Solid State Devices. By Henry A. Spang V and Ethan Peters

Transcription

1 Solid State Devices By Henry A. Spang V and Ethan Peters

2 Presentation Overview 1. History of storage devices 2. Modern storage devices 3. How SSDs work 4. Improvements of SSDs over alternatives 5. Limitations of SSDs 6. Applications of SSDs 7. Current State and Future of SSDs

3 Punch Cards Originally made to drive looms in the textile industry (1725) First use in data appeared in 1890 while being used in the US Census Appeared in computers in the 1950's Allowed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

4 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 Magnetic Drums

5 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 Hard Disks

6 Floppy Disks 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

7 CDs 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

8 Modern Storage Devices 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

9 How SSDs Work 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

10 How SSDs Work (cont'd) 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

11 How SSDs Work (DRAM Style) An alternative to Flash SSDs is DRAM based SSDs o o Instead of using transistors to store the data, a capacitor is either charged or discharged to represent the bits value 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

12 Comparison

13 SSD Comparison (cont'd)

14 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

15 Applications of SSD Drives 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

16 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 EMC's Fast Cache

17 Future of SSDs As transistor size decreases, more can be fit into the SSD and thus their capacity increases However, the increase in capacity also causes a decrease in performance as there is more data to access Lessened performance goes against the mantra of the SSD, thus it may not have a bright future However, optimizations may be able to counteract any negative effects of increased capacity

18 Questions?

19 References exhibitions.uni klu.ac.at/index.php?id= art 3.jpg mag.com/id/7590/ IBM'S 360 and Early 370 Systems. MIT Press lib/browse.cfm?elib= memoright, html of the punch card