Specifications

16
gives up to NOR logic in quick random access. NOR logic chips are used for applications using binary code
rather than memory, such as a computer’s BIOS or a device’s firmware.
* These erase cycles do not mean that the devices can only be accessed or changed 100,000 or 10,000 times. A “wear
leveling” feature in flash memory distributes the changes in the memory cells to prevent some cells from seeing changes
all the time while other cells are ignored. Wear leveling distributes the changes around the cells so that they all approach
the 100,000 or 10,000 cycles uniformly.
USB memory drives have been growing in popularity because of their usefulness and simplicity.
Unlike flash cards with their confusing array of shapes and sizes that determine their application,
USB drives use the universal USB connection as their standard connection and use their multiple
shapes and sizes for as expressions of style. USB drives are, in fact, merely flash cards with a
standard connection that makes them easy to use.
FLASH CARDS
The first cards on the market were PCMCIA cards named for the Personal Computer Memory Card
Industry Association that set the standards for these cards. These cards come in three types of
increasing thickness for different applications: Type I is 3.3 millimeters; Type II is 5.0 mm; and
Type III is 10.5 mm. The Type I cards can fit into Type III slots, but the reverse is not true because
of the greater thickness of the Type III card. Laptop computers immediately adopted these storage
devices because of the advantages of flash memory in terms of capacity, small size, erasable and
non-volatile memory, and low power consumption. The PCMCIA or “PC” cards were an immediate
hit, and development work began on other designs that would incorporate the same advantages
with other additional features, particularly smaller sizes. The results are a variety of flash memory
cards and, perhaps, more confusion than is necessary.
COMPACT FLASH
In 1994 the Compact Flash appeared as a smaller alternative to the PCMCIA card. It was one-
fourth the volume of the PC card with only 50 contact pins instead of the PC card’s 68 pins, but it
used the same type of connecting slot. There are two versions of the CF card: Type I, the more
common version, with a thickness of 3.3 millimeters; and Type II, with a thickness of 5.0 mm. Like
NAND Flash
•Transistors arranged in series
•Software allows devices to work similarly to disc
drives.
•Erase cycles: 100,000 for SLC; 10,000 for MLC*
•faster write and erase times
•greater data density and capacity
•less expensive than NOR
•USB Drives and Flash Cards
NOR Flash
• Each transistor stands alone.
• Works as internal memory with fast random
access to any location
• 100,000 erase cycles
• fast read/slow write and erase
• generally limited to 32MB capacity
• more expensive/byte than NAND
•BIOS and firmware