Applications Flash memory

1 applications

1.1 serial flash

1.1.1 firmware storage


1.2 flash memory replacement hard drives
1.3 flash memory ram
1.4 archival or long-term storage

applications
serial flash

serial flash: silicon storage tech sst25vf080b

serial flash small, low-power flash memory provides serial access data - rather addressing individual bytes, user reads or writes large contiguous groups of bytes in address space serially. serial peripheral interface bus (spi) typical protocol accessing device. when incorporated embedded system, serial flash requires fewer wires on pcb parallel flash memories, since transmits , receives data 1 bit @ time. may permit reduction in board space, power consumption, , total system cost.

there several reasons why serial device, fewer external pins parallel device, can reduce overall cost:

many asics pad-limited, meaning size of die constrained number of wire bond pads, rather complexity , number of gates used device logic. eliminating bond pads permits more compact integrated circuit, on smaller die; increases number of dies may fabricated on wafer, , reduces cost per die.
reducing number of external pins reduces assembly , packaging costs. serial device may packaged in smaller , simpler package parallel device.
smaller , lower pin-count packages occupy less pcb area.
lower pin-count devices simplify pcb routing.

there 2 major spi flash types. first type characterized small pages , 1 or more internal sram page buffers allowing complete page read buffer, partially modified, , written (for example, atmel at45 dataflash or micron technology page erase nor flash). second type has larger sectors. smallest sectors typically found in spi flash 4 kb, can large 64 kb. since spi flash lacks internal sram buffer, complete page must read out , modified before being written back, making slow manage. spi flash cheaper dataflash , therefore choice when application code shadowing.

the 2 types not exchangeable, since not have same pinout, , command sets incompatible.

firmware storage

with increasing speed of modern cpus, parallel flash devices slower memory bus of computer connected to. conversely, modern sram offers access times below 10 ns, while ddr2 sdram offers access times below 20 ns. because of this, desirable shadow code stored in flash ram; is, code copied flash ram before execution, cpu may access @ full speed. device firmware may stored in serial flash device, , copied sdram or sram when device powered-up. using external serial flash device rather on-chip flash removes need significant process compromise (a process high-speed logic not flash , vice versa). once decided read firmware in 1 big block common add compression allow smaller flash chip used. typical applications serial flash include storing firmware hard drives, ethernet controllers, dsl modems, wireless network devices, etc.

flash memory replacement hard drives

one more recent application flash memory replacement hard disks. flash memory not have mechanical limitations , latencies of hard drives, solid-state drive (ssd) attractive when considering speed, noise, power consumption, , reliability. flash drives gaining traction mobile device secondary storage devices; used substitutes hard drives in high-performance desktop computers , servers raid , san architectures.

there remain aspects of flash-based ssds make them unattractive. cost per gigabyte of flash memory remains higher of hard disks. flash memory has finite number of p/e cycles, seems under control since warranties on flash-based ssds approaching of current hard drives. in addition, deleted files on ssds can remain indefinite period of time before being overwritten fresh data; erasure or shred techniques or software work on magnetic hard disk drives have no effect on ssds, compromising security , forensic examination.

for relational databases or other systems require acid transactions, modest amount of flash storage can offer vast speedups on arrays of disk drives.

in june 2006, samsung electronics released first flash-memory based pcs, q1-ssd , q30-ssd, both of used 32 gb ssds, , @ least available in south korea.

a solid-state drive offered option first macbook air introduced in 2008, , 2010 onwards, models shipped ssd. starting in late 2011, part of intel s ultrabook initiative, increasing number of ultra-thin laptops being shipped ssds standard.

there hybrid techniques such hybrid drive , readyboost attempt combine advantages of both technologies, using flash high-speed non-volatile cache files on disk referenced, modified, such application , operating system executable files.

flash memory ram

as of 2012, there attempts use flash memory main computer memory, dram.

archival or long-term storage

it unclear how long flash memory persist under archival conditions – i.e., benign temperature , humidity infrequent access or without prophylactic rewrite. anecdotal evidence suggests technology reasonably robust on scale of years. datasheets of atmel s flash-based atmega microcontrollers typically promise retention times of 20 years @ 85 °c , 100 years @ 25 °c.

an article cmu in 2015 writes today s flash devices, not require flash refresh, have typical retention age of 1 year @ room temperature. , temperature can lower retention time exponentially. phenomenon can modeled arrhenius law.