Not all solid-state storage is the same. So, let’s take a look at the difference between the solid state drives (SSDs) becoming more mainstream in modern computers and the embedded MultiMediaCard (eMMC) storage you’ll often see in inexpensive tablets and laptops.
USB Sticks and SD Cards Also 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 might 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 are pretty simple, since they’re generally designed to be as cheap as possible. They don’t have the sophisticated firmware or other advanced features you’d find in an SSD.
There are a number of different “speed classes” of SD cards—and the slow ones are very slow. While it might be possible to install your operating system on an SD card, it would be a pretty bad idea. They are considerably slower than even the slowest SSDs.
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 are considerably more NAND chips in an SSD and they tend to be faster, better-quality chips.
SSDs also contain a controller with firmware that provides more advanced features. For example, an SSD controller spreads read and write operations over all the memory chips in the SSD, so it’s not limited by the speed of an individual chip as much. The controller works almost like a RAID configuration—it uses multiple chips in parallel to speed things up. When you write to an SSD, the drive might actually be writing to twenty different NAND flash chips at once, whereas writing to an SD card with a single chip might take twenty times as long.
The SSD’s firmware also performs wear-leveling operations to ensure that 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.
An SSD is also typically connected to the computer using a SATA 3, mSATA, or SATA Express interface, which are much faster than the interfaces available to a common flash drive or SD card.
A MultiMediaCard (MMC) is similar to an SD card. The SD card standard was considered an improvement over MMC and largely supplanted it in new devices. These days, almost all devices will favor an SD card slot over an MMC slot. The embedded MMC (eMMC) specification, however, continued to be developed and worked on.
An eMMC drive isn’t a sophisticated internal drive with speeds and features on par with an SSD. Instead, it’s basically an MMC that’s embedded onto a device’s motherboard. Like SD cards, MMC cards and their interfaces are much slower than an SSD. It gives manufacturers 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, eMMC doesn’t have the firmware, multiple flash memory chips, high-quality hardware, and fast interface that makes an SSD so fast. Just as SD cards are much slower than internal SSDs, eMMC storage is much slower than a more sophisticated SSD.
You’ll often find eMMC used 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 SSD with its increased size, complexity, and price. However, when you’re buying a laptop or tablet, the limitations of eMMC become more apparent. As with SD cards, not all eMMC storage is created equal—some eMMC storage is slower than others. However, all eMMC storage will be slower than a proper SSD.
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.