From Novice To a Masterpiece.

Flash Memory

The most interesting phrase in Science that one uses to herald new discoveries is not EUREKA! but "That's Funny...." Isaac Asimov

Introduction

It is very interesting to learn about new technologies. But here, the case is slightly different. This technology is not new!!! Nevertheless, it is a wonderful thing in itself and definitely makes an interesting read. Add to it an author like me, then what more can you ask for?? Ecstasy, you say? Positive.

Since the magnetic storage media that was in vogue had its negative points viv-a-vis bulkiness and reduced access speed, there was a need to introduce better storage. Flash memories had their birth in 1988 as replacements for magnetic storage. Did they really 'kick off' or 'kick the bucket'? Did that really happen, or, was there a twist in the story? Read on...

Before venturing into the details, let me give you a very brief intro to some of the related topics. I promise to keep it brief.

ROM: Read Only Memory or ROM is otherwise called Non Volatile Memeory. This is due to the fact that data can only be read from it and cannot be written onto it. It is programmed once and a set of values are stored in it. Even after a power failure the hold the data without losing one bit of it.
PROM: Programmable Read Only Memory is a enhancement of the ROM. Here, there is a possibility of programming the ROM albeit once. Nonetheless, this provides greater help as we can design the chip for the required specs. It is basically a matrix sort of arrangement wherein the fuses are connected between a row wire( called the WORD line ) and a column wire (called a BIT line). According to the specs the required fuses are burnt by supplying a voltage to the particular fuse. Thus the links that are required are kept intact while the links that are not needed are burnt.
EPROM: Erasable Programmable Read Only Memory gives you the all needed advantage of reprogramming the ROM. But this comes at a price. It is very difficult to erase the memory and program it again. In order to erase the memory, a beam of UV ray is applied for a certain period of time. This beam is passed thru a UV window provided on top of the chip. Later the chip is programmed and used.
EEPROM: Electrically Erasable Programmable Read Only Memory is a decent guy for sure. The advantage is that electric pulses can be used to erase the memory and the process is fast. EEPROMs are replacing the EPROMs and are being extensively used to store FIRMWARE. Firmware is the software that first runs when the PC is switched on and which initialises all the other devices attached to the PC. The BIOS(Basic Input Output System) is the Firmware.

Now that we have a decent knowledge about the different types of ROMs we can proceed with the discussion, one sided of course. Ah, one thing, all the info provided above is not really necessary for the discussion. Well, at least, not all!!

Flash Memory

Flash Memories are solid state chips which are non volatile. Non volatile memory implies that they don't lose the info when the power is turned off. They operate at high speeds. Since the magnetic storage devices which we use to store data are also non volatile but operate at lesser speeds, designers began to think of ways to substitute them with flash memories. Flash memories are high density devices i.e. they have one transistor per memory cell; similar to RAMs but with slightly different organisation.

So the first flash memories were credit card sized devices called as flash memory PCMCIA ( Personal Computer Memory Card International Association ) cards designed for portable comps. These had sizes from 20MB to 80MB. But why do we still use magnetic disks for storage?? Why haven't FMs completely replaced magnetic disks?? Why... Hold it guys! The answer follows....

Despite boasting qualities like ruggednes, high density and low power consumption they were not able to totally eliminate their seniors because they proved very costly and still continue to do so. Also, there are certain limitations on its operations.

'Write' operations on FMs are limited to around 100,000 times, though the 'Read' operations are innumerable. Hence designers had to provide spare cells so that once the deadline is reached, the spare cells could be utilised. Also the Write operation is complex with the required voltages being around 10V. Moreover this operation needs a certain amount of time to be completed.The figure displays the way the different operations are performed. Interesting, isn't it?

I suppose the operations are described in the figure in a lucid manner. It shouldn't be a problem for you to understand the working. Flash Memory is fast and slow vis-a-vis EEPROM. EEPROM works on one cell(a modified transistor called as a floating gate) at a time while FM works on blocks of cells thus making it a trifle fast. On the flip side EEPROM need not be erased before writing anything onto it while this guy needs to be. This reduces the speed of Write operations making it a slow customer.

Members of the Family

DataFlash

These modules are manufactured in the form of PCMCIA cards. To be precise they are packaged as Type II PC cards with ATA interface making them highly compatible. Almost all Laptops and small electronic devices ship with Type II PC card sockets. However, they are not used in portable MP3 players or small cameras. Size does matter, you see!

SmartMedia

Barely thicker than a playing card, these are less than a millimetre thick and occupy an area of about 4 sq.cm. They are usually plugged into the mobile devices thru various adapters. They are also called as Solid State Floppy Disk Card(SSFDC). You know the reason for this sobriquet. Don't you?

CompactFlash

Covering the same area as SmartMedia but 3mm in thickness, these cards use an IDE interface and include control circuitry for the memory. Available in capacities of more than 16MB, they are a trifle costly w.r.t SmartMedia. The controller helps during adapter complexity problems.

Why ain't it catching the eye?

Certain problems related to Flash Memory are:

They are very expensive. You can probably fix the price at Rs.700 per MB without being beaten up!!
Write or Erase operations limited to 100,000 times.
No one has still got the solution for the above problems!!!

Future of Flash

Despite having the problems ( Well, no one's perfect in this world, right?) Flash Memory is here to stay. The point that makes me feel so gung-ho about this is that devices which use the Read operations more often than the Write will use this because of the speed of operation. The ruggedness of these devices (it is nothing but a chunk of designer Silicon, call it "The Rock", if you like) makes them ideal for portable devices which need to sustain the trauma of travel troubles. Companies are frantically working on improving this technology. So be ready to be a part of the action! Ta Ta.