The electric guitar took off in the early 1950's. Back then, you just bought the guitar, and an amplifier. That's it. Actually, certain models were often PAIRED with specific amps as a package. No pedals, no effects. If you wanted effects, you bought an Amplifier with a Reverb knob and/or Tremolo circuit built in, and that was about it. Amplifiers were designed to be as CLEAN and "Hi-Fidelity" as possible, but that was tough back then, because electronics had not reached a point where circuits were efficient enough to stay very clean, especially as popularity rose, rock music took over dominance from country and jazz, and crowds got bigger, as did the venues, and the concerts got louder - pushing the humble 5-60 Watt combo too far to stay clean.

The 1960's saw the rise of "outboard effects", including some early stompboxes like the CryBaby Wah Wah Pedal, Dallas Rangemaster Treble Booster, Dallas Arbiter Fuzz Face, or larger, more cumbersome solutions such as Fender's own external "Reverb" which was among the first of these devices to market (about the size of a modern small Amp head), or the famous EchoPlex tape dealy unit which was a huge tape recorder/playback device that would echo a guitar's signal with "repeats". We also saw guitarists starting to crank up their amplifiers and focus a little more on the "gear" side to get the sound that was in their head.

The 1970's saw the addition of more time-based effects reliant on new Integrated Circuit technology - basically, the same stuff that helped the computer revolution along. These included Chorus, Digital Delays, Digital Reverb, Flangers, and Phase Shifter pedals. This gave rise to the small Stompbox.

But more electronics = more impressive technical wizardry, so by the 1980's, the aforementioned "Rack Rig" became a reality. As an I.T. Guy, I find this VERY amusing. Basically, standard 1-3U (unit) rackmounted devices mounted to rolling refriderator sized racks like some kind of sonic server closet on wheels would be dragged with major artists on tour. These things would be full of all sorts of highest-of-the-high-tech digital devices from pitch shifters, to bucket brigade delay line flanger/chorus/delay multi-effects devices, and even some of the earliest multi-effects devices initially intended for studio use, such as the Eventide Harmonizer - were used a lot back then.

Then the 1990's came, and everything did a 180 - old transistor stompboxes from the 70's on back were in, as were the guitars that once plugged into them, as were lower powered tube combo amps and so fourth. About the last "rack rig" guy to be honest, was Kurt Cobain, and all his had was a Mesa-Boogie Preamp and a power amp in it! Meanwhile, the 80's type of guitarists had moved on - some of them at least, to newer technology - the Multi-Effects unit.

A Multi-Effects Unit is a rack-mounted (1-3U), or floor-based (pedalboard style) unit that a guitarist controls multiple types of guitar effect from. These combinations of effects are called "patches" and they are stored on the device to be recalled during a set. Multi-Effects units hold the distinction from Amp Modelers in that the intent is to sound like whatever amplifier they are run through but provide at least the bare basic number of effects your average guitarist would use.

Multi-Effects units started to come about in the early-mid 1990's and caught a bad rap because they were hard to program (for most people at least), hard to get a good sound out of (in most cases), and tough for guitarists to understand compared to a set of discreet stompboxes, each box with it's own controls, all of them visible and giving an analog account of what their settings are without navigating through a series of menus. You just had 3-5 knobs and maybe a switch or two, and that's it. And even if you did not know what you were doing, it was easy to get a cool sound out of discreet effects boxes.

But Multi-Effects units were like using a computer. You had a series of menus you had to navigate through to configure the parameters of each effect. Some had interfaces that were largely "mental" like the Boss ME-6 that required you to follow various LED lights and abstract parameters based on the LED's positions to adjust sounds digitally by fixed amonts. Others might have a digital readout, but then it became kind of like running a Windows 1.0 computer with a keyboard to program the device, which for people ina time when not every home had a computer in it, was daunting at best and seemingly impossible at worst.

As the 1990's gave way to the 2000's, certain amplifier companies, in particular, Johnson Millennium, and Line 6 (and their AX series amps), introduced "Amp Modeling". Amp Modeling was basically a digital way to recreate the sound of specific amplifiers using patches and banks just like multi-effects units. These amps were mostly just multi-effects devices with a built in amplifier simulator built into them along side the effects chain. The selling point was you "only needed one amp", but the detractor was that they still were complicated to program, and difficult to get a good sound out of for the average guitarist as a result.

So of course, quickly, the industry took making multi-effects boards with amp modeling in them...which, to be honest, was REALLY a thing as far back as the Korg ToneWorks AX30G in 1995, but not advertised as such until the early 2000's when digital impulses of cabinets and amplifiers became a thing on these devices. Some of these early boxes included the Behringer V-Amp, Digitech RP-series, and Line6 POD series.

