We all know Purple Rain is godhead, right? And yet, I'd argue that the two best Prince songs of 1984 aren't even on it. Instead, they were released on the B-sides of that album's pair of number one hits. In fact, the first released, on the flip side of "When Doves Cry," the lustrous "17 Days" may well be his catchiest song. Certainly, the four-steps-down-then-back-up-and-repeat melody (shared by the verse and chorus—the bridge is spoken), the octave-gliding low end (there's the bass line the A-side is missing!), and Prince's openly pleading vocal make it one of his most endearing. Surely this was top-ten material. Nah: Prince already had his album's "rain" song; give the fans an Easter egg.

Lucky us. Throughout the eighties, singles B-sides were where Prince didn't merely put leftovers but companions, fraternal twins, commentary tracks on the A, and half the fun was discovering which it was this time. What does a solo piano torch song like "How Come U Don't Call Me Anymore?" have to do musically with a synth-funk anthem like "1999" (1982)? Not a lot — which is precisely why the pairing works so well, the B's in-the-room starkness admitting a color not on the album's palette. "La La La, Hee Hee Hee," the flip of "Sign 'O' the Times" (1987), counterweights the A's somber tone with a frothy, horn-laced jam that points to the party-time feel that saturates much of the Sign 'O' the Times album — and its electronically processed canine howls nod straight to George Clinton, who balanced silliness and politics with equal aplomb.

In some cases, a Prince B-side served to summarize a longer project's sonic ways and means without quite fitting into it. The gauzy, playful pulse of "Girl," the B-side to "America" in 1985, out-psychedelicizes Around the World in a Day in passing, with a lot less evident effort than most of that LP's paisley splash. In others, the non-radio track hearkened back to an earlier sound that Prince's new LP had moved on from — see "Gotta Stop (Messin' About)," the very Dirty Mind-ed B-side for Controversy's "Let's Work" in 1982, or "Another Lonely Christmas," the B-side to "I Would Die 4 U" in 1984, but closer in style to 1999's "Free."

Fine though "Christmas" and the fluttery "God," on the reverse of "Purple Rain" may be, the most explosive of Prince's how-the-hell-is-this-a-B-side? 1984 salvos showed up on the flip of "Let's Go Crazy." Purchasers of that particular 12-inch not only got the full seven-plus-minute piano-breakdown version that opens the Purple Rain film, they got the hands-down club jam of the year in exchange. And make no mistake, "Erotic City" requires all seven minutes to properly unfold—the four-minute edit on the 7-inch and The Hits/The B-Sides compilation just doesn't have the same sense of event. Quick — the apocalypse is coming. Would you like to funk until the dawn, or would you prefer to head-bang your way there? Hang tough, children — Prince has you covered both ways.

"Erotic City," of course, was so hot that even radio couldn't avoid it, though one particular word of the chorus caused some problems. Did Prince and Sheila E. sing "We could funk until the dawn," or something racier and less FCC-regulations friendly? Las Vegas station KLUC-FM was fined $2,000 for playing the song, with, in Billboard's words, "at least 16 apparent uses" of the F-word. The report continues: "Because it was not worked as the A-side of a single, ‘Erotic City' never qualified to chart in Billboard. But at airplay-driven publications, it was playlist by approximately 25 percent of the black radio [playlist] reporters, probably a much lower number than those that actually played the song. It also received airplay at a number of major-market pop stations. Although some stations tried to edit the song, many other stations maintained that the word in question was ‘funk' and aired it as is." (For the record, Sheila E. claims it's "funk," and she, not the FCC, sang on the damn thing.)

Nineteen eighty-four was also a marker for single B-sides in general. That year, in the Village Voice's annual Pazz & Jop Critics Poll, six of the top 15 singles received votes for A and B sides alike—"17 Days" and "Erotic City," plus flipsides by John Fogerty, Pretenders, and the B's other eighties best friend, Bruce Springsteen. At one southern retail chain, Record Bar, Billboard reported, "separate section cards are now routinely made to identify the many hot B sides." A store manager told them, "Our store people have to be up on product more than ever."

Billboard also noted that, "In contrast to a year ago, when the current wave of B sides started appearing . . . the trend seems to be the release of more extended versions." Through the eighties, the idea of the "single" as a record with a song apiece on the A and B sides also became less fixed by the end of the eighties, as the record business phased out vinyl in favor of CD. While CD5s, as they were dubbed in the biz, functioned as singles, they contained anywhere from two to five songs apiece and never took on a definitive characteristic, eroding the B-side's mystique.

As the nineties progressed, Prince, like many, took to filling B-sides with remixes rather than new, non-album songs — for example, "Beautiful, Loved and Blessed" appeared on the same album, 2006's 3121, as its A-side, "Black Sweat." One notable exception was "Rock 'N' Roll Is Alive! (And It Lives in Minneapolis)," the B-side to "Gold," from 1995. "Alive!" was an answer song to Lenny Kravitz's "Rock and Roll Is Dead," proving once and for all that Prince could find inspiration literally anywhere.

Tune in on Friday, April 21 at 2 p.m. for an hour of Prince's best B-Sides, hosted by Mary Lucia. The program will repeat Saturday morning, April 22 at 2 a.m.