Solid State Devices
By Henry A. Spang V and Ethan Peters
Presentation Overview
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History of storage devices
Modern storage devices
How SSDs work
Improvements of SSDs over alternatives
Limitations of SSDs
Applications of SSDs
Current State and Future of SSDs
Punch Cards
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Originally made to drive looms in the textile industry (1725)
First use in data appeared in 1890 while being used in the US Census
Appeared in computers in the 1950's
Allowed for both the input of data and instructions
Magnetic Drums
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Invented in 1932, used in the 1950's, 60's
Utilized a ferromagnetic layer to read/write data
Different magnetic properties yielded a 0 or 1
1 track per head
Hard Disks
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Introduced in 1956 in the IBM 305 as the IBM 350 Disk File
Utilized a series of rigid rotating platters and magnetic fields to store data
One head per platter as opposed to one head per track
Floppy Disks
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Introduced in 1967 by IBM as read‐only storage used to load microcode into IBM 370s
Memorex introduced a
read/write version in 1972 with a capacity of 175 KB
Utilized a magnetic disk, similar to a hard disk's, that could be rotated by the drive reading it and read through a slot in the plastic casing
CDs
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First appeared in 1980
Single spiral track across entire disc
Bumps on the track cause the reflection of a laser to miss a receptor causing a signal low, if there is no bump it is a signal high
Later derivations allowed for the CDs to be re‐written (1996). This was done by replacing the built in bumps and pits with a crystalline layer that could be melted and resolidified to change the bit
Modern Storage Devices
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Conventional hard drives have reduced severely in price per capacity, now averaging ~8 cents/GB
Bandwidth now presents a limiting factor for modern computing platforms
Limited by mechanical nature
since reading requires
spinning up a physical
disk
How SSDs Work
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A traditional transistor looks like this in cross section
• When a voltage is placed on the gate, electrons in the silicon substrate move, creating a channel for current to flow from source to drain, or from drain to source
How SSDs Work (cont'd)
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Flash based SSDs make use of flash transistors, which look like this in cross section
When a large potential is placed on the control gate, electrons "tunnel" to the floating gate and become trapped there, creating a semi‐permanent charge
How SSDs Work (DRAM Style)
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An alternative to Flash SSDs is DRAM based SSDs
o Instead of using transistors to store the data, a capacitor is either charged or discharged to represent the bits value
o This causes the device to become volatile so a battery, separate power source, or super capacitor is required to store data
o The power sources can be used to maintain data until power is restored or just long enough to write to stable memory
DRAM SSDs are for extremely high performance applications
Comparison
SSD Comparison (cont'd)
Limitations
Reliability
Solid State Devices experience a high failure rate
Solution: Error‐Correcting Code (adds parity data to input data so it can be checked for integrity)
Lifetime
The transistors used in SSDs fail after tens of thousands of writes (compared to conventional hard drives, which typically undergo much more use before failure)
Solution: Wear leveling (writes data to different transistors so as to avoid using up certain sets of transistors)
Cost
SSD storage averages ~93 cents/GB, compared to ~8 for conventional hard drives
Solution: Smaller transistors leads to more storage as manufacturing improves the cost/GB will improve
Applications of SSD Drives
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One of the main benefits of SSDs is their minimal access time
In storage centers data that is accessed continuously will benefit from faster drives
SSDs are also popular in the media industry as they allow for entire movies to be entered into a cache like state
EMC's Fast Cache
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Multiple tiers of storage are utilized to organize data by its access rate
The more the data is accessed the higher it is moved in the tier structure
Allows for much faster access of important data
Future of SSDs
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As transistor size decreases, more can be fit into the SSD and thus their capacity increases
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However, the increase in capacity also causes a decrease in performance as there is more data to access
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Lessened performance goes against the mantra of the SSD, thus it may not have a bright future
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However, optimizations may be able to counteract any negative effects of increased capacity
Questions?
References
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http://cs‐exhibitions.uni‐klu.ac.at/index.php?id=222
http://media.bestofmicro.com/M/N/101903/original/image003.png
http://media.bestofmicro.com/N/A/101926/original/image006.png
http://media.bestofmicro.com/M/R/101907/original/image013.png
http://media.bestofmicro.com/M/V/101911/original/image017.png
http://www.columbia.edu/cu/computinghistory/card2.jpg
http://upload.wikimedia.org/wikipedia/commons/d/d2/Pamiec_bebnowa_1.jpg
http://www.designboom.com/history/floppydisk/01.gif
http://upload.wikimedia.org/wikipedia/commons/e/ed/Compact_Disc.jpg
http://i.zdnet.com/blogs/doc‐071210‐art‐3.jpg
http://en.wikipedia.org/wiki/File:Square_array_of_mosfet_cells_read.png
http://www.computerworld.com/s/article/9224322/SSDs_have_a_bleak_future_researchers_say
http://www.linux‐mag.com/id/7590/
IBM'S 360 and Early 370 Systems. MIT Press.
http://corphist.computerhistory.org/corphist/view.php?s=select&cid=9&PHPSESSID=4f0975e2ef57f8eaf4d40e8cec6fbd6f
http://www.magneticdiskheritagecenter.org/100th/Progress/Porter/jimporter.htm
http://archive.computerhistory.org/resources/text/Oral_History/5.25_3.5_Floppy_Drive/5.25_and_3.5_Floppy_Panel.oral_history.2005.102657925.pdf
http://www.aes.org/e‐lib/browse.cfm?elib=2912
http://www.newegg.com/
http://www.tomshardware.com/reviews/ssd‐memoright,1926‐6.html
http://whatis.techtarget.com/reference/History‐of‐the‐punch‐card
http://computer.howstuffworks.com/ram1.htm
http://matthensley.files.wordpress.com/2010/08/fast_cache.jpg