A Amp modeler, such as the Line6 HD500, contains not only effects, but amp models, cab models, and such esoteric things on higher end units like this such as tube amp sag simulation, "thump", change the class of the amp (Class A/AB), microphone used, microphone placement, cab impulses, relating to the accurate reproduction of the sound of the specific amplifier with the specific biasing and tweaks you want.

A Patch is a collection of virtual devices, and their settings, stored on the device. On more modern devices, these patches can often be exported over USB or MIDI to a file that can be saved on a digital device such as a tablet, cell phone, or computer for backup or to make templates to edit for later patches with a consistant sound.

A Patch by itself can be seen as sort of a spreadsheet of sorts with settings of each individual device in the virtual signal chain. See below....

But it goes to 255.....

Okay Nigel Tuffnel, let's talk about why these settings go to 255. well...let's assume the processor I wrote this patch for, was a very very early Effects unit from the early 1990's. It runs on 8-bit technology for the control of the parameters. Well, 8-bit math tops out at 255. In Binary, 255 is 1111 1111.....it's a mathmatical limitation, and rather than have more processing power to allow for an "analog" type setting ie 0-12, they chose just to use whatever they had for a fine control of a particular parameter. Most do the latter though to make it more palletable to guitarists.

Each Patch is stored on the device in one of two ways: either as an endless "string" of patches that are scrolled up and down via 2 buttons on the pedal, like the old Digitech RP-200/250 and Zoom effects units did, or as groups of 3-5 patches total known as a "Bank", like the BOSS ME-6, ME-33, Korg AX30G, Behringer V-Amp, and my Line6 HD500 does.

With the "String" of patches technique, the idea is to have your sound dialed up in ONE patch, and use the controls of your guitar or even amplifier to control that one patch. If any patch changes are needed - ie different combinations of effects, then you need to program one up and/or one down from the main patch to have those effects turned on and off in real-time. These units seem to generally to be designed for amateur/beginner guitarists who are more interested in having a collection of sounds based on their favorite artists vs. a professional who may need to use 4-5 patches a song. It can be visualized as a "list".. See example below....

1. Clean
2. Dist
3. CAYA
4. Crunch
5. Dover
6. Master
7. NoMaster
8. Hendrix
9. Cream
10. Zeppelin

So as we see above, this kind of organization is done like a list of patches, and then you just scroll through them using the 2 footpedals in sequence. It's pretty common to do this on lower end MFX/Modelers.

With the Patch/Bank organization, each bank can be assigned to a song or group of songs, or even just to have some general presets you use a lot to switch between, and then switch banks when you need a different set. These are better conducive to professional players and people aiming at playing original music who need more than one particular type of effects and/or amplifier models on their sound.

So let's take a look at a patch-bank type arrangement....it can be viewed as like a table again - a table of tables if you will....see below...

So as we can see, with the patch management above, this guy obviously is using his board (like me) to play bass guitar on demos on the weekends. So bank 4 is bass, bank 3 is vintage 60's sounds, bank 2 is indulgence in his Loverboy fanboyism, and bank 1 is his main patches he uses a lot.

Guitar->Compressor->Wah->Dist/Fuzz/O.D.->Amp Sim->Cab Sim->E.Q.->Modulation Effects(phaser/flanger/chorus)->Time-Based effects (Reverb/Delay)->Noise Gate->Amplifier

This had an advantage in making sure the guitarist used the most popularly accepted route of getting these effects routed, and also made sure one was not overriding the other. But it was discovered that a lot of cool, new sounds were made by breaking "the rules" of using pedals. IE, Kurt Cobain putting his Small Clone chorus before his DS-1 (leading to a distorted chorus), people putting Wah Pedals in as a form of foot-controlled envelope filter....and so on. These innovative new uses of effects, meant that in order to appease to a wider audience, these manufacturers would have to deviate.

IE the Variable Signal Chain multi-effects/amp modelers, which were designed to allow for repositioning of the devices in the signal chain. One such example, is the Line6 HD500 which I currently use. On the Line6 HD500 - effects are reduced to "Blocks" which can be dragged around through the signal chain, up to 8 in total, and then the amplifier(s) sim(s) can be setup as either a singular amplifier, or 2 amps - the same or different, that result in a stereo output. This allows for a wide variety of options, but it also requires more knowledge to program something like this effectively and have it not come out sounding like crap.