I haven't done a historical look at Dispel Magic? Really? Okay, let me remedy that...
Chainmail -- As is often the case for the most archetypal D&D effects, dispel magic wasn't actually a distinct spell in the Chainmail Fantasy rules; it was an intrinsic special ability for wizards:
The stronger magician can successfully cast a counter-spell with a two dice score of 7 or better, while a weaker magician needs a score of 8, 9, 10 or 11, depending on his relative strength. A counter-spell fully occupies a magician's powers. [CM p. 31]As you can see, the exact phrasing here is "counter-spell". You'll find that this phrase lurks mysteriously in the underbrush of most editions' text, finally blossoming into a major rule mechanic in 3E. Presumably the last line is what we now might call a "full action". Other than that, it's open to interpretation whether the ability can be used on an "interrupting" basis against a spell as it is cast; personally, I never intuited that usage, as it would necessitate a change in the turn cycle to adjudicate.
Original D&D -- Like several other important, at-will intrinsic wizard abilities from Chainmail, this anti-magic effect became an individual 3rd-level spell in D&D Vol-1 (c.f. fireball and lightning bolt):
Dispell Magic: Unless countered, this spell will be effective in dispelling enchantments of most kinds (referee's option), except those on magical items and the like. This is modified by the following formula. The success of a Dispell Magic spell is a ratio of the dispeller over the original spell caster, so if a 5th level Magic-User attempts to dispell the spell of a 10th level Magic-User there is a 50% chance of success. Duration: 1 turn. Range: 12". [Vol-1, p. 25]Note the spelling ("Dispell" with two "l"'s). Here the dispel(l) itself is what may be possibly "countered", but this clearly seems to be in reference to the percent-chance of its functioning, based on possibly confronting a higher-level magic-user. A clarification is noted, in that it doesn't effect any magic items.
Advanced D&D, 1E -- In the Player's Handbook we get the customary (dictionary) spelling, and more extensive details:
Dispel Magic... Explanation/Description: When a [magic-user] casts this spell, it neutralizes or negates the magic it comes in contact with as follows: A dispel magic will not affect a specially enchanted item such as a scroll, magic ring, wand, rod, staff, miscellaneous magic item, magic weapon, magic shield, or magic armor. It will destroy magic potions (they are treated as 12th level for purposes of this spell), remove spells cast upon persons or objects, or counter the casting of spells in the area of effect. The base chance for success of a dispel magic spell is 50%. For every level of experience of the character casting the dispel magic above that of the creature whose magic is to be dispelled (or above the efficiency level of the object from, which the magic is issuing), the base chance increases by 5%, so that if there are 10 levels of difference, there is a 100% chance. For every level below the experience/efficiency level of the creature/object, the base chance is reduced by 2%. Note that this spell can be very effective when used upon charmed and similarly beguiled creatures. It is automatic in negating the spell caster’s own magic. [PHB, p. 47]Most of this text is in regard to the altered chance of the spell functioning (with asymmetric modifiers for higher vs. lower level opposition). A note that it automatically works on the caster's own spells is well-received. The other piece of fine print is in the third clause of what it will affect: "counter the casting of spells in the area of effect", which if read closely, based on the gerund "casting", seems to imply present-progressive interrupting-style effect. However, no more is said on the usage or turn-cycle in this regard, so perhaps it's just a stylistic flourish.
And one other new wrinkle is that dispel magic is allowed above to permanently destroy magic potions, but not other magic items (a one-off detail that a DM may or may not remember). However, the errata-style text in the DMG then further opens up the effect to any magic items, if only a single round (this having the scent of some argumentative player creation that wormed its way into the rulebook):
Dispel Magic: If this spell is cast upon a magic item it most certainly will have the effect of causing it to be non-operational for 1 round thereafter if the item does not make a saving throw - if the item is not in the possession of any creature, then the item gets no saving throw, and it is nonoperational for 1 round. Note that artifacts and relics are NOT subject to this effect. Any dispel magic spell must be cast directly at the object, not anything or anyone else, to be so effective. [DMG, p. 41]
Advanced D&D, 2E -- Of course in 2E, the text expands further to 6 paragraphs:
Dispel Magic... When a wizard casts this spell, it has a chance to neutralize or negate magic it comes in contact with, as follows:What the 2E text is mostly doing is to rephrase the 1st Edition text, and also to fold in the "temporarily shut off magic items" secret rule that was in the 1E DMG. In fact, it doubles down on it, increasing the 1-round duration to 1d4 rounds here. It also does streamline the caster-level check, making it a symmetric +/-5% difference for either higher or lower levels, and thus adjudicating it on a d20.
First, it removes spells and spell-like effects (including device effects and innate abilities) from creatures or objects. Second, it disrupts the casting or use of these in the area of effect at the instant the dispel is cast. Third, it destroys magical potions (which are treated as 12th level for purposes of this spell).
