How does a Solid-State Drive work | HDD vs SSD | thebytewise



To understand How SSD works and what is the differences between SSD and HDD. We need to first understand how a Hard Disk Drive works.

In 1956, IBM shipped the world's first Hard Disk Drive or HDD, in the RAMAC 305 system. The drive used 50 24-inch platters, and it could store 5 megabytes of data, and the size you may ask? It took more room than two refrigerators. And it costs $50,000(1956).

Thankfully, since then due to advancements in technology Hard drives have grown much smaller and also less expensive. But even with all these advanced protection, Storage devices that have moving parts like Hard Drives can still sometimes fail, taking all those important pictures of yours with it.

A Hard Drive stores data on a series of spinning magnetic disks called platters which are divided into billions of small areas that can be independently magnetized or de-magnetized. There is an actuator arm with a read/write head attached to it. This arm moves along the spinning disk and positions the read/write head over the correct area of the drive to read or write information.

Because the actuator arm has to align the head over an area of the constantly spinning disk to read or write data, there is a delay before data can be accessed. Also, the head may have to move to different positions to load all the required files to launch a single program which means that it may have to wait for the platter to spin to the correct position multiple times before launching a program or loading a file.

Due to this Hard Drives aren't the fastest type of storage device available.


How SSDs are different


Solid-State Drives are called that specifically because they don't rely on any moving parts or spinning disks to store data. Instead, data is saved to a pool of NAND flash. NAND flash is made up of a type of transistor called a floating gate transistor. Unlike the transistor type used in DRAM(Dynamic Random Access Memory) which have to refresh multiple times per second, NAND flash is designed to retain its charge even when it's not being powered. This makes NAND a type of non-volatile memory.

One of the advantages of this system is that unlike HDDs as SSDs don't have any moving parts, they can operate at speeds far above those of a typical HDD. Although NAND flash isn't even nearly as fast as the main memory(RAM). But it's way faster than typical Hard Drives with spinning disks. Also as there aren't any moving parts involved, SSDs are also very strong as compared to HDDs, if you accidentally drop a Hard Drive, in most cases its a game over for it, but an SSD can generally withstand a few accidental drops and still be okay, which unless you are hitting it with a sled hammer. That's why it is more suitable for portable devices like Laptops or Tablets, which are more prone to accidental drops.

One of the functional limitations of SDDs is that while they can read and write data to an empty drive, overwriting data is much slower. This is because the only way for an SSD to update an existing page (areas where data can be stored) is to copy the content of the entire block into memory, erase the block, and then write the content of the old block + the updated page. If the drive is full and there are no empty pages available, the SSD first has to scan for blocks that are marked for deletion but that haven’t been deleted yet (overwritten with NULL data), erase them, and then write the data to the now-erased page. But this happens only when the SSD gets full and that's why the performance of an SSD starts decreasing when it gets full.

But if you buy an SSD with higher capacity, the performance of the SSD will also increase, as to increase the size of the SSD, of course, the manufacturer has to add more NAND flash modules, and the high-speed controllers can access multiple NAND modules at once that means more the number of NAND flashes more will be the speed of the SSD this will also increase the longevity of the SSD since the data cells of the SSD won't be written over and over again as many times.


But one the question arises is why can't the manufacturer just add multiple NAND flashes of lower capacity then everything will be equally faster?


The answer is, they can but they won't this isn't just some way to make users buy more expensive drives, the problem with this approach is that adding more modules of less size will be expensive for the company. Because manufacturing drives with less storage with more NAND flash modules will be almost the same as the amount of work they have to do for manufacturing drives of higher capacity, although the final product will be better, it just doesn't offer good value of the resources used.

It can be explained as silicon is cheap, its basically sand, but the process of turning that into a final product is not cheap.

Though this doesn't mean low capacity drives will be terribly bad, you will still get very good performance when compared to a typical HDD, but having an SDD with a larger size will have a little faster performance.


But this isn't actually a no-compromise deal, with all these added benefits, SSDs are also much more expensive than HDDs, for example: With $100 you can either buy a super-fast 256GB SSD or a relatively much slower 2TB Hard Drive.


The speed of the SSD will also depend on the type of SSD and also the type of NAND flash used.


There are several connectors types that the SSD uses to interface with the computer including SATA, PCIe, M.2, mSATA, SATA Express. For a consumer, the most common options are SATA and M.2.

SATA connectors are suitable for old computers as it has the connector type that Hard Drives uses, including SATA power and SATA data lines. This is the best way to boost up the performance of older computers, but one thing to be noted is that SATA drives are capable of the maximum theoretical transfer rate of 600MB/s.

That means SATA based SSDs cannot utilize the speed and efficiency of newer controllers like NVMe (Non-Volatile Memory express), which has a theoretical transfer rate of 3GB/s. Till now we already have established faster means more expensive, and yes NVMe drives are more expensive than SATA drives but considering the speed benefits of almost 5 times as fast as a SATA type SSD the price is quite appropriate.

So, the type of SSD a consumer needs will vary from person to person and also the use-case.


Does this mean Hard Drives are useless?


As SSDs offer more performance that doesn't mean Hard Drives are useless, depending upon the use-case sometimes Hard Drives can offer great value for less price. For instance, most of the file servers that companies use, has high capacity Hard Drives, because their main objective is to store files rather than super-fast transfers, though SSDs can be used in file servers, this won't is the best value for your money.

Also as a normal user, if you want to store files with very high size you can add a secondary SSD along with you HDD, and install all the important software that you use daily in the SSD and keep your movies and stuff on the HDD this will, significantly decrease the load time of the programs and will also prove to be a better value for your money.





Other useful links:

https://en.wikipedia.org/wiki/Solid-state_drive

https://www.extremetech.com/extreme/210492-extremetech-explains-how-do-ssds-work

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