Difference Between RAM and ROM

Definition RAM and ROM

RAM - Random Access Memory:

                   RAM (pronounced ramm) is an acronym for random access memory, a type of computer memory that can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes. RAM is the most common type of memory found in computers and other devices, such as printers.

Types of RAM

There are two different types of RAM:

• DRAM (Dynamic Random Access Memory)
• SRAM (Static Random Access Memory).

The two types of RAM differ in the technology they use to hold data, with DRAM being the more common type. In terms of speed, SRAM is faster. DRAM needs to be refreshed thousands of times per second while SRAM does not need to be refreshed, which is what 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 so much more expensive. Both types of RAM are volatile, meaning that they lose their contents when the power is turned off.

ROM (Read Only Memory):

ROM is a type of "built-in" memory that is capable of holding data and having that data read from the chip, but not written to. Unlike Random Access Memory (RAM), ROM is non-volatile which means it keeps its contents regardless if it has power or not. A good example of ROM is EEPROM, which is a programmable ROM used for the computer BIOS, as shown in the example picture to the right.

        The term ROM is used to describe any type of memory or media that is read only. For example, a CD-ROM (Compact Disc Read-Only Memory) is a disc that can only be read from and a drive only capable of reading.

RAM, Main Memory and ROM Explained:

In common usage, the term RAM is synonymous with main memory, the memory available to programs. For example, a computer with 8MB RAM has approximately 8 million bytes of memory that programs can use. In contrast,ROM (read-only memory) refers to special memory used to store programs that boot the computer and perform diagnostics. Most personal computershave a 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 RAM.

What is the difference between ROM and RAM?

                       There is one major difference between a ROM chip and a RAM chip.

                       A ROM chip does not require a constant source of power to retain the information stored on it, whereas a RAM chip does require a constant source of power to retain the information. When a computer is turned on, and programs are being run, the programs information is stored in the RAM chip for better efficiency and speed. However, as soon as the computer is turned off any information stored in the RAM chip is lost. With a ROM chip, any information stored on the chip remains on it with or without power.

                 ROM chips are commonly used in gaming system cartridges, like the original Nintendo, Gameboy, Sega Genesis, and a number of others. The game cartridge stores the game programming on a ROM chip which is read by the game console when the cartridge is inserted into the console.

                         ROM chips can also be found in computers, to store the programming needed to begin the initial boot up process when turning on a computer. Using non-volatile storage is the only way to begin the start up process for computers and other devices that use similar a start up process. The most common type of programmable ROM (PROM) chip in a computer is the BIOS.

                        RAM chips are also used in computers, as well as other devices, to store information of the programs currently running on the computer. However, only volatile information can be stored on RAM chips, due to that fact that if power is lost to the computer all information stored in the RAM is lost.

                       The oldest ROM-Type storage media can be dated back to 1932 with drum memory. Today, ROM-Type storage media is still used and continues to be improved upon for better performance and storage capacity.