Introduction to Flash

Modern memory devices whether SD, MMC, USB pen drive or CF cards all use the same type of storage chip as each other called Flash memory; Solid State Disks (or SSDs) also use them. Flash memory gets its name from how the devices operate but just what is flash memory?

Flash memory chips are non volatile computer storage chips, non volatile meaning they do not lose the data they hold when their power source is severed. The memory your computer uses for RAM is similar but it does not retain the data it holds after the computer is powered down, this is volatile storage, you can read more about volatile storage here/link.

Flash memory was developed from EEPROM which is Electrically Erasable Programmable Read-Only Memory. The two main types of flash memory are names after NAND and NOR logic gates. Very basically a logic gate is a device which implements a Boolean function which at its most basic is a true of false return.

NAND and NOR

NOR chips are beyond the scope of this text due to the fact that portable memory devices primarily use NAND chips.

A NAND or NAND gate is a logic gate which is the mathematical foundation to which NAND chips derive their operation, it is referred to a Negated AND or NOT AND, you can read more here.

Two common types of nand chip used in storage devices are:

TSOP48

TSOP stands for Thin Small-Outline Packages are a surface mounted integrated circuits. There are many variants of the TSOP chip starting with the Type 1 TSOP28 to the Type 2 TSOP66, their evolution being typical in that size decreases whilst capacity and performance increases. TSOP48 is the most common type used with storage devices. The 48 simply refers to the number of pins (or leads) that they use (24 at each end of the chip), you can see an image of a TSOP48 chip here.

TSOPs physical size ranges from a width of 8.1mm to 10.16 to a body length of 11.8 to 22.22mm and they vary greatly for capacity and performance.

BGA

BGA stands for Ball Grid Array is another common type of surface mounted integrated circuit packaging. As with TSOP there are variants of the BGA chip which can have hundreds of pins or leads and as with TSOP their evolution has lead to greater capacity and performance but they differ slightly in their design with TSOP chips having their leave at either end of the chip whilst BGA chip leads are located on the underside on the chip.

Designs for BGA chips differ greatly, you can see images of different BGA chips here.

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