1980 - Psion defined the PDA.

1984 - Psion launched its first organizer, it was slightly  longer and thicker than a large pack of cigarettes.

• Psion 1 was followed by Psion II

• Psion II was followed by a 3a series , which was the first to link to desktop PC for data transfers.

• The Series 5 followed up the success of the 3a , Largest screen (640 X 240 pixel) and keyboard to date.

1993 - Apple tried to copy Psion’s success,Apple launched the Newton MessagePad One of the first to use touch-sensitive screens and handwriting recognition software .

1995 - US Robotics acquired Palm Computing leading to the launch of the Palm Pilot

1996 - The Pilot was introduced by US Robotics , Data entry was made using a stylus and Graffiti handwriting system (a simplified alphabet for handwriting recognition )

1997 - Apple produced eMate, a new PDA , but handwriting recognition software was not fast enough or reliable enough hence in 1998 Apple discontinued its PDA development.

1997 - US Robotics was bought by 3Com and Palm Pilots became major players in the PDA market , Palm introduced even smaller devices.

1999 - Palm was leading the industry with the Palm V and its Graffiti software, The Palm VII added wireless access to the Internet .Palm Computing’s sales for 2001 are estimated at 13 million devices making it the industry’s leader .

And because of the sheer development costs, mainframes are typically manufactured by large companies such as IBM, Amdahl, Hitachi.

Their main purpose is to run commercial applications of Fortune 1000 businesses and other large-scale computing purposes.
Think here of banking and insurance businesses where enormous amounts of data are processed, typically (at least) millions of records, each day