There are two types of RAM
1) DRAM (Dynamic Random Access Memory)
2) SRAM (Static Random Access Memory)
The two types differ in the technology they use to hold data, with DRAM being the more common type. In term of speed SRAM is faster. DRAM needs to be refreshed thousands of times per second while SRAM does not need to be refreshed, which makes it faster than DRAM. DRAM supports access times of about 60 nanoseconds, SRAM can give access times as low as 10 nanoseconds. Despite SRAM being faster, it's not as commonly used as DRAM because it's more expensive. Both types of RAM are volatile, meaning that they can lose their contents when the power is turned off.
In common usage, the term RAM is synonymous with main memory, the memory available to program.
For Example, a computer with 8MB RAM has appromximately 8 million bytes of memory that program can use. In contrast, ROM (read-only memory) refers to special memory sed to store program that boot the computer and peform diagnostics. Most personal computer have small amount of ROM ( a few thousand bytes) In fact, both types of memory (ROM and RAM) allow random access. To be precise, therefore, RAM should be referred to as read/write RAM and ROM as read-only memory RAM
