When it comes time to upgrade the RAM in your machine, it’s often a cause of confusion—the question we usually hear is “will this wipe all my data?” As many of you tech gurus know, the short answer is no, it will not.
The long answer is no, because your data is not stored in RAM. The operating system, applications, your documents, pictures, and movies are all stored on the hard disk. The difference is important: a hard disk is (historically) a series of rotating platters that store data magnetically, and accesses this data through a read/write head similar to a record player. RAM (Random Access Memory) is used for temporary storage while your computer is running.
Any time you launch an application, it is copied to RAM for faster access. When you load a document, it is copied to RAM as well. This is why you have to be sure to save your work from time to time—if something were to happen like a power failure, you would lose everything in RAM since RAM is cleared every time you shut down your system. (Note that RAM is not erased when your system goes into “sleep mode.”)
The main purpose of RAM is to run applications. The more RAM you have, the more applications you can run at once. If you start to run low on RAM, then the operating system will start to swap out data to a space on the hard disk. This space is called a cache; Windows used to call it a swap drive. For example, if you have four applications running and try to launch a fifth, OS X will take whichever application you’re using the least often and put its data into the cache on the hard drive to make room for the new application.
This is why occasionally you will switch to an application and it takes a few seconds to bring it up—the OS is copying data from RAM to the cache to make room for the application you selected, then it copies the data from the cache back to RAM. Adding more RAM means you can have more applications running so this swapping doesn’t happen as often. Most of the time this swapping is not too noticeable, but when you are dealing with large data files then it can show the infamous spinning beach ball.
The hard disk, on the other hand, is where all your applications and data live. If you were to upgrade to a larger hard disk, then yes, your data would be gone unless you transferred it over. Changing out the RAM has no effect on the contents of the hard disk.
I used the word “historically” earlier because up until the past few years, a hard disk was just that—a solid disk. In the last few years, a new technology has hit the market, called a Solid State Drive (SSD.) There is no spinning disk involved; instead it uses flash memory that is similar to RAM but does not lose its data when the system is powered down.
It works similarly to a USB thumb drive—you can copy data to and from it, and it is retained when the drive is unplugged. SSDs are faster than hard disks, but don’t quite match up in terms of price and capacity. As an example, a 320GB hard disk for a notebook computer goes for about $110. A comparable SSD costs about $460 for a 240GB drive. A 1TB hard disk is about $140, whereas a 1TB SSD would set you back about $3700. Might wipe out your bank account, but your data is safe!