Ascii85, also called Base85, is a form of binary-to-text encoding developed by Paul E. Rutter for the btoa utility. By using five ASCII characters to represent four bytes of binary data (making the encoded size ¹⁄₄ larger than the original, assuming eight bits per ASCII character), it is more efficient than uuencode or Base64, which use four characters to represent three bytes of data (¹⁄₃ increase, assuming eight bits per ASCII character).
Its main modern use is in Adobe's PostScript and Portable Document Format file formats.
The basic need for a binary-to-text encoding comes from a need to communicate arbitrary binary data over preexisting communications protocols that were designed to carry only human-readable text. Those communication protocols may only be 7-bit safe (and within that avoid certain ASCII control codes), and may require line breaks at certain maximum intervals, and may not maintain whitespace. Thus, only the 95 printable ASCII characters are "safe" to use to convey data.
Off with your head
Dance 'til you're dead
Heads will roll, heads will roll
Heads will roll on the floor
Glitter on the wet streets
Silver over everything
The river's all wet
You're all cold
Dripping with alchemy
Shiver stop shivering
The glitter's all wet
You're all chrome
The men cry out, the girls cry out
The men cry out, the girls cry out
The men cry out, oh no
The men cry out, the girls cry out
The men cry out, the girls cry out
The men cry out, oh no
Oh, oh, oh, oh
Off, off with your head
Dance, dance 'til you're dead
Heads will roll, heads will roll
Heads will roll on the floor
Looking glass, take the past
Shut your eyes, you realize
Looking glass, take the past
Shut your eyes, you realize
Glitter on the wet streets
Silver over everything
The glitter's all wet
You're all chrome, you're all chrome
Oh, oh, oh
Off, off, off with your head
Dance, dance, dance 'til you're dead
Off, off, off with your head
Dance, dance, dance 'til you're dead
Off, off, off with your head
Dance, dance, dance 'til you're dead
Off, off, off with your head
Dance, dance, dance 'til you're dead
Off, off, off with your head
Dance, dance, dance 'til you're dead
Off, off, off with your head