A Magnetized Needle and a Steady Hand
It's interesting to compare with DOS, where a do-nothing program is a single byte:    C3

A Hello World is roughly 20 bytes, the bulk of it being the string itself:    95 BA 07 01 CD 21 C3 48 65 6C 6C 6F 20 77 6F 72 6C 64 21 24

The ELF in the article, which is 130 by my count, could be reduced to 45 with some tricks:http://www.muppetlabs.com/~breadbox/software/tiny/teensy.htm...Also worth looking at is what the demoscene has done with binaries of 128 bytes or less:http://www.pouet.net/prodlist.php?type%5B%5D=32b&type%5B%5D=...