How a server use same memory for every request?

Question

I am working on a PHP project and asked to implement a system (runs on server) which uses same memory location for every request.

To be simpler, think that there is an array in the memory (RAM) and every client ask for one element of it. Server does not create that array repeatedly. To achieve it, server must use a shared memory and returns the related elements to the clients. The question is, how can I do it? Or is there any source explaining it.

Constraints:

1. I don't want to use applet technology. And as much as possible, I want to implement it via PHP.
2. I don't want to use a database since it is too slow for our system and our data does not require to be persistent for any system down.
3. Data is really small (does not exceed 10MB) and fits to the memory.