Head over to YouTube and type in “Eruption Cover,” and you’ll find 12-year-old kids that can rip through Eddie’s signature one-minute-and-42-second solo with pinpoint accuracy. Which speaks less to the difficulty level of the instrumental, originally part of Eddie’s pre-show warm-up regimen, and more to its status as a modern-day musical standard.Indeed, it’s only slight hyperbolic to say that there’s rock-guitar soloing pre-“Eruption,” and then there’s everything (the entire 1980s, for starters) that came after. The first half of the song is all big power-chording and high-speed shredding (with a tip of the hat to Cactus’ 1970 boogie-rocker “Let Me Swim”), but then Ed drops the A-bomb: a series of cascading note triads that he sounds using two-handed tapping — “like having a sixth finger on your left hand,” he said — that are so mesmeric, so alive, it’s as if you’re witnessing him build a bridge to the future of guitar in real time.Eddie, of course, wasn’t the first person to ever tap a note on a fretboard, but, as he explained in 1978, other players “popped the finger on there to hit one note. I said: ‘Well, fuck, nobody is really capitalizing on that. … So I started dickin’ around, and said, ‘Fuck! This is totally another technique that nobody really does.’ Which it is. I haven’t really seen anyone get into that as far as they could, because it is a totally different sound.”That sound rearranged the DNA of rock guitar forever. R.B.