A solid-state drive (SSD) is a data storage device that uses solid-state memory to store persistent data with the intention of providing access in the same manner of a traditional block i/o hard disk drive. SSDs are distinguished from traditional hard disk drives (HDDs), which are electromechanical devices containing spinning disks and movable read/write heads. SSDs, in contrast, use microchips which retain data in non-volatile memory chips[1] and contain no moving parts.[1] Compared to electromechanical HDDs, SSDs are typically less susceptible to physical shock, silent, and have lower access time and latency. SSDs use the same interface as hard disk drives, thus easily replacing them in most applications.[2]

As of 2010, most SSDs use NAND-based flash memory, which retains memory even without power. SSDs using volatile random-access memory (RAM) also exist for situations which require even faster access, but do not necessarily need data persistence after power loss, or use external power or batteries to maintain the data after power is removed.[2]

Until a few years ago, it was difficult to investigate a viable technological alternative to the hard drive. Storage device per excellence, and also the drive in 2006 celebrated its half century of existence. In 2009, if the hard disk has become more than ever the storage solution providing the cost per gigabyte, as a result of which, SSD technology overtook and now is growing to the point to justify this comparison.

The DSS for Solid State Drive, refers to compounds disks, not magnetic platters, but flash memory chips. The data is written on flash memory chips which offers two immediate advantages over the hard drive, access time of much lower and, especially, lower power consumption with the promise (not always held) performance higher. Side of the coin, SSD technology is expensive and offers reduced storage space. While the first hard drive came to € 80 offers 1TB of storage, the SSD with 80 GB of storage can be traded 400 euros each!

We will see through this comparison, if the difference in price is justified as we seek to explain the differences in technology, to analyze the performance and trying to sort in which an offer becomes inefficient. All the big names in the memory are in fact being SSD from Corsair to OCZ through Kingston as Samsung and Intel are also developing similar solutions. All are not present in this comparison, the manufacturers will send their products to the press test is quite variable. SanDisk Corsair and thus are absent from this issue …

SSD technology in detail: the architecture of memory
During our first record on SSD drives, the future of hard disk happen by the DSS? We already have mentioned the advantages of this type of drive face to traditional hard drives. We therefore do not return it, preferring to plunge us further forward in the retail technology. Physical disk SSD is composed of three elements: a PCB, single plate of silicon memory chips soldered on the PCB, and a controller controlling the whole. On memory, SSD drives use memory type NAND flash non-volatile.

There are two types of memory chips with SLC and MLC technologies. The chip type SLC (Single Layer Chip), storing one bit per transistor and are advertised as able to collect a total of 100 000 cycles erase / write. Meanwhile, MLC chip (Multiple Layer Chip) have a shorter life, namely 10 000 cycles erase / write but as they are cheaper and offer a storage capacity doubled in size chip equivalent. In terms of performance, the SLC chips offer theoretically better rates than MLC chips.

In terms of memory chips themselves, each is structured according to relatively complex blocks, themselves divided into pages. For example, a memory chip with a capacity of 2 GB, the blocks are typically 128 KB for page 2 Kb each. Read the operating mode of the memory requires the total load of the page or pages of writing while in each block must be written in its entirety. This means that writing 16 KB of data memory the process will take as much time as he had to write 128 KB … A real problem in terms of performance.

It is possible to circumvent this limitation by implementing cache or directly at the controller (on die) or through an external chip. With this in mind, some DSSs include a fourth element in their anatomy: a DRAM chip to act as cache. Warning, this is not systematic.

SSD Drives: Importance
With the growing technology, SSD’s have taken an important place in today’s world as compared to old hard drives. On an SSD, memory chips store data in the form of electrons, but with time, their cells are no longer able to retain power and they become unusable. To prevent wear and tear occurs too quickly, especially in writing on the same cells always, manufacturers have imagined the wear leveling: when writing data, the disk controller ensures and distribute them on up cells. To do this, the controller means to know precisely the number of entries received by each memory block …. With this information, it may allocate the best data.

Meanwhile, in addition to wear leveling, SSD drives incorporate ECC control errors. Specifically, when writing data if the disk controller detects an error, it immediately marks the defective memory and blocks and writes the data to another location on the disc. Naturally, the penalty in performance is not trivial in this case.


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Mahesh ( MGIT- ECE 3rd year)

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