Flash Memory

Presented By…Amit ParekhAmrinBhagya KumarHarshAnkush GandhiAkash VermaAbhishek

What is Computer Memory?Computer data storage, often called storage or

memory, refers to computer components, devices, and recording media that retain digital data used for computing for some interval of time.

Computer data storage provides one of the core functions of the modern computer, that of information retention.

It is one of the fundamental components of all modern computers, and coupled with a central processing unit (CPU, a processor),implements the basic computer model used since the

1940s.

Types Of StoragePrimary storage, presently

known as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them.

Example..RAMSecondary storage, or storage

in popular usage, differs from primary storage in that it is not directly accessible by the CPU.

Example..Hard Disk, Flash Memory

Continue…Static Memory

A form of volatile memory similar to DRAM with the exception that it does not refresh on occasion.

Dynamic Memory

A form of volatile memory which also requires the stored information to be periodically re-read and re-written, or refreshed, otherwise it would vanish.

Volatile Memory Requires constant power to maintain the stored

information. Since primary storage is required to be very fast, it predominantly uses volatile memory.

Non- Volatile Memory Will retain the stored information even if it is not

constantly supplied with electric power. It is suitable for long-term storage of information.

What is Flash Memory ?Flash memory, sometimes called flash RAM, is a

type of semiconductor device that combines important features of both memory & storage. These features include high-speed access and retention of data in the absence of a power supply.

Flash memory gets its name because the microchip is organized so that a section of memory cells are erased in a single action or "flash."

Flash memory refers to a particular type of EEPROM, or Electronically Erasable Programmable Read Only Memory. It is a memory chip that maintains stored information without requiring a power source.

How Flash Memory Works? It has a grid of columns and rows

with a cell that has two transistors at each intersection.

The two transistors are separated from each other by a thin oxide layer. One of the transistors is known as a floating gate, and the other one is the control gate.

The floating gate's only link to the row, or wordline, is through the control gate. As long as this link is in place, the cell has a value of 1.

To change the value to 0 requires a curious process called Fowler-Nordheim tunneling.

Flash Memory: Tunneling and ErasingTunneling is used to alter the placement of electrons

in the floating gate. An electrical charge, usually 10 to 13 volts, is applied to the floating gate. The charge comes from the column, or bitline, enters the floating gate and drains to a ground.

This charge causes the floating-gate transistor to act like an electron gun. The excited electrons are pushed through and trapped on other side of the thin oxide layer, giving it a negative charge.

These negatively charged electrons act as a barrier between the control gate and the floating gate.

A special device called a cell sensor monitors the level of the charge passing through the floating gate.

Continue…If the flow through the gate is above the 50 percent

threshold, it has a value of 1. When the charge passing through drops below the 50-percent threshold, the value changes to 0. A blank EEPROM has all of the gates fully open, giving each cell a value of 1.

The electrons in the cells of a flash-memory chip can be returned to normal ("1") by the application of an electric field, a higher-voltage charge.

Flash memory uses in-circuit wiring to apply the electric field either to the entire chip or to predetermined sections known as blocks. This erases the targeted area of the chip, which can then be rewritten.

Memory works much faster than traditional EEPROMs because instead of erasing one byte at a time, it erases a block or the entire chip, and then rewrites it.

Removable Flash Memory CardsWhile your computer's BIOS

chip is the most common form of Flash memory, removable solid-state storage devices are also popular.

SmartMedia and CompactFlash cards are both well-known, especially as "electronic film" for digital cameras.

Other removable flash-memory products include Sony's Memory Stick, PCMCIA memory cards, and memory cards for video game systems.

Continue…There are a few reasons to use flash memory

instead of a hard disk:It has no moving parts, so it's noiseless. It allows faster access. It's smaller in size and lighter.

So why don't we just use flash memory for everything?

Because the cost per megabyte for a hard disk is drastically cheaper, and the capacity is substantially more.

Continue…As shown below, SmartMedia

cards are extremely simple. A plane electrode is connected to the flash-memory chip by bonding wires.

The flash-memory chip, plane electrode and bonding wires are embedded in a resin using a technique called over-molded thin package (OMTP).

This allows everything to be integrated into a single package without the need for soldering.

The OMTP module is glued to a base card to create the actual card.

Advantage Of Flash Memory

The advantages of flash memory as compared with HDDs are substantial.

Smaller in size Light weightLow power consumptionLonger life expectancyGreatly improved shock resistance.

Disadvantage…The main disadvantage at present is that the cost per

unit of storage capacity is still much higher than that for HDDs.

However, the gap is gradually narrowing.In contrast to RAM and like all types of EEPROMs, it

wears out after a certain number of write and erase cycles. This is due to the degradation of the insulating oxide layer around the microscopic cells that are used to store data. Fortunately, however, the number of cycles in most applications is sufficiently low that this situation is not frequently encountered.

Bad Blocks

ApplicationsFlash memory is very useful

in a variety of applications including:

Your computer BIOS Memory Cards Mp3 players Modems Video game cards Digital cellular phones Digital cameras

SanDisk offers backup solution using flash memory

There is nothing more painful than losing data on a laptop, especially when you’re traveling. All you have to do is experience one failed hard drive to know how much your files may mean to you.

SanDisk has now offered its solution to this problem. The company has introduced the SanDisk FlashBack Adapter. The adapter makes use of an SD flash memory card to backup data which uses an ExpressCard slot in a laptop.

Once the user sets up what files they want to backup, the adapter will continuously back up data.

The adapter will also give you access to individual file restores in case you accidentally delete a file.