Each effect or potion in the spell's area is checked to determine if it is dispelled. The caster can always dispel his own magic; otherwise, the chance to dispel depends on the difference in level between the magical effect and the caster. The base chance is 50% (11 or higher on 1d20 to dispel). If the caster is of higher level than the creator of the effect to be dispelled, the difference is subtracted from the number needed on 1d20 to dispel (making it more likely that the dispel succeeds); if the caster is of lower level, the difference is added to the number needed on 1d20 to dispel (making it less likely that the dispel succeeds). A roll of 20 always succeeds and a roll of 1 always fails. Thus, if a caster is 10 levels higher, only a roll of 1 prevents the effect from being dispelled.
A dispel magic spell does not affect a specially enchanted item, such as a magical scroll, ring, wand, rod, staff, miscellaneous item, weapon, shield, or armor, unless it is cast directly upon the item. This renders the item nonoperational for 1d4 rounds. An item possessed and carried by a creature gains the creature's saving throw against this effect; otherwise, it is automatically rendered nonoperational. An interdimensional interface (such as a bag of holding) rendered nonoperational would be temporarily closed. Note that an item's physical properties are unchanged: A nonoperational magical sword is still a sword.
Artifacts and relics are not subject to this spell; however, some of their spell-like effects may be, at the DM's option.
Note that this spell can be very effective when used upon charmed and similarly beguiled creatures. Certain spells or effects cannot be dispelled; these are listed in the spell descriptions. [2E PHB, Appendix 3]
The other thing it does is to make more explicit the interrupting counter-spell feature, i.e., "Second, it disrupts the casting or use of these in the area of effect at the instant the dispel is cast." But it still leaves several questions unanswered: Do you cast it and shut down all new magic for a round? Do you "ready" to interrupt, or spontaneously on the fly? Does this presume advance spell declaration and allow for someone to jump in with a declared counter-dispel?
D&D, 3rd Edition -- Now in 3E, the dispel magic text becomes, what, 15 paragraphs long? (But that's not all: see more below):
Dispel Magic... The character can use dispel magic to end ongoing spells that have been cast on a creature or object, to temporarily suppress the magical abilities of a magic item, to end ongoing spells (or at least their effects) within an area, or to counter another spellcaster’s spell. A dispelled spell ends as if its duration had expired. Some spells, as detailed in their descriptions, can’t be defeated by dispel magic. Dispel magic can dispel (but not counter) the ongoing effects of supernatural abilities as well as spells. Dispel magic affects spell-like effects just as it affects spells.
Note: The effects of spells with instantaneous duration can’t be dispelled, because the magic effect is already over before the dispel magic can take effect.The character choose to use dispel magic in one of three ways: a targeted dispel, an area dispel, or a counterspell:
Targeted Dispel: One object, creature, or spell is the target of the spell. The character makes a dispel check against the spell or against each ongoing spell currently in effect on the object or creature. A dispel check is 1d20 +1 per caster level (maximum +10) against a DC of 11 + the spell’s caster level.
If the spellcaster targets an object or creature who is the effect of an ongoing spell (such as a monster summoned by monster summoning), she makes a dispel check to end the spell that conjured the object or creature.
If the object that the character targets is a magic item, the character makes a dispel check against the item’s caster level. If the character succeeds, all the item’s magical properties are suppressed for 1d4 rounds, after which the item recovers on its own. A suppressed item becomes nonmagical for the duration of the effect. An interdimensional interface is temporarily closed. Remember that a magic item’s physical properties are unchanged. Artifacts and creatures of demigod or higher status are unaffected by mortal magic such as this.
The character automatically succeeds at the dispel check against any spell that the character cast.
Area Dispel: The spell affects everything within a 30-foot radius.
For each creature who is the target of one or more spells, the character makes a dispel check against the spell with the highest caster level. If that fails, the character makes dispel checks against progressively weaker spells until the character dispels one spell (which discharges the dispel so far as that target is concerned) or fail all the character's checks. The creature’s magic items are not affected.
For each object that is the target of one or more spells, the character makes dispel checks as with creatures. Magic items are not affected by area dispels.
For each ongoing area or effect spell centered within the dispel magic’s area, the character makes a dispel check to dispel the spell.
For each ongoing spell whose area overlaps that of the dispel, the character makes a dispel check to end the effect, but only within the area of the dispel magic.
If an object or creature who is the effect of an ongoing spell, such as a monster summoned by monster summoning, is in the area, the character makes a dispel check to end the spell that conjured the object or creature (returning it whence it came) in addition to attempting to dispel spells targeting the creature or object.
The character may choose to automatically succeed at dispel checks against any spell that the character cast.
Counterspell: The spell targets a spellcaster and is cast as a counterspell. Unlike a true counterspell, however, dispel magic may not work. The character must make a dispel check to counter the other spellcaster’s spell. [3.0 SRD]
Now, I think that's pretty much the same as the 2E spell; it's mostly just that the 3 sub-effects each got their own section with a thoroughly re-stated version of the effect (thus almost tripling the paragraph count). But at the very end we get to that tricky "counter-spell" implication which has been nagging us all along; be careful what you wish for, because this became its own separate mechanic, with full details in one subsection of the Magic chapter, weighing in at another 7 paragraphs just for that part.
