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To: limtex who wrote (12477)	7/3/2000 4:03:08 PM
From: Allegoria	Respond to of 60323

Flash Memory: White-Hot, But Why? Fayad Abbasi Jun 23 2000 streetadvisor.com In the past several months, flash memory has become a pretty hot topic in the world of semiconductors. Device makers will do almost anything to get their hands on flash memory at the moment. As we’ve written before, an executive even demanded recently that all his employees turn over their PDAs so the flash could be taken out and used on the company’s production line. If that’s not desperation, we don’t know what is… So the recent shortage has given flash quite a bit of press, but most reports don’t explain how it works or why it’s so important. We’re going to change all that. Let’s start with the basic functions. Flash is a non-volatile memory device, which means that, unlike most memory (such as DRAM), it can hold its contents once its power has been tuned off. Flash memory is similar to Electronically Eraseable Programmable Read Only Memory, or EEPROM. EEPROM is used to store basic instructions for simple devices or startup instructions for more complex devices such as PCs. The information is stored on EEPROMs by “burning” or writing it byte by byte at a higher-than-normal voltage. Burning cannot be done quickly and is usually done on a special machine. Flash has two advantages over EEPROM. First, writing to the memory doesn’t require a higher voltage and can be done on the fly. Second, flash memory stores items in blocks, so writes can be done quickly. All types of memory are composed of a network of transistors called “logic gates.” These gates consist of inputs and outputs that operate on Boolean logic. All digital devices use electronically transmitted binary values (0s and 1s ) to operate, and these values are combined in the gates to produce an output value. Here are some basic Boolean operations: AND: if all inputs are 1, the output is 1; otherwise the output is 0. OR: if all inputs are 0, the output is 0; otherwise it is 1. NOT: the output is the opposite of the input. 0 à 1 and 1 à 0. NAND: if all inputs are 1, the output is 0; otherwise the output is 1. OH NO!!!! Not again! NOR: if all inputs are 0, the output is 1; otherwise the output is 0. Memory cells are composed of cross-coupled NAND or NOR gates called “flip flops.” Each flip flop holds 1 bit of data. There are 23 bits in a byte, 210 bits in a kilobyte, and 220 bits in a megabyte. So, millions of these flip-flops are required for each megabyte of memory. Aside from all the manufacturer-specific “bells and whistles,” there are two basic types of flash: NAND and NOR. These names have to do with the basic structure of the logic gates and the Boolean logic of the chip. Most standard types of flash are NOR, while newer ones use NAND logic. Flash memory gets its name from the way the chips are erased. The memory cells are organized in such a way that an entire section can be erased in one operation known as a flash. When a block of memory is erased, a process known as Fowler-Nordheim tunneling takes place. This is where electric current crosses over a dielectric material to disrupt the electrostatic field in each floating gate. Flash memory has several applications, but most of them revolve around the same premise. Many different electronic devices require instructions when they start or “boot up”. A non-volatile memory is needed to store these instructions. In the past, EEPROM was used to store this data, but the information could not be updated without removing the chip. Firmware updates were usually non-existent because the chip or device had to be mailed to the manufacturer. Nowadays, flash memory is used to store this data because it can be updated quickly by special software. The best example of this evolution of technology is PC BIOS. Flash memory allows for easy updates and bug fixes, and most peripheral devices such as video cards contain their own BIOS, which can be easily updated. The other common use of flash is what we will call “medium-term storage.” Data is not temporary so it must be stored, but at the same time, it’s not permanent so it must be changeable. Digital cameras store pictures, and MP3 players store songs using flash memory. Cell phones and PDAs also use flash to store information. SanDisk [SNDK] even has a flash memory device for PCs that emulates a hard drive. Intel [INTC], AMD [AMD], and other large memory producers all produce flash memory. However, there are very few pure players in the flash industry—Silicon Storage Technology [SSTI] and SanDisk are the two that specialize in devices containing flash memory. Until production capacity can meet the growing demand, flash producers will continue to hold the winning hand. Good luck, Eric