What does Prim mean?

[gloria200116]

Since joining second life, I have seen that word a lot but still haven't found what it means.

[Rhonda Huntress]

It is short for primitive.  It is a basic building block that can be created and manipulated to form complex objects. 

[Theresa Tennyson]

It's also used as a shorthand term for a unit of "land impact", which is the measure of how many objects of what type can be on a piece of land. Originally each basic building block had a land impact of 1 so the number of items your land could hold was directly based on the number of primitives making up those objects. A few years ago land impact calculations were made more specific but some people still use "prims" to stand for land impact, in the same way my father calls the refrigerator the "icebox."

[Prokofy Neva]

It's the elements of things, like a table might have 5 prims or a chair might have 2 prims. You only get so many of those little building blocks making up stuff per land parcel, you can read the numbers on the "About Land" menu.

It used to be, everything in Second Life was made out of prims. Then they added "sculpties" to make things with soft edges. Then they added "mesh" to give even more realism.

Once they started mesh, they started another term, "land impact" to mean what everything is taking up on your land. "Land impact" and "prims" can be the same, or different, sometimes by a small number, rarely by more. Usually I find "Land Impact" is about the same as "prims".

[Phil Deakins]

To make things absolutely clear to you, get yourself on a piece of land where you have right to rez objects. Your own land, or a sandbox will do. Right click the ground or a surface, and click Build. The Edit box opens but ignore it. Then left click the ground or surface and a wooden cube will appear on the spot where you clicked. That's a prim (primitive).

When you clicked Build, the Edit box opened in which you can chose the shape of the prim you create. The default is the cube.

By changing the dimensions, and other things about the prim (using the same Edit box), and then, by linking a number of them together, and putting textures on various surfaces, you can create useful objects.

To link prims together, select the ones you want to link by right clicking one and clicking Edit. You'll see that the prim is highlighted with a yellow border. Then, while holding the Shift key down, left click the other prims that you want to link to it. They too acquire the yellow border. When you have them all highlighted, click the Link button in the Edit box. Now move one of the prims. They all move together. They are linked. They don't need to be touching to be linked together. You can imagine how objects are made from a number of suitably shaped prims, all linked together.

That was how all objects used to be made, and many are still made that way. With the advent of sculpties, and then mesh, objects became makeable by using an external programme to create different shapes to the standard cube, sphere, etc. ones. If, for instance, the shape of a table is made and uploaded, it's only 1 prim, and there is no need to link it to any others. Because the size of a parcel of land dictates how many prims can be rezzed on it, this was a huge bonus. Instead of a table using 5 prims from the land's allowance, for instance, it only needed to use 1.

That was the period of 'sculpties', but then mesh came along and changed things. Mesh is like sculpties, in that the shape is created externally and uploaded to SL, so the same table can be made externally and still only use 1 prim. But there's a difference. Along with mesh came Land Impact (LI). Instead of calculating how many prims are rezzed on the land, the system now calculates how much impact an object has on the serverside resources. Land no longer supports a set number of prims according to the size of the parcel. Instead it supports a set number of Land Impact (LI) according to the size of the parcel.

All objects are set as 'prim' or 'convex hull'. Convex hull applies to all mesh objects. When an object is set as 'prim', the LI is 1 per prim used in the object. When it is set as convex hull, the LI is calculated by the system, and can be quite heavy. So the 5 prim table can use up more than 5 LI.

A big advantage of changing from prims per parcel to LI per parcel is that objects made from standard prims can also be set as convex hull, with the result that the number of LI is reduced - often halved - which means that a parcel of land can support a lot more prims that it did before mesh came along. Extreme example: a 512m parcel of land supports 175 LI. If all the objects on the parcel are made from regular prims, and if they are all objects that link prims together, and if all the objects contain an even number of prims (2, 4, 6, etc.), and if no scripts, or some very small scripts, are in the objects, then the 512m parcel can support 175 x 2 prims, which = 350 prims, in its 175 LI allowance.

Edited October 24, 2017 by Phil Deakins

[redhuskycjr17]

While others explained what a prim is, i add some addition to it.

Changing an object Physics Shape Type to reduce land impact might also change the object behavior. 

Example i have an mesh wall with center hole for a door. When the object is set to prim, it allows you to pass but when set to convex, it behaves likes its a full wall, even if it has a hole in it for a door, you cant pass. 

Scripts, textures, size ect can affect the land impact. Not only that, but also linking or unlinking a mesh can cause instantly the land impact to rise up to ~300 LI or more. And yes, that will cause the region to return objects if it rises too much