While buying a new laptop, you might have seen people debating whether a device with an HDD is better or one with an SSD. What is HDD here? We all are aware of the hard disk drive. It is a mass storage device used generally in PCs, laptops. It stores the operating system and other application programs. An SSD or Solid-State drive is a newer alternative for the traditional Hard Disk Drive. It has come into the market much recently instead of the hard drive, which has been the primary mass storage device for several years.
Although their function is similar to that of a hard drive, they are not built like HDDs or work like them. These differences make SSDs unique and give the device some benefits over a hard disk. Let us know more about Solid-State Drives, their architecture, functioning, and much more.
What is a Solid-State Drive (SSD)?
We know that memory can be of two types – volatile and non-volatile. An SSD is a non-volatile storage device. This means that data stored on an SSD stays even after the power supply is stopped. Due to their architecture (they are made up of a flash controller and NAND flash memory chips), solid-state drives are also called flash drives or solid-state disks.
SSDs – A brief history
Hard disk drives were predominantly used as storage devices for many years. People still work on devices with a hard disk. So, what pushed people to research an alternative mass storage device? How did SSDs come into being? Let us take a small peek into the history to know the motivation behind SSDs.
In the 1950s, there were 2 technologies in use similar to the way SSDs work, namely, magnetic core memory and card-capacitor read-only store. However, they soon faded into oblivion due to the availability of cheaper drum storage units.
Companies such as IBM used SSDs in their early supercomputers. However, SSDs were not used often because they were expensive. Later, in the 1970s, a device called Electrically Alterable ROM was made by General Instruments. This, too, did not last long. Due to durability issues, this device also did not gain popularity.
In the year 1978, the first SSD was used in oil companies to acquire seismic data. In 1979, the company StorageTek developed the first-ever RAM SSD.
RAM-based SSDs were in use for a long time. Although they were faster, they consumed more CPU resources and were quite expensive. In early 1995, flash-based SSDs were developed. Since the introduction of flash-based SSDs, certain industry applications that require an exceptional MTBF (mean time between failures) rate, replaced HDDs with SSDs. Solid-state drives are capable of withstanding extreme shock, vibration, temperature change. Thus they can support reasonable MTBF rates.
How do Solid State Drives work?
SSDs are built by stacking together interconnected memory chips in a grid. The chips are made of silicon. The number of chips in the stack is changed to achieve different densities. Then, they are fitted with floating gate transistors to hold a charge. Therefore, stored data is retained in SSDs even when they are disconnected from the power source.
Any SSD can have one of the three memory types – single-level, multi-level or triple-level cells.
1. Single level cells are the fastest and most durable of all cells. Thus, they are the most expensive too. These are built to hold one bit of data at any given time.
2. Multi-level cells can hold two bits of data. For a givens space, they can hold more data than single-level cells. However, they have a disadvantage – their write speed is slow.
3. Triple-level cells are the cheapest of the lot. They are less durable. These cells can hold 3 bits of data in one cell. They write speed is the slowest.
Why is an SSD used?
Hard Disk Drives have been the default storage device for systems, for quite a long time. Thus, if companies are shifting to SSDs, there is perhaps a good reason. Let us now see why some companies prefer SSDs for their products.
In a traditional HDD, you have motors to spin the platter, and the R/W head moves. In an SSD, storage is taken care of by flash memory chips. Thus, there are no moving parts. This enhances the durability of the device.
In laptops with hard drives, the storage device will consume more power to spin the platter. Since SSDs are devoid of moving parts, laptops with SSDs consume relatively lesser energy. While companies are working to build hybrid HDDs which consume lesser power while spinning, these hybrid devices will probably consume more power than a solid-state drive.
Well, it looks like not having any moving parts comes with plenty of benefits. Again, not having spinning platters or moving R/W heads implies that data can be read from the drive almost instantly. With SSDs, the latency decreases considerably. Thus, systems with SSDs can operate faster.
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HDDs need to be handled carefully. As they have moving parts, they are sensitive and fragile. Sometimes, even a small vibration from a drop can damage the HDD. But SSDs have the upper hand here. They can withstand impact better than HDDs. However, since they have a finite number of write cycles, they have a fixed lifespan. They become unusable once the write cycles are exhausted.
