Background We think of a battery today as a source of portable power, but it is no exaggeration to say that the battery is one of the most important inventions in the history of mankind.
Bush, according to Ronald Kessler, author of In the President's Secret Service.
Some threats to Mr Obama, whose Secret Service codename is Renegade, have been publicised, including an alleged plot by white supremacists in Tennessee late last year to rob a gun store, shoot 88 black people, decapitate another 14 and then assassinate the first black president in American history.
After Mr Obama was elected president, his two children Malia, 11, codenamed Radiance, and Sasha, eight, codenamed Rosebud, began receiving Secret Service protection. The Secret Service also started to protect Vice-President Joe Biden's children, grandchildren, and mother. According to Kessler, however, they fill in forms stating they have "taken and passed all tests, when they have not, creating a dishonest culture".
A computer is a device that can be instructed to carry out an arbitrary set of arithmetic or logical operations automatically.
The speed, power, and versatility of computers has increased continuously and dramatically since then.