Summary
Highlights
Computer memory (RAM) is volatile, meaning data is lost when power is off. To retain data, non-volatile storage devices like hard drives, SSDs, flash drives, and optical drives are used.
Hard drives are magnetic, random-access storage with rapidly spinning platters. They contain moving parts like platters, spindle, actuator arm, and read/write heads. Spindle speeds (RPMs) affect performance; higher RPMs reduce latency. HDDs come in various sizes like 3.5-inch for desktops and 2.5-inch for laptops.
SSDs use non-volatile memory with no moving parts, offering significantly faster read/write speeds than HDDs, greatly improving system throughput. Early SSDs were limited by SATA connections, leading to the development of PCI Express-based connections.
To overcome SATA's 6 Gbps limitation, SSDs connect directly to the PCI Express bus (e.g., via adapter cards), achieving speeds up to 64 Gbps per lane. NVMe (Non-Volatile Memory Express) is a low-latency protocol designed for PCI Express, enabling faster communication, especially in devices like laptops through M.2 interfaces.
SAS is a serialized version of SCSI, improving throughput for spinning hard drives to around 22.5 Gbps, much faster than SATA. SAS drives have distinct data and power connectors, preventing accidental interchanging with SATA drives, and are ideal for large storage arrays needing high throughput.
As storage devices shrank, new interfaces emerged. mSATA (mini SATA) was a smaller stopgap for traditional SATA connections. M.2 became a popular, compact interface for SSDs, directly connecting to the system’s bus for PCI Express speeds without additional cables. M.2 drives use 'keys' (B key, M key, or both) to indicate supported connectivity and throughput.
Flash drives utilize EEPROM (Electrically Erasable Programmable Read-Only Memory), which is non-volatile but has a limited number of write cycles. They are convenient for portability but not recommended for long-term archival due to limited write capability, small capacity, and ease of loss. Other flash storage includes Compact Flash, SD cards (mini/micro), and xD-Picture cards.
Optical drives (CD-ROM, DVD-ROM, Blu-ray) store data as microscopic bumps read by lasers. While slower than HDDs or SSDs, they offer significant data storage in a compact form factor, making them suitable for archiving. External drives are often used to access older optical archives.