Types of SSDs
Some of the features of SSDs are influenced by their type. In this section, we shall discuss the various types of SSDs.
1. 2.5” – Compared to all the SSDs on the list, this is the slowest. But it is still faster than HDD. This type is available at the best price per GB. It is the most common type of SSD in use today.
2. mSATA – m stands for mini. mSATA SSDs are faster than 2.5” ones. They are preferred in devices (such as laptops and notebooks) where space is not a luxury. They have a small form factor. While the circuit board in 2.5” is enclosed, the ones in mSATA SSDs are bare. Their connection type also differs.
3. SATA III – This has a connection that is both SSD and HDD compliant. This became popular when people first started transitioning to SSD from HDD. It is slow speed of 550 MBps. The drive is connected to the motherboard using a cord called the SATA cable so that it can be a bit cluttered.
4. PCIe –PCIe stands for Peripheral Component Interconnect Express. This is the name given to the slot that usually houses graphic cards, sounds cards, and the like. PCIe SSDs use this slot. They are the fastest of all and naturally, the most expensive too. They can reach speeds that are almost four times higher than that of a SATA drive.
5. M.2 – Like mSATA drives, they have a bare circuit board. M.2 drives are physically the smallest of all SSD types. These lie smoothly against the motherboard. They have a tiny connector pin and take up very little space. Due to their small size, they can quickly become hot, especially when the speed is high. Thus, they come with a built-in heatsink/heat spreader. M.2 SSDs are available in both SATA and PCIe types. Therefore, M.2 drives can be of varying sizes and speeds. While mSATA and 2.5” drives cannot support NVMe (which we will see next), M.2 drives can.
6. NVMe – NVMe stands for Non-Volatile Memory express. The phrase refers to the interface through with SSDs such as PCI Express and M.2 exchange data with the host. With an NVMe interface, one can achieve high speeds.
Can SSDs be used for all PCs?
If SSDs have so much to offer, why have they not fully replaced HDDs as the main storage device? A significant deterrent to this is the cost. Although the price of SSD is now lesser than what it was, when it made an entry into the market, HDDs are still the cheaper option. Compared to the price of a hard drive, an SSD can cost almost thrice or four times higher. Also, as you increase the capacity of the drive, the price quickly shoots up. Therefore, it has not yet become a financially viable option for all systems.
Another reason why SSDs have not fully replaced HDDs is capacity. A typical system with an SSD can have power in the range of 512GB to 1TB. However, we already have HDD systems with several terabytes of storage. Therefore, for people who are looking at large capacities, HDDs are still their go-to option.
We have seen the history behind the development of SSD, how an SSD is built, the benefits it provides, and why it has not been used on all PCs/laptops yet. However, every innovation in technology comes with its set of drawbacks. What are the disadvantages of a solid-state drive?
1. Write speed – Due to the absence of moving parts, an SSD can access data instantly. However, only latency is low. When data has to be written on the disk, previous data needs to be erased first. Thus, write operations are slow on an SSD. The speed difference may not be visible to the average user. But it is quite a disadvantage when you want to transfer huge amounts of data.
2. Data loss and recovery –Data deleted on solid-state drives is lost permanently. Since there is no backed-up copy of data, this is a huge disadvantage. Permanent loss of sensitive data can be a dangerous thing. Thus, the fact that one cannot recover data lost from an SSD is another limitation here.
3. Cost – This could be a temporary limitation. Since SSDs are a relatively newer technology, it is only natural that they are expensive than traditional HDDs. We have seen that the prices have been reducing. Maybe in a couple of years, the cost will not be a deterrent for people to shift to SSDs.
4. Lifespan – We now know that data is written to the disk by erasing previous data. Every SSD has a set number of write/erase cycles. Thus, as you near the write/erase cycle limit, the SSD’s performance may be affected. An average SSD comes with about 1,00,000 write/erase cycles. This finite number shortens the lifespan of an SSD.
5. Storage – Like cost, this can again be a temporary limitation. As of now, SSDs are available only in a small capacity. For SSDs of higher capacities, one must shell out a lot of money. Only time will tell whether we can have affordable SSDs with good capacity.