Counterspells: It is possible to cast any spell as a counterspell. By doing so, the character is using the spell's energy to disrupt the casting of the same spell by another character. Counterspelling works even if one spell is divine and the other arcane.
How Counterspells Work: To use a counterspell, the character must select an opponent as the target of the counterspell. The character does this by choosing the ready action. In doing so, the character elects to wait to complete his or her action until the character's opponent tries to cast a spell. (The character may still move at normal speed, since ready is a standard action.)
If the target of the character's counterspell tries to cast a spell, the character makes a Spellcraft check (DC 15 + the spell's level). This check is a free action. If the check succeeds, the character correctly identifies the opponent's spell and can attempt to counter it. (If the check fails, the character can't do either of these things.)
To complete the action, the character must cast the correct spell. As a general rule, a spell can only counter itself. If the character is able to cast the same spell and has it prepared (if the character prepares spells), the character casts it, altering it slightly to create a counterspell effect. If the target is within range, both spells automatically negate each other with no other results.
Counterspelling Metamagic Spells: Metamagic feats are not taken into account when determining whether a spell can be countered.
Specific Exceptions: Some spells specifically counter each other, especially when they have diametrically opposed effects.
Dispel Magic as a Counterspell: The character can use dispel magic to counterspell another spellcaster, and the character doesn't need to identify the spell he or she is casting. However, dispel magic doesn't always work as a counterspell. [3.0 SRD]
In summary: The caster must "ready" an action to counter-spell, naming one specific enemy as a target, sacrificing any action in exchange for the opportunity to counter the enemy in the event they cast during the round. This counter is automatic if the same or antithesis spell is used against it (i.e., haste vs. slow), or at the usual check if dispel magic is used. In practice, I found this minimally useful given the rules bloat -- occasionally it would be a good idea if there was just one obviously powerful enemy caster, and the party caster didn't have much to do other than try and shut them down. It would be a marginally more useful mechanic if the counter-speller didn't have to identify one particular enemy character in advance.
Moldvay Basic D&D -- Looking at the Basic D&D line, dispel magic does not get detailed in Holmes Basic D&D (although it appears in a table listing 3rd-level spells, "to give some idea of the range of magical possibilities"). Moldvay Basic does present the details, as 1 of just 3 such spells given in case higher-level NPCs are desired by the DM. It says this:
Dispel Magic: Range 120', Duration: permanent. This spell will remove spell effects anywhere within an area 20'×20'×20', and may be cast up to 120' away from the caster. It will not affect magic items, but will remove any spell effect created by a magic-user, elf, or cleric of an equal or lower level than the spell caster. It may fail to remove magical effects from a higher level caster. This chance is 5% per level of difference between the spell casters. EXAMPLE: A 5th level elf trying to dispel magic cast by a 7th level elf would have a 10% chance of failure. [Moldvay Basic, p. B18]So that's based on the OD&D text, but the phrasing is pretty much totally rewritten. Given that, it's simple, short, clear, cohesive, and easy to remember. Once again Moldvay waves the flag of victory on the issue.
Commentary -- At it's core, dispel magic can be a pretty simple piece of game magic: it's a spell-be-gone effect. The complications are primarily side issues. First, the implied possibility of an interrupting "counter-spell" comes more and more into focus across editions 0, 1, 2, and 3. Second, the possibility of temporarily shutting down magic items gets mixed in there with 1E, and maintained and extended in 2E and 3E. On the other hand, Moldvay simply eliminates both these side issues, and therefore has a body of text about 5% as long as 3E for the effort.
The other thing that varies is the exact chance of succeeding or failing with a dispel magic, which is actually never exactly the same between any two editions of D&D you can pick. (Note in particular the novelty of OD&D, where you're supposed to divide the dispeller's level by the original magic-user's, generating oddball percentages and likely requiring a calculator; e.g. 5th vs. 7th level is 71.4285...% to succeed.) To highlight this I present the chart below:
|Edition||Dispel Check Rule||10th vs. 5th||10th vs. 10th||5th vs. 10th|
|CM||2d6, need 7, +1/rank higher||58%*||58%*||8%*|
|OD&D||Ratio of dispeller to original caster||100%||100%||50%|
|1E||50%, +5%/higher, -2%/lower||75%||50%||40%|
|2E||50%, +5%/higher, -5%/lower||75%||50%||25%|
|3E||50%, +5%/higher (max 10), -5%/lower||75%||50%||25%|
(* Estimate equating 5th level to the lowest type, and 10th level as the highest type described.)
Which of these bases is best? You could go in a couple directions with that. Perhaps equal-level wizards trading a spell for a spell should automatically succeed and be balanced in that regard (i.e., 100% at equal levels); and given the two options, the Moldvay mechanic is so much simpler it's the clear choice. On the other hand, I do like the interactivity of opposed caster-level checks (i.e., 50% at equal levels), which is what I currently have in place in my Book of Spells and seems to work quite well in my recent games. So I'll probably stick with that.
That said, the side-complications of possibly affecting magic items, et. al., that got mixed into the Advanced line seems like a really bad case of rules-bloat. Give me the brevity, memorability, and playability of Moldvay any day over that stuff. What say you?