Damage types

StarCraft
In StarCraft, there are three damage types: concussive, normal, and explosive. The actual damage done depends on the type and the size of the target unit, as indicated in the following table:

Protoss shields always take full damage.

Concussive Damage
Units which deal concussive damage are optimized to kill small units such as zerglings and zealots. Concussive damage is limited more than any other damage type and is comparatively a rare attack mode.

It includes the vulture, ghost and firebat.

Concussive damage, like all damage types, always does full damage against protoss shields.

Explosive Damage
Units which deal explosive damage are optimized to kill large units and buildings. Explosive damage isn't particularly limited against small units (which suffer half of the damage). Despite the name, many explosive attacks do not deal splash damage; for instance, the siege tank's attack in tank mode is optimized for destroying armored units, but it only gains splash damage when it switches to siege mode.

Explosive damage always deals full damage against protoss shields.

It includes all rockets attacks (e.g. missile turrets, goliaths, scouts), and every type of powerful cannons, like the s, and dragoon ones.

Normal Damage
Normal attacks are effective against all type of units.

It includes all melee attacks, like those of the zergling and ultralisk. It also includes laser weapons (battlecruiser), most bullets (marine) and special cases (photon cannon, workers' attacks)

Unit Sizes
Unit size is only loosely correlated with the size of a unit's sprite and the amount of space a unit takes up in a transport. Unit size is more closely linked to armor quality.

A small ground unit, such as a ghost, wears personal armor, whereas a large unit, such as a, is covered with neosteel plating. Few units, such as the hydralisk, are medium-sized.

Most air units are large; indeed, all terran air units are large, even units which would be expected to be relatively small and lightly-armored, such as Wraiths (compared to battlecruisers). Most powerful anti-air attacks deal explosive damage, as a result. The biggest exception to the rule is probably the mutalisk, which is small, but is expected to face explosive attacks regularly. (Mutalisks do low damage, however).

StarCraft II
In StarCraft II, units deal a base amount of damage and may gain a bonus against certain armor types. For instance, the missile turret gains a bonus against medium units and a larger bonus against armored units. Damage is added on a "per hit" basis, and bonuses are calculated before armor is subtracted.

Unit armor types (as of September 2008) are light and armored. Buildings are treated as armored and have the "structure" property.

Attack types are more varied than in StarCraft I, and can gain bonuses towards light, armored, biological, massive and even psionic units.

Shields are generally not subject to bonus damage. Instead, certain units do bonus damage against shields.

Development
Shields were not subject to the same bonus damage as the unit underneath them in January 2008.