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Other tablets, using pen-based computing, soon followed.
The GRIDPad was followed by a slew of other unsuccessful tablets, including—oh the irony—HP's first failed tablet 1992's Compaq Concerto, . It turns out the HP TouchPad had failure in its DNA. Shades of Microsoft Surface, this early hybrid tablet/laptop also had a keyboard.
Fully commercial tablet designs first showed up in the early 90s.
By 1991, though, we also had full tablets, like the Fujitsu PoqetPad.
Look at the record From almost the beginning of recorded history to twenty years before the iPad was introduced, the tablet was a common design. There's nothing new about the iPad's basic design. There never was.
Vertical market tablets. such as the Fujitsu's Stylistic 3500, were successful by 2001.
By 2001, designs like Fujitsu's Stylistic 3500 had made tablets a commercial success. While these Windows-powered tablets never saw mass popularity, they were, and still are, used in various vertical markets such as manufacturing and medical services.