Why has the free space on my ssd shot up ?



I recently installed an SSD into my computer, and i installed Windows 7 onto it. After installing a few other programs that I wanted to run faster I had around 4Gb of space left over. (I had a 60Gb SSD)

2 days ago I noticed that I had 16Gb of space available. don't get me wrong, I'm not complaining, obviously, I'm just curious as to why this has happened. I haven't removed anything from it at all, and the only programs that I have installed that could possibly alter anything are Norton antivirus and Advanced System Care 5.

Please can anyone tell me why this has happened?

For those who are interested, below are my system specs:

CPU - AMD FX-8120 8 core (stock clock speed: 3.1Ghz, overclocked to 4.5Ghz)

GPU - Nvidia GeForce GTX 550Ti 2Gb

RAM - 16Gb Corsair Vengeance (1600Mhz)

HDD - 1Tb 7200Rpm

SSD - 60Gb Corsair Agility 3

PSU - Corsair CX600 600Watt

CPU Heatsink - Zalman CNPS 9900NT