32-bit vs 64-bit
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    Vi vs Vim vs gVim vs Neovim
    WAL vs rollback journal
    gtag vs Tag Manager
    stubs vs mocks vs fakes


Updated: 2021-12-04

For Consumers or Enterprises

  • For consumers, most of new laptops have SSDs inside; some desktops still use HDDs but the market if obviously shrinking.
  • For enterprises, HDD is still relevant, though usage of SSD is increasing as the prices decrease.


  • HDD: a shrinking business, only 3 big players: Western Digital (largest market share), Seagate, Toshiba
  • Flash Memory: Micron, Intel, Samsung, SK hynix, Kioxia

(Kioxia: spun off from Toshiba, kioku: a Japanese work meaning memory, axia: a Greek word meaning value)


HDD comes with one set of spinning platters. The platters gain capacity every year, but the drive spins at the same speed and the arm moves at the same speed, so a small read takes the same amount of time, typically several ms.

Typical SSDs will have a seek time between 0.08 and 0.16 ms. A solid state drive reads up to 10 times faster and writes up to 20 times faster than a hard disk drive.

"On a typical HDD, copying a large file, such as a movie or graphic design project, happens at a relatively pedestrian rate of 15 to 30 MB/s. A SATA SSD can copy the same file at 500 MB/s, while a newer NVMe SSD will reach speeds of 3,500 MB/s — that’s 3.5 GB per second."

By IOPS (Input/output operations per second): 100 iops for HDD, 10000+ for an SSD.


The highest-capacity 3.5 inch HDDs shipping commercially are 20 TB.

Backblaze (NASDAQ: BLZE publishes stats every quarter. Increasing: 14TB, 16TB decreasing: 4 to 12 TB.

Currently the largest portable hard drive (2.5 inch) you can buy is 5TB, and will likely stay at 5TB for a while.


  • both can use SATA
  • SSD also has NVMe, which is much faster.

Use Both SSD and HDD

Many databases and file systems can use either SSD or HDD as the underlying storage. HDDs have cheaper byte storage, while SSDs have cheaper IOs.

  • store data on SSD with failover to HDD. Need to closely monitor ssd usage, it may stop working or service will be degraded if ssd is full
  • use ssd as cache in front of HDD. Good for large datasets that cannot be placed entired on SSD: store all of the data in HDD but cache the hottest chunks in SSD,