Technology:
It is a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory) .
It comes in NAND and NOR types. NOR-type has long erase and write times, but provides full address and data buses, allowing random access to any memory location. while NAND-type has faster erase and write times, and requires a smaller chip area per cell, (thus allowing greater storage densities and lower costs per bit than NOR flash). it also has up to ten times the endurance of NOR flash. However, the I/O interface of NAND flash does not provide a random-access external address bus.
NOR type flash is for faster read access (can be used where ROM is required), NAND type is used for storage (can replace hard drives, CD, DVD etc).
Advantages:
Unlike in hard drives theres no moving part in flash memory, so it requires less power, and more shock resistance. so flash is becoming more popular in portable devices.
less latencies compared to hard drive.
Limitations:
1. with flash memory is it has a finite number of erase-write cycles.
2. limited capacity compared to hard drives
but the number of cycles, capacity increases with technology improvements.
Transfer Rates:
Commonly advertised is the maximum read speed. it is represented in "x" format or MB/s
1x is equal to 150 kilobytes per second.
So a 100x memory card goes to 150 KB x 100 = 15000 KB per second = 14.65 MB per second.
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Rating Speed (MB/s)
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6x 0.9
32x 4.8
40x 6.0
66x 10.0
100x 15.0
133x 20.0
150x 22.5
200x 30.0
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Flash memory comes in different types, capacities, shapes and sizes.
different companies makes them in different varieties. below are list
of popular flash memory types.
- Compact flash from sandisk
- Memory Stick from sony/sandisk
- Secure digital (SD) from panasonic, toshiba, sandisk
- xD from olympus, fujifilm
- USB flash drives from various manufactures, and Universally compatible across all computer platforms using USB 1.1/2.0
Compact Flash
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Memory stick
1. standard (50 mm x 21.5 mm x 2.8 mm),
2. Duo(31 mm x 20 mm x 1.6 mm),
3. Pro Duo(31 mm x 20 mm x 1.6 mm)
4. Micro(15 mm x 12.5 mm x 1.2 mm)
1 2 3 4
  |  |  |  |
SD, mini SD, micro SD, SDHC
SDHC extension to SD, it has capacities exceeding 2GB
SDHC has speed class rating
class 2 - 2MB/s
class 4 - 4MB/s
class 6 - 6MB/s
xD (standard, type M, type H)
Thin and small (20 mm × 25 mm × 1.78 mm)
 |  |  |
USB (no standard size, comes in various sizes and capacities)
