The memory chip, with the controller chip, is the most important element of a memory card. The memory chip is based on the flash memory technology which is solid-state, non-volatile and rewritable. Solid-State means it contains no moving parts and therefore is immune to mechanical failures and damages from movements and vibrations. It also operates completely silent with a zero decibel noise level. Non-Volatile flash memory stores bits of information in memory cells made of silicon wafers which do not require power to retain information when power is turned off.
In general flash memory functions like RAM memory and a hard disk drive combined. It stores digital data in memory cells like the RAM memory, and stores information like a hard disk drive when the power is turned off. In comparison to other storage media flash memory offers superior features such small form factor, high degree of durability, high degree of reliability, low power consumption and high transfer speed. Based on that flash memory technology is ideal for use in memory cards. The only disadvantage is the manufacturing cost, which is higher compared to hard disk drives, CDs and DVDs.
There are two different technologies of flash memory, NOR and NAND. NAND flash memory is ideal for memory cards because is less expensive and can accommodate more storage capacity in the same die size. Memory card manufactures are using different NAND technologies for either boasting the memory card’s performance or for decreasing the memory card’s manufacturing costs. The most common flash memory technologies are the Single-Level Cell, Multi-Level Cell, Multi-Bit Cell and Chip Stacking. The Single-Level Cell technology is used to boast the memory card’s performance while the rest are used for decreasing manufacturing costs. The most used technology of them all is the Multi-Level Cell.
A Single-Level Cell, SLC, memory card stores one bit in each cell, leading to faster transfer speeds, lower power consumption and higher cell endurance. The only disadvantage of Single-Level Cell is the manufacturing cost per MB. Based on that, the SLC flash technology is used in high-performance memory cards.
A Multi-Level Cell, MLC, memory card stores three or more bits in each cell. By storing more bits per cell, a Multi-Level Cell memory card will achieve slower transfer speeds, higher power consumption and lower cell endurance than a Single-Level Cell memory card. The advantage of Multi-Level Cell memory card is the lower manufacturing costs. The MLC flash technology is used mostly in standard memory cards. The Multi-Bit Cell, MBC, is a similar technology to the Multi-Level Cell but stores only two bits per cell.
Chip stacking technology is used by many manufactures to double the memory card’s capacity at considerable lower manufacturing costs. This is achieved by putting two chips together to form a single chip. For example, by stacking two 256 MB chips together they will form a single 512 MB chip. This technology is far less expensive alternative to the single-die chips or even called monolithic chips.
|
