Volatile vs. Non-Volatile Memory
- System memory (RAM) is volatile, meaning all data is lost when power is turned off.
- To retain data without power, non-volatile storage devices are required, such as:
- Hard drives
- Solid state drives (SSDs)
- Flash drives
- Memory cards
- Optical drives (CD/DVD/Blu-ray)
Hard Drives (HDDs)
- Magnetic storage devices with spinning platters that store data.
- Use a random access method, allowing immediate data retrieval from any location.
- Internal components include:
- Platters: Spinning disks where data is magnetically stored.
- Spindle: Rotates platters at high speeds (RPM).
- Actuator arm: Moves the read/write head across platters to
access data.
- Mechanical components make HDDs prone to failure over time.
- Must remain dust-free to avoid damage.
Hard Drive Speeds (RPM)
- Platter rotation speed affects performance:
- 5,400 RPM: Slower, common in budget or mobile devices.
- 7,200 RPM: Standard for desktops.
- 10,000 RPM: High-performance drives.
- 15,000 RPM: Fastest, used in enterprise environments.
- Higher RPM reduces latency, improving read/write speeds.
- Data access depends on the platter spinning to position the read/write head.
Hard Drive Form Factors
- 3.5-inch drives: Common in desktops due to larger size and higher capacity.
- 2.5-inch drives: Used in laptops and mobile devices for space efficiency.
- Modern SSDs often use smaller form factors like M.2 (22mm width).
Solid State Drives (SSDs)
- Use non-volatile memory with no moving parts, making them faster and more durable
than HDDs.
- Significantly improve system performance due to higher throughput and lower
latency.
- Commonly replace HDDs in modern systems for speed and reliability.
- Internally, SSDs contain memory modules where data is stored electronically.
SSD Interfaces and Performance
- Traditional SSDs used SATA connections, limited to ~6 Gbps throughput (SATA
3).
- To maximize SSD speeds, newer interfaces connect directly to the PCI Express (PCIe)
bus:
- PCIe adapter cards: Plug SSDs directly into motherboard PCIe slots for
higher speeds (~64 Gbps per lane).
- M.2 interface: Compact form factor for laptops/desktops, supporting PCIe
speeds.
- NVMe (Non-Volatile Memory Express): Protocol designed for SSDs to reduce latency
and increase throughput via PCIe.
- NVMe over M.2 can achieve ~20 Gbps speeds, far exceeding SATA limitations.
SATA vs. NVMe vs. SAS
- SATA (Serial ATA):
- Uses AHCI (Advanced Host Controller Interface) protocol.
- Max throughput: 6 Gbps (SATA 3).
- Common for HDDs and older SSDs.
- NVMe (Non-Volatile Memory Express):
- Designed for SSDs to leverage PCIe speeds.
- Low latency, high throughput (~20 Gbps on M.2).
- SAS (Serial Attached SCSI):
- Serialized version of SCSI for enterprise storage.
- Max throughput: ~22.5 Gbps.
- Used in high-performance storage arrays with HDDs.
- Physically similar to SATA but with different connectors to prevent mismatches.
M.2 and mSATA Interfaces
- mSATA (mini-SATA):
- Smaller form factor for compact devices.
- Limited to SATA speeds (~6 Gbps).
- Largely replaced by M.2.
- M.2:
- Modern interface for SSDs, supporting both SATA and PCIe/NVMe.
- No cables required; plugs directly into motherboard.
- Uses keying to designate compatibility:
- B key: Supports SATA or PCIe x2.
- M key: Supports PCIe x4 (faster speeds).
- Some drives support both keys for broader compatibility.
Flash Storage
- Uses EEPROM (Electrically Erasable Programmable Read-Only Memory) for non-volatile
storage.
- Common types:
- USB flash drives: Portable, small, and widely used.
- CompactFlash (CF): Older, larger format for cameras.
- SD cards (Secure Digital): Used in cameras, phones, and tablets.
- Variants: miniSD, microSD.
- xD-Picture Card: Older format for digital cameras.
- Limitations:
- EEPROM has a finite number of write cycles.
- Not ideal for long-term archival storage.
- Small size makes them easy to lose.
Optical Drives
- Use laser technology to read/write data via microscopic bumps on discs.
- Common formats:
- CD-ROM: ~700 MB capacity.
- DVD-ROM: ~4.7 GB (single-layer), ~8.5 GB (dual-layer).
- Blu-ray: ~25 GB (single-layer), ~50 GB (dual-layer).
- Slower than HDDs/SSDs but useful for archival storage.
- Declining in use but still relevant for legacy data access.
- External optical drives can be connected via USB.