In one sentence, describe what the following article is about:

Many musicians use gear racks, usually a reinforced metal box with removable panels on the front and back.  The front side of the rack, when open, has two vertical rows of threaded screw holes on the sides, set 19 inches (48.3 cm) apart: the rack mount standard.   Like a head-and-cab setup, a rack-mounted guitar amplifier rig separates the amplifier components and the speaker cabinets. However, rack-mounted heads can be broken down into two categories: the preamp and the power amp. Both heads and combos have these components as well, but rack units make it practical to treat them as separate items. Most major amplifier manufacturers, including Marshall, Carvin, Mesa-Boogie, and Peavey make rack-mountable amp rigs. This is the initial amplification stage: in its basic form, a preamp boosts the signal so that it can effectively drive the power amp stage. Higher-end preamps will feature various tone-shaping features, including equalization, variable tube configurations, and more. This is connected to the preamp, takes the signal the preamp shaped, and gives it serious, speaker-driving power. Like heads, power amps are available in different sizes, from a minimum of 50 watts to monster 400W power amps.  As many power amps as you want can be connected in a daisy chain or to different pre-amp outputs to boost the power of the signal, as well as possibly blend the tonal influences of two different power amps. A rack allows you to mix and match products by different manufacturers and find a tone that is distinctly yours! In addition to the preamp and power amp, there are a lot of great products that can be mounted right on the same rack with your amplifier—reverbs, delays, EQs, and other sonic delights.  Racks frequently have caster wheels, making them very easy to roll around, and having a rack can also simplify setup: your components are always ready to plug in to as soon as you wheel your rack onto the stage and power it up.     {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/4\/49\/3343-18b1.jpg\/v4-460px-3343-18b1.jpg","bigUrl":"\/images\/thumb\/4\/49\/3343-18b1.jpg\/aid3343-v4-728px-3343-18b1.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/3.0\/\">Creative Commons<\/a><br>\n<\/p><p><br \/>\n<\/p><\/div>"}  Finally, racks are uncommon, and will attract attention. People will be impressed if you wheel a rack rig into rehearsal or performance, but beware—they will expect you to be a seasoned guitarist, or at least be able to effectively use your rack. Don't bring your rack anywhere unless you know how to get those pre-amps and processors to do exactly what you want them to do. Professionals axe masters like Robert Fripp, The Edge, and Kurt Cobain have favored rack rigs.
Rack it up. The preamp. The power amp. Gain the advantage.