eMMC vs. SSD: Not All Solid-State Storage is Equal

By Chris Hoffman on September 19th, 2014


Not all solid-state storage is as fast as an SSD. “eMMC” is the kind of flash storage you’ll find in cheap tablets and laptops. It’s slower and cheaper than a traditional SSD you’d find in more expensive computers.

eMMC storage has a lot in common with SD cards. It’s all flash memory, but — just as an SD card wouldn’t be as fast as a speedy solid-state drive — eMMC storage can’t compete with an SSD, either.

USB Sticks and SD Cards Contain Flash Memory, But…

Flash memory — typically NAND flash memory — is found in USB flash drives and all the different types of SD cards you’d buy. USB flash drives contain a flash memory chip on a printed circuit board (PCB) as well as a basic controller and a USB interface. SD cards contain a flash memory chip on a circuit board along with an SD controller. Both SD cards and flash drives aren’t very sophisticated. They don’t have the sophisticated firmware or other advanced features you’d find in an SSD. They’re generally designed to be as cheap as possible.

There are a number of different “speed classes” of SD cards — and the slow ones are very slow. You wouldn’t install your operating system on an SD card if possible, as this would be much slower than using a good SSD.


Solid-State Drives Are More Sophisticated

A solid-state drive isn’t just the same components you’d find crammed into a flash drive or SD card. They have the same type of NAND flash memory chips, sure — but there’s more NAND chips and they tend to be faster, better-quality chips. However, the solid-state drive also contains a controller with a firmware that contains more advanced features. For example, the SSD controller spreads read and write operations over all the memory chips in the solid-state drive, so it’s not limited by the speed of an individual chip as much. The controller is almost like a RAID configuration — it uses multiple chips in parallel to speed things up. When you write to a solid-state drive, the drive might actually be writing to twenty different NAND Flash chips at once, whereas writing to an SD card might take twenty times as long as the SD card might only contain a single chip.

The solid-state drive’s firmware also performs wear-leveling operations to ensure data you write to the drive is spread across the physical drive evenly to prevent the flash memory from wearing out. The controller presents the memory to the computer in a consistent order so the computer behaves normally, but the drive is shuffling things around in the background. SSDs also support advanced features like TRIM to speed things up. There’s no real need for an “SSD optimization” utility because the SSD’s firmware is automatically optimizing the drive, shuffling data around for better performance.

A solid-state drive is also typically connected to the computer over a SATA 3, mSATA, or SATA Express interface, which will be faster than the interfaces available to a common flash drive or SD card.


eMMC Explained

A MultiMediaCard — also known as MMC — is similar to an SD card. The SD card standard was considered an improvement over MMC, so few devices have built-in MMC slots today — you’ll mostly find SD card slots instead. eMMC isn’t just an older type of storage, however. While MMC fell by the wayside, the eMMC specification continued to be developed and worked on.

eMMC stands for embedded MultiMediaCard. In other words, an eMMC drive isn’t a sophisticated internal drive with speeds and features on par with the SSDs you’d find in typical desktops and laptop computers. Instead, it’s basically a MMC — like an SD card — embedded onto the device’s motherboard. Like SD cards, MMC cards and their interfaces are much slower than an SSD. It’s a way to provide cheap internal storage. The eMMC device also has a controller that makes the eMMC bootable so it can be used as a system drive inside cheap Android, Windows, and Chrome OS tablets and laptops. However, it doesn’t have the firmware, multiple flash memory chips, high-quality hardware, and fast interface that makes a solid-state drive so fast. Just as SD cards are much slower than internal SSDs, eMMC storage is much slower than a more sophisticated SSD.

eMMC is typically a type of storage found in portable electronic devices like cell phones and digital cameras. With a push toward super-cheap $99 tablets and $199 laptops that need solid-state storage and not mechanical drives, cheap tablets and laptops are also being built with eMMC drives. You’ll typically see whether a device comes with an eMMC drive in its specifications. If the device is super-cheap, it probably has an eMMC instead of an SSD.


eMMC Isn’t Bad, But It’s Not The Fastest

There’s nothing wrong with eMMC in theory. Your digital camera probably doesn’t need a full solid-state drive with its size, complexity, and price. Some cheap, minimal, solid-state storage in the form of eMMC works well. The same applies to many other portable electronic devices that just need cheap, low-power, solid-state storage.

However, when you’re buying a laptop or tablet, the limitations of eMMC are more apparent. As with SD cards, not all eMMC storage is equal — some eMMC storage is slower than others. However, all eMMC storage will typically be slower than a proper solid-state drive. Cheap eMMC storage — along with cheap other components — are enabling laptops and tablets with solid-state storage to be as cheap as they are. However, that eMMC-based solid-state storage just isn’t as fast or robust as a full solid-state drive.

When comparing performance, you’ll probably want to look up storage benchmarks for the eMMC-based device in question– some devices are faster than others. Advances in hardware and new eMMC standards are making eMMC faster. However, if you’re a serious laptop user, you probably don’t want to be stuck with eMMC-based storage underlying your Windows laptop, even if it would save you some money.

Image Credit: mitpatterson2010 on Flickr, Darron Birgenheier on Flickr and Andreas. on Flickr (combined), Zhou Tong on Flickr

Chris Hoffman is a technology writer and all-around computer geek. He's as at home using the Linux terminal as he is digging into the Windows registry. Connect with him on Google+.

  • Published 09/19/14
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