Article: Memory, RAM, ROM, flash
The amount of memory a phone has can actually result in multiple, different answers, and to make things harder a lot of web sites confuse the different types. In general, these are the types of memory a phone can have:
* ROM: This is non writable memory, containing the basic operating system of the phone. When you do a hard reset and format the memory of the phone, what's on the ROM is what stays and why your phone can always be reset to factory settings. The amount of ROM a phone has is irrelevant since you can't add things to it.
* Flash / internal memory: The amount of internal memory, or flash memory, is the space inside the phone where programs reside and where you can store messages, contacts and files. It's usually the number you see when you look at a phone description and it says, for example, that the Nokia 6620 has 12 Megs of memory. Note that if you are trying to save data such as a game on your phone and your phone complains about memory issues, this is probably what it needs.
* RAM: This is the temporary memory used to run programs. It must not be confused with the flash, since it can't be used to store data. The memory is cleaned every time the phone is turned off. This is very rarely written in descriptions, but it's very important since it dictates how many programs you can run at once. Some tools can tell you the number, such as FExplorer for S60 phones. The 6620 has 26 Megs. Note that when trying to run a program, if it complains of memory issues, this is what it needs.
* External memory: This is simply the external flash memory cards that can be added to the phone. Many phones have extension slots now, but you need to be aware of the maximum size they support (128 Megs, 512 Megs, 1 Gig and so on), and also the type (MMC, RS MMC, MiniSD, and so on). There are not a lot of differences between the various types other than physical size and power consumption. Some recent models also introduced some DRM (copy protection) capacities.
When shopping for a phone, especially a smart phone, it's important to have all the numbers. For example a Nokia 6682 has less RAM than a 6620, and will have more problems running multiple applications. Finally one last type of memory you may encounter is SIM memory for GSM phones. This is simply a very tiny amount of memory on your SIM card to store contacts and messages. The only benefit is that it stays with your SIM instead of in the phone.