SSD commonly use NAND flash non-volatile memory and DRAM volatile memory, and manufacturers are more likely to use NAND non-volatile memory as the components of their products. It is because non-volatile flash memory allows SSDs to keep the complete data when the power is suddenly been cut off.
SSDs which are based on volatile memory like DRAM have fast access, less than 0.01 milliseconds with the use of accelerate applications. Without the accelerate applications, the speed may be held back by the latency of disk drives. DRAM-based SSDs involve internal battery and backup disk systems to guarantee the data persistence. If power is suddenly gone with some reason, the battery will keep the SSDs running and the data will be copied from RAM to the backup disk system. Once the power is retrieved, data will be copied to the main hard disk and the SSDs will resume to normal operation.
Architecture
The (SSD) Architecture has 3 parts: interface controller, processor system and FRAM block. The Processor system control the total functioning of the SSD by synchronizing the flow of information exchanged between the FRAM block and the interface controller. Also, the interface controller service the standard interface for a link between the PC and the SSD, Moreover, FRAM block store the information that has been written.
Function
Some of the functions in SSD including error correction, bad block mapping, read and write caching, and so on, because SSD have a controller to combine the electronics that bridge the NAND memory components to the host computer. SSD typically uses a small amount of DRAM as a buffer, similar to the cache in HDD. A directory of block placement and wear leveling data is also kept in the cache while the drive is operating.
Owing to the lower cost compared to DRAM and the ability to retain the data without a constant power supply, SSD manufacturers use non-volatile NAND flash memory in the construction of their SSDs, which can ensure data persistence through sudden power outages, it also is the higher performing of SSD, which have a capacitor or some form of battery; it can maintain the data integrity. For example: the data in the cache can be flushed to the drive if power is dropped suddenly.
Although host interface is not specifically a component of the SSD, it also is a key point of the drive. The interface is generally one of the interfaces found in HDDs. They include: Serial ATA, Serial attached SCSI, PCI Express, Fiber Channel and USB.
Advantages and Disadvantages
Like other electronic products, SSD also has its own advantages and disadvantage. One main advantage of SSDs is the speed; SSD is faster than other hard drives, because there are no spin-up and no read/write head. These make SSD has low startup time, low read, write latency times and no noise. Lower power consumption is another feature of SSD, this helps reducing heat production. SSD has a small size and light weight comparing to traditional hard disk drive, therefore it is an ideal storage device for all light weight and mobile product. SSD is more robust than hard disk drive, it is tougher and more resistance to impact, vibration and extreme temperatures. SSD can keep constant and deterministic the whole storage when doing your work so they are relatively deterministic performance.
About the disadvantages, the most important problem is the production cost, SSD is still far more expensive than other hard drives, however the cost can be reduced in the future because of the growth of the SSD market. The secondly problem is the capacity is far lower than usual hard drives. SSDs also have weakness including abrupt power loss magnetic fields and electric charges comparing to other hard drives. SSDs are limited write cycles, they usually will wear out after 300,000 to 500,000 write cycles, and high endurance Flash drives usually has 1 to 5 million write cycles. Today’s drives can last up 20 years. As SSDs generally very large, they are slower than common hard drives for random writes.
Comparative Analysis of SSD and HDD
Compare with power consumption, hard drives consume larger power than solid-state drive. Most of the hard drive is used motor to spin the disk. And high performance in a hard drive requires faster rotational speeds and power. The solid-state drive offers an enormous advantage over hard drives in power efficiency.
About the performance, hard drive’s access time is very slower. But Flash has faster access time. Moreover, SSD drives support even faster continuance reading and writing speeds than the hard drives.
In addition, SSD drives weigh only about half of a hard drive. The weight of circuit board is very light. About the performance, HDDs require heavier components to support the operation.
Market Segments
Notebooks
1. Home users prefer notebooks to desktops because they can use their computer in everywhere. Thus, they can do their own work in every time.
2. Business User prefers the notebook portable, they can take it to present the project every time. Notebooks are weighing less and consume less power.
Web Servers
Another application area is for web servers. The SSD has excellent sequential read transfer performance and a web server’s job is to serve many small files very rapidly.
Etc.. Industry
Any industrial products that require tolerance to extreme environmental conditions
1. ATM’s
2. Parking machines
3. Ticket vending machines
4. Factory automated machines
5. Medical Equipment
Questions
Q. Do SSD have any development of space?
A. Yes, but not too large, because SSD have more expensive price than other hard disk. Unless SSD have a breakthrough which is about development, otherwise SSD can’t substitute other types of hard disk.
Q. How about the lifespan of SSDs?
A. The file systems or firmware designs can mitigate this problem by spreading writes over the entire device (so-called wear levelling), rather than rewriting files in place. This problem is being improved all the time with lifespans increasing. Today's drives can last up to 20 years with average usage.
Q. Which two types of cell inside SSD?
A. Lower priced drives usually use multi-level cell (MLC) flash memory, which is slower and less reliable than single-level cell (SLC) flash memory. This can be mitigated or even reversed by the internal design structure of the SSD, such as interleaving, changes to writing algorithms, and higher over-provisioning (more excess capacity) with which the wear-leveling algorithms can work.
Q. Which types of SSD do you know?
A. The first type uses flash memory, and the second type that uses RAM (Both SRAM and DRAM), also known as Random Access Memory.
Both of these drives are better than standard hard drives, but they work in different ways.
Reference
http://www.supertalent.com/tools/ssd.php
http://hi.baidu.com/yanyulou/blog/item/eae50d244a69da36c995594d.html
http://ecet.ecs.ru.acad.bg/cst/Docs/proceedings/Plenary/P-2.pdf
