What is an SSD/SDD: Hard Drive Explained

Solid State Drives (SSD) use flash memory technology to improve hard drive speed, performance, and durability. It is a non-mechanical storage device that uses floating gate transistors (FGRs) instead of mechanical components to read and write data. 

This article will explain what SSDs are, particularly the various interfaces and form factors. It will also discuss the difference between SSD and HDDs as well as why SSDs are faster and better in performance. In the process, the article will discuss the flash memory technology and wear leveling mechanism in SSDs for improved speed and longevity.

Brief History of SSDs

solid state drives

The earliest use of the SSD technology dates back to the 1950s when it was first used in supercomputers. It was only feasible to use for military and aerospace technologies because it was very expensive and had limited storage of 2MB to 20MB. 

It was only in the 1990s where SSDs became available to consumers. However, SSDs back then had lifespan issues that were only resolved in the late 2000s. 

The first integration of SSDs in laptops was through the Asus EEE PC 700 released in the third quarter of 2007 followed by the OLPC XO-1 a year later. The Asus EEE PC 700 had 2GB of SSD while the OLPC XO-1 had 1GB of SSD. 

SSD technology improved in the following decade, improving capacity and branching out into different form factors. It has now become mainstream in laptops and desktop computers, providing an alternative to the slower and outdated hard-disk drives (HDD). 


Improving Speed

HDDs are composed of mechanical parts such as the platters, actuator arm, and the motor. The platters compose the tracks which are then divided into sectors. The tracks and sectors are responsible for storing the data while the actuator is responsible for locating the data within the tracks and sectors. 

SSDs are non-mechanical storage devices. It uses the same NAND Flash Memory technology as flash drives. 

It is comparable with the memory chips in Random Access Memory (RAM). However, RAM is a volatile memory device that wipes the data from the device when the power supply is removed. SSDs use non-volatile memory chips which retain the data even when power is cut. 

The floating gate transistors (FGR) make SSDs unique from HDDs because it retains the electric charge within the memory cell to indicate stored data. Each transistor can hold a single bit of data of either 1 or 0, indicating stored data or space, respectively. 

Its non-mechanical nature accounts for its silent and energy-efficient operation. The immovable parts in SSDs also allow it to withstand movement better than HDDs, making them more durable. 

SSDs provide faster loading times for games and applications. It also improves boot speed by a significant margin. There is also a marked improvement in copying files. To illustrate, copying files from an HDD will only reach up to 150MB/s. Copying from an SDD can reach up to 500MB/s and can even go higher at 3500MB/s for NVMe SSDs. 

Low-end laptops still use HDDs, but mid-range to high-end laptops now use SSDs to answer the demand for faster throughputs.

SSD Interface and Form Factor

ssd form factor and interface

The SSD interfaces available today are SATA, M.2, and PCIe. The 2.5-inch SSDs can use a SATA interface and can be placed in the provided SATA tray. This allows people with older CPUs to upgrade from HDDs to SSDs relatively easily (assuming the SSD comes with a mounting bracket).

A U.2 SSD is another type of SSD that also has a 2.5-inch form factor. However, this SSD uses a PCIe connection protocol instead of SATA for improved read/write speeds. 

The M.2 SSD is significantly smaller than the 2.5-inch SSD. It can come through M.2 SATA or M.2 NVMe. The M.2 SATA uses SATA connection while M.2 NVMe uses a PCIe connection for significantly faster read/writes.

The last SSD form factor is the PCIe Add-in Card or PCIe AIC. This type of SSD works similarly to graphics cards and connects to the computer via the PCIe slot. 

The various interfaces for SSDs are important because the hard drive is usually the bottleneck of the computer. A more advanced interface can decrease the bottleneck, allowing the computer to use the other hardware components more effectively. 

The SATA interface is one of the oldest interfaces for computers and is primarily designed for storage devices. SATA 3.0 can accommodate read/write speeds of up to 600MB/s. 

The PCIe interface, however, provides faster read and write speeds of up to 2000MB/s. It also supports higher bandwidth and lower latency for a faster interface between the storage device, RAM, and CPU.

Flash Memory Technology

Flash data storage technology is responsible for reducing computer bottleneck caused by the hard disk. The NAND flash memory chip contains flash memory cells which are composed of grids. Each grid can store data from 256kb to 4MB. 

However, the main feature of the NAND flash memory is the instant-accessibility of the files contained within the flash cells. This allows faster boot-up and little to no delay in opening applications. 

NAND flash memory technology is best for computers that perform heavy workloads such as servers and business computers. It can also benefit gaming computers because of the increasing volume of data and resources, including maps, textures, and characters, needed to run the most recent games. 

The latest in NAND technology is Vertical NAND, or V-NAND. In V-NAND memory cells are stacked vertically which allows for greater memory capacity. They also have faster read/write speeds while consuming less power. As a result they also have a longer service life than their planar counterparts. 

Wear Leveling in SSDs

Due to the difference in hardware, HDDs and SSDs also differ in organizing data within memory cells. Updating data in SSDs is more complicated than in HDDs.

SSDs require copying an entire block of data to another block, erasing the data on the block, then updating or rewriting the data. As such, most SSDs compensate by having overprovision of storage (not indicated in the computer) to provide ample space for updating files without reducing usable storage. 

However, NAND flash memory cells can degrade over time as resistance builds in the FGR during every erase cycle. This makes the charge necessary to change the gate inconsistent, potentially leading to cell rot. This can damage the writing process of the SSD and can render it a read-only storage device. 

Newer SSDs also have cell management mechanisms through built-in processes such as garbage collection and TRIM. Garbage collection refers to the process of wiping data from a block when the SSD is at an idle state. TRIM, moreover, is an Advanced Technology Attachment (ATA) command that works with garbage collection to ensure freeing the blocks from pages left by deleted files. These mechanisms prevent memory blocks from wearing and ensure a longer lifespan. 

SSDs today have spare cells that are used for bad block management. These spare cells can replace any potential bad cells in the SSD. Modern SSDs also have wear-leveling mechanisms where-in the SSD controller ensures that the write operation involves all cells rather than writing only on a single cell. This effectively prevents cell death that can lead to bad blocks.

HDD-SSD Hybrid Setup

SSDs are not solely improvements from HDDs. SSDs and HDDs can coexist in a computer set-up, but their respective roles can differ.

Usually, people using a hybrid SSD-HDD setups use the HDD for storing “cold” data or data that is not used regularly. This can include multimedia files and documents. The SSD then handles the “hot” data or data used for real-time monitoring, multimedia editing, or quick-access files. 

The SSD can also house online and offline games to take advantage of the fast read speeds for faster boot-up and loading times in-game. To illustrate, booting up GTA V using an HDD takes up to two minutes while booting up using an SSD will only take 25 seconds. 

It’s important to note that as technology has improved, the cost to storage capacity ratio for SSDs has only reduced. Back when SSDs were becoming popular I bought a 64 GB Crucial drive for boot-up. Last year I purchased a 2 TB SSD for the same exact price as the 64 GB drive.

Final Thoughts

SSDs provide a substantial improvement in computer hardware in terms of reducing bottleneck on performance, especially for midrange to high-end computers. Despite the steeper price, SDDs in a computer setup will provide a noticeable improvement in the speed and performance of the computer. 

A hybrid setup of HDD and SSD can address the bottleneck while also providing the convenience of greater storage.

About the author

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David Marshall

David follows the latest computer hardware trends: CPUs, GPUs, RAM, SSDs/HDDs, Mobos, CPU Coolers, and more. While some people may enjoy building birdhouses or model planes on their weekends, David opts to build and customize gaming rigs.