Riddle de de

Soldiers line up spaced with pride,
Two long rows lined side by side.
One sole unit can decide,
If the rows will unite or divide.
Tell me, tell me, scream it out.
What's the thing I talk about?

It's Time for a Tuesday Riddle

When I was young, I occupied an entire room...
And now, after so many decades, I can fit even in your pocket!

What am I?

Very Hard Riddle

Almost everyone makes it in but not many make it out.

What is being alluded to here?