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Comparison with hard disk drives
A comparison (with benchmarks) of SSDs, Secure Digital High Capacity (SDHC) drives, and hard disk drives (HDDs) is given in the reference.[6]
The disassembled components of a hard disk drive (left) and of the PCB and components of a solid-state drive (right).
The disassembled components of a hard disk drive (left) and of the PCB and components of a solid-state drive (right).
[edit] Advantages
* Faster start-up – as no spin-up is required. (RAM & Flash)
* Typically fast random access for reading – as there is no read/write head to move. (RAM & Flash)
* Extremely low read latency times – as SSD seek-times are orders of magnitude lower than the best current hard disk drives.[7] (RAM) In applications where hard disk seeks are the limiting factor this results in faster boot and application launch times ( see Amdahl's law).[8] (RAM)
* Extremely fast write (RAM only)
* No noise: a lack of moving parts makes SSDs completely silent, unless, as in the case of some high-end and high-capacity models, they have cooling fans attached. (RAM & Flash)
* For low-capacity flash SSDs, low power consumption and heat production when in active use - although high-end SSDs and DRAM-based SSDs may have significantly higher power requirements. (Flash)
* High mechanical reliability – the lack of moving parts almost eliminates the risk of mechanical failure. (RAM & Flash)
o Ability to endure extreme shock, high altitude, vibration and extremes of temperature: once again because there are no moving parts.[9] This makes SSDs useful for laptops, mobile computers, and devices that operate in extreme conditions. (Flash)[8]
* Larger range of operating temperatures. Typical hard drives have an operating range of 5-55 degrees C. Most flash drives can operate at 70 degrees, and some industrial grade drives can operate over an even larger temperature range.[10]
* Relatively deterministic read performance:[11] unlike hard disk drives, performance of SSDs is almost constant and deterministic across the entire storage. This is because the seek time is almost constant and is not dependent on the physical location of the data, and so, file fragmentation has almost no impact on read performance.
* For low-capacity SSDs, lower weight and size: although size and weight per unit storage are still better for traditional hard drives, and microdrives allow up to 20 GB storage in a CompactFlash 42.8×36.4×5 mm (1.7×1.4×.2 in) form-factor. Up to 256 GB, SSDs are currently lighter than hard drives of the same capacity.[9]
[edit] Disadvantages
* Price – as of mid-2008, SSD prices are still considerably more costly per gigabyte than are comparable conventional hard drives: around USD 3.50 per GB[12] for flash drives and over USD 80 per GB for RAM-based compared to typically less than USD 0.26 (Retail) and as low as 0.14 for OEM models for mechanical drives.
* Capacity – although currently far lower than that of conventional hard drives, SSD capacity is predicted to increase rapidly, with experimental drives of up to 1 TB in test.[13][14]
* Higher vulnerability to certain types of effects, including abrupt power loss (especially DRAM based SSDs), magnetic fields and electric/static charges, in comparison to normal HDDs (which store the data inside a Faraday cage).
* Limited write cycles – flash-memory cells will often wear out after 10,000-100,000 write cycles[citation needed], while high endurance cells may have an endurance of 1–5 million write cycles (many log files, file allocation tables, and other commonly used parts of the file system exceed this over the lifetime of a computer.[15] Special 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.[16] Today's drives can last up to 20 years with average usage.[dubious – discuss] An example for the lifetime of SSD is explained in detail in this wiki.[dubious – discuss] SSDs based on DRAM, however, do not suffer from this problem.
* Slower write speeds – as erase blocks on flash-based SSDs generally are quite large, they are far slower than conventional disks for random writes and therefore vulnerable to write fragmentation,[17] and in some cases for sequential writes.[8] SSDs based on DRAM do not suffer from this problem.
* Lower storage density – hard disks can store more data per unit volume than DRAM or flash SSDs, except for very low capacity/small devices.
* Higher power consumption at idle or under low workloads laptop battery runtimes decrease when using an SSD over a 7200 RPM 2.5" laptop hard drive,[18] flash drives also take more power per gigabyte.
o RAM based SSD require more power than hard disks, both operating and when turned off.[19]
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