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The Difference Between SSD and HDD Explained

With the continued drop in the price of solid-state drive (SSD), it is becoming more and more affordable option to the majority of computer users who, until recently, never knew any primary storage medium other than the traditional hard drive (HDD).

SSD has earned a huge reputation over the years for being a viable alternative to the traditional, old-fashioned hard dive (HDD), delivering the same functionality of storing data and all of its related aspects, but with much faster I/O rates, solid performance and high efficiency.

This article is NOT intended to illustrate the advantages of solid state drives (SSD), but rather to manifest the major differences between them and HDDs, because many users still think an SSD is just another form/brand of HDD but with a much faster speed, and this is way far from reality, as both drives only share the same functionality and form factors (the outer looks) as well, otherwise the difference between the two is vast.

We believe that to gain a full understanding of solid state drives (SSDs), one must be knowledgeable of the current generation of platter based drives, and in our pursuit to enlighten our readers on this material before they make their way to the world of SSDs, we have written this article with valuable information and simplified explanation which is supposed to give you a good overview on this topic, then you can decide whether an SSD is suitable for you or not.

HDD and SSD Explained

The traditional spinning hard drive (HDD) is the basic nonvolatile storage on a computer. That is, it doesn’t “go away” like the data on the system memory when you turn the system off. Hard drives are essentially metal platters with a magnetic coating. That coating stores your , whether that data consists of weather reports from the last century, a high-definition copy of the Star Wars trilogy, or your digital music collection. A read/write head on an arm accesses the data while the platters are spinning in a hard drive enclosure.

An SSD does much the same job functionally (saving your data while the system is off, booting your system, etc.) as an HDD, but instead of a magnetic coating on top of platters, the data is stored on interconnected flash memory chips that retain the data even when there’s no power present. The chips can either be permanently installed on the system’s motherboard (like on some small laptops and ultrabooks), on a PCI/PCIe card (in some high-end workstations), or in a box that’s sized, shaped, and wired to slot in for a laptop or desktop’s hard drive (common on everything else). These flash memory chips differ from the flash memory in USB thumb drives in the type and speed of the memory. That’s the subject of a totally separate technical treatise, but suffice it to say that the flash memory in SSDs is faster and more reliable than the flash memory in USB thumb drives. SSDs are consequently more expensive than USB thumb drives for the same capacities.

Form Factor

Although there’s almost no difference between SSD and HDD in the form factor, we preferred to include this point here to enrich your knowledge with this matter so as to get a bigger picture on the main topic. An SSD comes in traditional HDD form factors such as 5.25-inch, 3.5-inch, 2.5-inch or 1.8-inch. The largest size, 5.25-inch, is not widely used, except for special-purpose appliances, such as backup devices. 1.8-inch SSDs are used in removable and ultramobile applications. 3.5-inch drives are mainly used in desktop PCs and enterprise systems. Portable applications, such as laptops utilize 2.5-inch drives. 3.5-inch and 2.5-inch are the most common HDD form factors, and the same holds true for SSDs, as they will fit into the same slots as the identical size HDDs.

Architecture & Internal Components

You’re probably familiar with USB memory sticks – SSD can be thought of as an oversized and more sophisticated version of the humble USB memory stick. Like a memory stick, there are no moving parts to an SSD. Rather, information is stored in microchips. Conversely, a hard disk drive uses a mechanical arm with a read/write head to move around and read information from the right location on a storage platter. This difference is what makes SSD so much faster.

A typical SSD uses what is called NAND-based flash memory. This is a non-volatile type of memory. What does non-volatile mean you ask? The simple answer is that you can turn off the disk and it won’t “forget” what was stored on it. This is of course an essential characteristic of any type of permanent memory. During the early days of SSD, rumors floated around saying stored data would wear off and be lost after only a few years. data Regardless, that rumor is certainly not true with today’s technology, as you can read and write to an SSD all day long and the data storage integrity will be maintained for well over 200 years. In other words, the data storage life of an SSD can outlive you!

An SSD does not have a mechanical arm to read and write , it instead relies on an embedded processor (or “brain”) called a controller to perform a bunch of operations related to reading and writing . The controller is a very important factor in determining the speed of the SSD. Decisions it makes related to how to store, retrieve, cache and clean up data can determine the overall speed of the drive. We won’t get into the nitty-gritty details for the various tasks it performs such as error correction, read and write caching, encryption, and garbage collection to name a few. Yet, suffice to say, good controller technology is often what separates an excellent SSD from a good one. An example of a fast controller today is the SandForce SATA 3.0 (6GB/s) SSD controller that supports burst speeds up to 550MB/s read and write speeds. The next gen SandForce 3700 family of controllers was announced in late 2013, and is quoted to reach a blistering 1,800MB/s read/write sequential speeds as well as 150K/80K random IOPS.

Below is an illustration that clarifies the most significant parts of SSD and HDD:


This is where SSDs shine. An SSD-equipped PC will boot in seconds, certainly under a minute. A hard drive requires time to speed up to operating specs, and will continue to be slower than an SSD during normal operation. A PC or Mac with an SSD boots faster, launches apps faster, and has higher overall performance. Witness the higher PCMark scores on laptops and desktops with SSD drives, plus the much higher scores and transfer times for external SSDs vs. HDDs. Whether it’s for fun, school, or business, the extra speed may be the difference between finishing on time or failing.

We are not going to dive into the details of the advantages of solid state drives over traditional hard drives, as we have already made a special article for this purpose here.

Final Word

Hard-disk drives don’t perform nearly as well as solid-state drives or even hybrid products do in most situations, however. Today’s fastest hard drives can read and write data at more than 200MB per second with sub-8ms access times, but those numbers are significantly worse than the speeds of even some of the most affordable solid-state drives (which I’ll cover in a bit). The faster the platter rotation speed, the faster the hard drive. For example, a 7200-rpm drive outperforms a 5400-rpm drive.

Hard-disk drives are best suited to users who need vast amounts of storage and aren’t as concerned about achieving peak system performance. If you’re an everyday PC user who sticks mostly to email, Web browsing, and basic document editing, a standard hard drive should suit you fine. Just don’t tinker around with someone else’s SSD-powered PC, because once you’ve gotten a taste of a solid-state drive’s blazing read/write speeds, it’s hard to go back to even the speediest of traditional hard drives. If you’ve decided to go for a hard drive, check the best hard drive list where you’ll find the top performers in the hard drive industry.

As for solid-state drives, they are best suited to savvy PC users who seek high performance. If you don’t mind managing multiple volumes and you have the budget, pairing a fast SSD with a high-capacity hard drive will result in the best of both worlds. The SSD can hold the OS and your most frequently used applications, while the hard drive can handle the bulk-storage duties. Managing multiple storage volumes can be a bit of a pain for casual PC users; if you know your way around a PC, however, combining a fast SSD and large hard-drive storage is a great, high-performance approach with minimal compromise.

Updated: August 23, 2014 — 1:25 pm
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