Flash MemoryBY:IOSIF GRIGORYEVTONY BALLISTER

Agenda

Review SRAM/DRAM Review Flash memory NOR vs NAND logic Interesting facts HDD vs SDD

SRAM/DRAM

SRAM/DRAM rely on transistors to store data

SRAM Uses 6 transistors per bit

High energy, faster, more space consuming

DRAM Uses 1 transistor and 1 capacitor per bit

Lower energy, conventionally slower, smaller

Transistor

Typical: Source, Drain, Gate, Body Threshold voltage across gate Issue: Single Gate Cannot retain long-term information

Floating gates

Dual gates are conductive Insulating layers in between

Capacitor

Why doesn’t the capacitor discharge?

Deteriorates slowly 10 year decay

New Configuration

New long-term storage Typical configuration is obsolete

New NAND/NOR configurations

NOR Parallel connection of transistors

NAND Series connection of transistors

NOR vs NAND

NOR Better reading

Parallel configuration makes it larger

Focus: Code Execution

Typically used for ROM/BIOS

Uses random-access

NAND Better writing

Series configuration requires less space

Focus: Data storage

Typically used for flash drives/SSD

Uses page access

Writing Process

Write Must clear all data then write new data

Capacitors discharge then charge

Read Looks at pre-existing data

Buffer overflow

For flash: Regularly: writes to new block, and marks old ones dirty

When not in use: clears old blocks

Worst case: clears old blocks, then writes to them

For SSD: Regularly: Writes to a buffer inside the SSD

When not in use: clears buffer and writes to Flash memory

Worst case: buffer overflows, and slows writing from PC

Degradation

Floating gates require higher voltage Charge comes from substrate Diffusing charge causes oxide to degrade Balance between small oxide, and durability

HDD vs SSD

Magnetic Tape Reads and writes at similar speeds

Generally slower

Large and bulky

Very large capacity

Cheaper per Gbyte

Can easily fail

Flash Memory Reads fast writes slow, or very slow

Usually faster unless overflow

Can be very tiny

Smaller capacity

Expensive per Gbyte

Very durable

The benefits of flash

Flash drives Fast external drives Convenient and easy to use EEPROM/BIOS SD cards for the pi and cameras

REFERENCES! (…plz don’t sue us…)

SRAM pic: http://electronics.stackexchange.com/questions/30221/sram-and-flip-flops

DRAM pic: http://www.emrl.de/r_m_3.html

Transistor (Before): https://online.ece.nus.edu.sg/cnng/research.html

Transistor (After): http://www.eeherald.com/section/design-guide/esmod16.html

New Config: http://www.iue.tuwien.ac.at/phd/windbacher/node14.html

Capacitor pic: http://lwn.net/Articles/250967/

Flash Memory information (NAND vs NOR chart): http://en.wikipedia.org/wiki/Flash_memory

Flash degradation: http://www.storage-switzerland.com/Articles/Entries/2012/3/6_Why_Flash_Wears_Out_and_How_to_Make_it_Last_Longer.html

Second floating gate pic: http://www.explainthatstuff.com/flashmemory.html