output buffering in php

Output Buffering

Without output buffering (the default), your HTML is sent to the browser in pieces as PHP processes through your script. With output buffering, your HTML is stored in a variable and sent to the browser as one piece at the end of your script.

Advantages of output buffering for Web developers

• Turning on output buffering alone decreases the amount of time it takes to download and render our HTML because it's not being sent to the browser in pieces as PHP processes the HTML.
• All the fancy stuff we can do with PHP strings, we can now do with our whole HTML page as one variable.
• If you've ever encountered the message "Warning: Cannot modify header information - headers already sent by (output)" while setting cookies, you'll be happy to know that output buffering is your answer.

List vs Array

List vs Array

List is dynamic size and array is fixed size.

If You can add new elements to a list, but to add a new element to an array you need to create a new larger array and copy the old elements.

Arrays are a little leaner and more efficient if you don't need dynamic resizing, but lists are usually more convenient and the performance difference rarely matters for most applications.

For more information. 

http://stackoverflow.com/questions/434761/array-versus-listt-when-to-use-which