Random Access Memory (RAM)
Random access memory (RAM) is a form of computer data storage. A random access device allows stored data to be accessed in very nearly the same amount of time for any storage location, so data can be accessed quickly in any random order.
RAM is often associated with volatile types of memory (such as DRAM memory modules), where its stored information is lost if the power is removed. The first RAM modules to come into the market were created in 1951 and were sold until the late 1960s and early 1970s.
Read-Only Memory (ROM)
Read-only memory (ROM) is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware (software that is very closely tied to specific hardware, and unlikely to need frequent updates).
Other types of non-volatile memory such as erasable programmable read only memory (EPROM) and electrically erasable programmable read-only memory (EEPROM or Flash ROM) are sometimes referred to, in an abbreviated way, as “read-only memory” (ROM); although these types of memory can be erased and re-programmed multiple times, writing to this memory takes longer and may require different procedures than reading the memory.When used in this less precise way, “ROM” indicates a non-volatile memory .
A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations. As long as most memory accesses are cached memory locations, the average latency of memory accesses will be closer to the cache latency than to the latency of main memory.