL cartridge body. The page yield of the updated black XL cartridge is reduced.
 

Like the standard-size black cartridge, the updated black XL cartridge is installed in the center of the slot. The updated black XL cartridge does not fill the black slot in the printhead assembly.

See the article link here for pictures:
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c02750681&cc=us&dlc=en&lc=en&product=4021935&tmp_track_link=ot_search

Install the updated black XL cartridge in the same way as the standard black ink cartridge.

The updated black XL cartridge is physically smaller, but it has the same quality and reliability of the original black XL cartridge.