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Compared Solid State Drive (SSD) with hard disk drives (HDDs)

Advantages

• New State of The Art Technology Solid State Drive (SSD) can be 2-3X faster than Previous Disk Spinning Hard Drive (HDD)
• Faster startup – as no spin-up is required.
• Near random access – since there is no read/write head to move.
• Extremely low read and write latency times – SSDs seek times are orders of magnitude smaller than the best current hard disk drives.
• Faster boot and application launch time
• Lower power consumption and heat production – at least for small SSDs. High-end SSDs and SSDs larger than 64GB may have a much higher power consumption.
• No noise – Lack of moving parts makes the SSD completely silent, although high-end SSDs and large SSDs may include cooling fans.
• High mechanical reliability – Lack of moving parts almost eliminates the risk of mechanical failure.
• High level of ability to endure extreme shock, high altitude, vibration and temperatures – SSDs are tougher than traditional hard drives. These features are useful for laptops, mobile computers, and devices that operate in extreme conditions.
• Relatively deterministic performance – unlike hard disk drives, performance of SSDs is almost constant and deterministic across the entire storage. This is because seek time can be constant, so file fragmentation has less impact on performance than on physical drives.
• For low-capacity SSDs, lower weight and size – size and weight per unit storage are still better for traditional hard drives, and micro drives allow up to 20 GB storage in a Compact Flash 42.8×36.4×5 mm (1.7×1.4×.2 in) form factor. Up to 64GB, SSDs are lighter than hard drives for the same size.

Architecture and function

An SSD is commonly composed of either NAND flash non-volatile memory or DRAM volatile memory.

SSDs based on volatile memory such as DRAM are characterized by fast data access, less than 0.01 milliseconds (over 250 times faster than the fastest hard drives in 2004) and are used primarily to accelerate applications that would otherwise be held back by the latency of disk drives. DRAM-based SSDs typically incorporate internal battery and backup disk systems to ensure data persistence. If power is lost for whatever reason, the battery would keep the unit powered long enough to copy all data from random access memory (RAM) to the backup disk. Upon the restoration of power, data is copied back from backup disk to RAM and the SSD resumes normal operation.

However, most SSD manufacturers use nonvolatile flash memory to create more rugged and compact alternatives for the consumer market. These flash memory-based SSDs, also known as flash drives, do not require batteries, allowing makers to replicate standard disk drive form factors (1.8-inch, 2.5-inch, and 3.5-inch). In addition, non-volatility allows flash SSDs to retain memory even during sudden power outages, ensuring data retrievable. Though flash SSDs are significantly slower than DRAM, they still perform excellently when compared to traditional hard drives in regards to reads. Indeed, flash SSDs have no moving parts, eliminating seek time, latency and other electro-mechanical delays inherent in conventional disks. Solid state drives are especially useful on a computer that has already come with maximum amount of RAM. For example, some computer systems built on the x86-32 architecture can effectively be extended beyond the 4 GB limit by putting the paging file or swap file on an SSD. These SSDs do not provide as fast storage as main RAM because of the bandwidth bottleneck of the bus they connect to, but would still provide a performance increase over placing the swap file on a traditional hard disk drive.

DRAM based SSDs may also work like a buffer cache mechanism. Whenever data is written to memory, the corresponding block in memory is marked as dirty and all dirty blocks can be flushed to the actual hard drive based on the following two strategies:

1. Time (e.g. every 10 seconds, flush all dirty data),
2. Threshold (when the ratio of dirty data to SSD size exceeds some predetermined value, flush the dirty data).

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