RAM is how your computer opens, reads, and runs the PC software and games you use. RAM modules are often measured in megabytes (MB) and gigabytes (GB). In terms of memory, 1024 MB equals 1 GB, so 512 MB of RAM is half as much as 1 GB. What this distinction means for your computer depends on certain considerations.
Memory type plays a big role in determining the difference between 512MB and 1GB RAM. For example, DDR3 PC3-12800 RAM has a maximum transfer rate of 12.8 GB per second, while DDR PC-1600 memory can only transfer 1.6 GB of data per second. Since DDR3 PC-12800 RAM is much faster, 512MB of extended DDR3 memory is still better than 1GB of the older, slower DDR PC-1600 memory.
Operating system requirements
The operating system you are using requires a certain amount of memory to work properly on your computer. The higher this requirement, the less RAM you will have to run other software. For example, Windows XP only requires 64MB of RAM, so even if you only have 512MB, you can still open and run other software. Windows 7, on the other hand, requires at least 1 GB. With Windows XP there is not much difference in terms of the operating system, but with Windows 7 you just can't run it with 512 MB of RAM, but with 1 GB.
Age and usage
The age of your computer and hardware also determines how much difference 1GB of RAM makes over 512MB. New computers that use dual- or triple-channel technology can read memory better and faster than computers without that technology, which means that 1GB of RAM can go much further in a new system if it's set up correctly. Many older programs and operating systems have lower RAM requirements, which means that 512MB on a computer using older programs will go much farther than on a Windows 7 computer with the latest resource-intensive software.
Virtual memory size
Virtual memory is the space on your hard drive that your computer uses to simulate additional RAM. The more virtual memory your system uses, the larger the RAM will be. Virtual memory is mainly used to store open programs when you are not directly using them to make room for on-demand programs to use your RAM. Since virtual memory is mostly used only when needed, 512MB of real RAM and 2.5GB of virtual memory provide better performance than 1GB of real RAM and no virtual memory, since a 1GB system has absolutely no backup capability when all the real RAM is in use.