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Memory is now one of the largest sectors within the semiconductor industry. A memory IC is a digital IC that holds information; it acts as storage space for the device it is used in. Memory is essential to most systems so that it can store information either during a complex calculation or for later retrieval. The memory is stored in binary format, which means that each bit, or piece of memory, is either a 1 or a 0. There are many different kinds of memory IC, each with a different function within the system. The two main categories of memory are "volatile" and "non-volatile." Ordinarily, volatile memory is also called "random access memory" (RAM) and non-volatile memory is referred to as "read-only memory" (ROM). Volatile memory means that it requires constant electrical input to maintain its current state, i.e., the information it is holding; once the power is switched off, the memory is lost. Non-volatile memory, on the other hand, keeps the information after the power is switched off. It does this via solid state techniques, e.g., by storing the information using magnetic or optical means rather than electrical.
Dynamic RAM (DRAM)
This is the most common type of RAM used in computers and workstations today. It stores bits of information using a capacitor and transistor unit. This memory unit needs to be refreshed every few milliseconds (hence the term "dynamic") by a burst of electricity as capacitors lose charge or "discharge" once the electrical input is removed. Refreshing keeps the capacitors charged to the correct level as is needed for the information it is holding.
Flash Memory
This continues to be the star of the memory industry. Designers have managed to combine the burst and fast page techniques into the flash framework. AMD and Intel are the main competitors in the flash memory segment. Among developments from both companies, the following features are boasted: lower power consumption, embedded algorithms to erase a combination of designated sectors, multi-package options, pause/resume erase functions, and many more. 64Mbit memory units are becoming rapidly available and both companies have launched 128Mbit and 256Mbit units by the end of 2002. There are two major technologies of flash memory: NOR and NAND:
NOR Flash
This is named after the specific data mapping technology (Not OR). NOR flash memory provides high-speed random-access capabilities, being able to read and write data in specific locations in the memory without having to access the memory in sequential mode. Unlike NAND flash, NOR flash allows the retrieval of data as small as a single byte. NOR flash excels in applications where data is randomly retrieved or written. NOR flash is most often found built into cellular phones and PDAs and is also used in computers to store the start-up.
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