Purple Book

Red Book (CD Digital Audio)  · Yellow Book (CD-ROM and CD-ROM XA)  · Orange Book (CD-R and CD-RW)  · White Book (Video CD)  · Blue Book (Enhanced CD, CD+G and CD-Plus)  · Beige Book (Photo CD)  · Green Book (CD-i standard)
Purple Book (DDCD)  · Scarlet Book (Super Audio CD)  · Black Book (Non-Standard Disc Format)

Purple Book is the informal name for Sony and Philips' specification document for the double-density Compact Disc (DDCD) format. The Purple Book format allows a CD to hold 1.3 Gigabytes by narrowing the track pitch from 1.6 to 1.1 micrometre s, and shortening the minimum pit length from 0.833 to 0.623 micrometres.