Mobile Frame Systems make up both the equipment/abilities of a mobile frame as well as the number of additional hits that frame can take.
When a frame attacks, you can use either a red die or, if it's higher, one of your white dice. A single weapon system gives a frame two red dice. A weapon only works at one range, so using it involves a gamble. You can pair two weapon systems at a range to make it more powerful granting a bonus red d8 die; this allows attacks at this range to roll two red d6s plus a red d8, choosing the highest result. You can split it across ranges (such as a pistol that is worth one die at Hand-to-hand range and another at direct range. You can also split a double weapon, like a rifle with a bayonet that gets 3 dice at direct range and 1 at hand-to-hand.
For instance, you might describe weapons as being (2Rd) for a regular rifle that works at direct range, (2Rh) for a combat knife that works at HtH range, (2Ra) for a rocket launcher that works at artillery range.
When you combine them, you can describe them as being, for instance, (2Ra+d8) for the double artillery cannon in Estar's Anvil or (3Rh+1Rd) for a grapnel that works great at hand-to-hand range but not as well at direct range.
Hand-to-hand weapons do approximately twice as much damage as ranged weapons, as their wielders know up close where and how to hit their target.
Sensors & CommunicationEdit
Any system used to sense, command, or communicate gives your frame a yellow die. When a frame spots, you can use a yellow die or, if it's higher, one of your white dice. Because spotting enhances attacks on a particular target directly, you'll find that these systems are critical to a company's success. While any frame can spot another in plain sight, only those with yellow dice can spot another in cover. If a frame has two yellow dice, it can spot anywhere on the table.
Main Source: Mobile Frame Zero: Rapid Attack Rulebook