Comparing the Speed of SSD, eMMC, Flash Drive and SD Card

Pawit Pornkitprasan
3 min readApr 6, 2021


Decently large flash storage such as 64 GB flash drives or SD cards are now very affordable. With such a large size, one might think, why not install Windows or Linux on it and use it instead of a hard drive? Not a live-CD-style installation but an actual installation.

I have tried it before and while it works, the speed is excruciatingly slow despite performance ratings such as 100 MB/s read speed. This is actually because while sequential performance (reading/writing large files) is good, random performance (reading/writing many small files like running an OS) is not so good.

There are SD card standards such as A1 or A2 which claims are for “application performance” and cards rated as such are supposed to have better random performance. Today, I’ve ran some benchmark to compare the speed of SSDs, flash drives, SD cards and eMMCs.

The test subjects are:

  • WD Green 120 GB SATA SSD (WDS120G2G0B) — An entry-level SATA SSD.
  • SanDisk 128 GB eMMC (DF4128) — The eMMC which comes embedded in my Acer Spin 1. It may be the iNAND 7232.
  • SanDisk Ultra Flair 64 GB Flash Drive (0781:5591) — A USB 3.0 flash drive from SanDisk
  • SanDisk Ultra A1 64 GB SD Card (SKU: SDSQUA4–064G-GN6MN, CSD: SD64G) — An “A1” SD card rated for “up to 120 MB/s” read
  • SanDisk Extreme A2 64 GB SD Card (SKU: SDSQXA2–064G-GN6MN, CSD: SN64G) — An “A2” SD card rathed for “up to 160 MB/s” read and “up to 60 MB/s” write

For SD card, we need card readers, so I’m testing with 2 separate readers:

  • Intel SDXC/MMC Controller (8086:5aca) — The built-in card reader of my Acer Spin 1. It comes built in to the Intel N4200 SOC and uses the PCI bus, so it should provide very good performance.
  • Alcor Micro Corp. Multi Flash Reader (058f:6366) — The built-in card reader of my HP laptop. It uses the USB 2.0 bus and thus is limited to USB 2.0 speed.

Now for the results:

For raw results, please see


  • For random writes, the SSD and eMMC are leagues ahead of flash drives and SD cards. This is probably also the reason many phone manufacturers are removing SD card slots — internal memory are just that much faster and slow SD cards make the phone unresponsive.
  • The SanDisk A2 SD card performs very similarly to the A1 SD card except for the sequential write speed. Thus, the A2 card is probably only worth it if you need faster sequential write.
  • Random writes on SanDisk A1/A2 are a lot better than the flash drive, so running OS off them should be more responsive, but still no where near SSDs and eMMCs.
  • Random reads performance are very similar between the different media. USB 2.0 also slows down random read even if it’s no where near the USB 2.0 speed limit (or maybe it’s the card reader)

Hope you have found this comparison useful!