Flash memory technology is used for many forms of electronic data storage.
Flash memory is a non-volatile form of electronic data storage and as a result it is used in many areas where short and medium term data storage is needed.
Flash memory technology is visible in many forms: everything from the familiar flash memory sticks and camera memory cards, right through to applications in replacing computer hard drives where it is much faster and lighter.
What Is Flash memory?
Flash memory storage is a form of non-volatile memory that was born out of a combination of the traditional EPROM and E2PROM.
In essence it uses the same method of programming as the standard EPROM and the erasure method of the E2PROM.
One of the main advantages that flash memory has when compared to EPROM is its ability to be erased electrically. However it is not possible to erase each cell in a flash memory individually unless a large amount of additional circuitry is added into the chip. This would add significantly to the cost and accordingly most manufacturers dropped this approach in favour of a system whereby the whole chip, or a large part of it is block or flash erased - hence the name.
Today most flash memory chips have selective erasure, allowing parts or sectors of the flash memory to be erased. However any erasure still means that a significant section of the chip has to be erased.
How Flash memory works
The technology used to manufacture flash memories is based on EEPROM (electrically erasable programmable read-only memory) chips, which consist of memory banks formed of storing cells disposed in a grid of columns and rows.
. . . . Read more about how Flash memory works.
Flash memory reliability and life
When Flash memory was first introduced it had a relatively short lifetime. The repeated use of the cells caused the memory to degrade. As such Flash memory was only used for a restricted number of read / write cycles.
Nowadays Flash memory technology ahs been significantly improved and reliability is not the issue that it was. Nvertheless Flash memories to incorporate a scheme of what is termed wear levelling to reduce the impact on cells or areas of the memory that may be subject ot high use.
. . . . Read more about Flash memory life and reliability.
Flash memory advantages & disadvantages
As with any technology there are various advantages and disadvantages. It is necessary to consider all of these when determining the optimum type of memory to be used.
Flash Memory Advantages
- Non-volatile memory
- Easily portable (e.g. USB memory sticks, camera flash cards, etc)
- Mechanically robust
Flash Memory Disadvantages
- Higher cost per bit than hard drives
- Slower than other forms of memory
- Limited number of write / erase cycles
- Data must be erased before new data can be written
- Data typically erased and written in blocks
Obviously when considering the use of Flash memory in any partciuar application, it is necessary to weigh up the advantages and disadvantages.
Flash memory types
There are two basic types of Flash memory. Although they use the same basic technology, the way they are addressed for reading and writing is slightly different. They two flash memory types are:
- NAND Flash memory: NAND Flash memories have a different structure to NOR memories. This type of flash memory is accessed much like block devices such as hard disks. When NAND Flash memories are to be read, the contents must first be paged into memory-mapped RAM. This makes the presence of a memory management unit essential.
- NOR Flash memory: NOR Flash memory is able to read individual flash memory cells, and as such it behaves like a traditional ROM in this mode. For the erase and write functions, commands are written to the first page of the mapped memory, as defined in "common flash interface" created by Intel.
NAND / NOR tradeoff: NAND Flash memories and NOR Flash memories can be used for different applications. However some systems will use a combination of both types of Flash memory. The NOR memory type is used as ROM and the NAND memory is partitioned with a file system and used as a random access storage area.
Flash memory is a particularly important form of semiconductor memory. It is now widely used and is possibly one of the most important forms of medium term storage. As mentioned earlier Flash memory can be seen in a variety of forms and uses ranging from Flash memory USB sticks to Compact Flash cards used for cameras. In addition to this many other items of electronics can be seen using Flash memory ranging from mobile phones to MP3 players and many more. In view of its current importance, Flash memory will be seen in widespread use for many years to come.
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