As cellphones get smarter, their similarity to PCs becomes closer. Even the most unassuming mobile has both ROM and RAM; in 2011, the amounts in smartphones rival those of laptop computers. A phone is put together differently than a PC, however. Its long-term memory needs are different, and it uses more ROM than RAM.
A desktop or portable computer has several kinds of memory. It uses RAM for open documents and programs, ROM for built-in programs, hard drives for bulk storage and DVD-ROM for removable storage. A cellphone, by comparison, has no hard drive or DVD-ROM. It depends entirely on its RAM and ROM for data storage.
RAM is fast, moving data at the rate of millions of data characters per second. It's also inexpensive and can be read and written to an unlimited number of times. When you turn the power off, however, RAM loses its data, so you can't use it for long-term storage. RAM acts as a phone's scratch pad, holding programs, intermediate results and other short-term data. Smartphone models such as the iPhone 4 and Galaxy S have 512MB of RAM. A typical PC as of 2011 has from 1GB to 4GB of RAM. The gap between desktop PCs and mobile devices is closing; in 2007, a typical smartphone had 64MB of RAM.
Unlike RAM, ROM retains its data even without power, so it serves as a smartphone's long-term storage. It has a limited ability for accepting new data, however. The earliest ROM chips, first produced in 1965, received their programming at the factory, and it was permanent. Newer generations of ROM readily receive new programming, though mainly a cellphone doesn't write to it.
A newer type of memory, known as flash, blurs the distinction between RAM and ROM. Like ROM, flash keeps its data when the power is off. You can overwrite data on flash millions of times -- still not as much as RAM, but more than traditional ROM. With improving technology, the capacity of flash chips rivals that of hard drives. Flash offers storage capacities of over 30GB for cellphones, allowing you to save music libraries, movies and other sizable content.