3.4a - Storage Devices: Professor Messer

Hard disk drives (HDDs)

• Non-volatile magnetic storage - function by using rapidly rotating platters.

• Random-access - data can be retrieved from any part of the drive at any time.

• Contains moving parts - spinner plates and a moving actuator arm. These components limit access speed, and can also break.

• HDD arm: Responsible for moving back and forth to find data on the HDD.

• HDD actuator: Mechanism that positions the read/write head over the correct track on the disk to read or write data efficiently.

• HDD platter: Circular disks within the HDD, coated with magnetic material, where data is stored in concentric tracks.

• HDD spindle: The rotating shaft that holds the HDD platters in place and enables them to spin at high speeds, allowing the read/write head to access data.

• HDD head: Used to precisely locate, retrieve, and write data to spinning platters.

Spindle speeds

• HDD spindle speed regulates how much latency (delay) for retrieving data from the HDD.

5,400 rpm

• 5,400 rpm: Spindle speed that provides about 5.55ms rotational latency.

7,200 rpm

• 7,200 rpm: Spindle speed that provides about 4.16ms rotational latency.

10,000 rpm

• 10,000 rpm: Spindle speed that provides about 3ms rotational latency.

15,000 rpm

• 15,000 rpm: Spindle speed that provides about 2ms rotational latency.

Form factors

• HDD form factors: Different sizes for HDDs found in computer systems - vary between 3.5”, 2.5”, and M.2 size.

3.5 inch

• Form factor commonly found on larger desktop

2.5 inch

• Form factor commonly found on smaller laptops

M.2

• Newer form factor that can be found on both laptops and desktops.

Solid-state drives (SSDs)

• Non-volatile storage device that contains no moving parts and uses flash memory chips to store data.

• Benefits of SSDs:

  1. No moving parts: no risk of mechanical failure that can cause data read/write issues.

  2. Very fast performance: no latency from spinning drive delays.

Communications interfaces

• Communications interface: Used to access data from an SSD/storage device

Non-volatile memory express (NVMe)

• Non-volatile memory express: Communication interface that is designed to match the throughput from an SSD - lower latency, and can use am M.2 form factor.

Peripheral Component Interconnect Express (PCIe)

• Peripheral Component Interconnect Express (PCIe): Expansion bus standard used to connect external devices to a motherboard (e.g., network cards, graphics cards, storage devices).

Serial Attached SCSI [Small Computer System Interface] (SAS)

Form factors

• SATA interfaces can be used with SSDs to improve data retrieval/performance.

M.2

• Smaller form factor that doesn’t require SATA data or power cables - pulls power directly from the motherboard.

• Can use a PCIe bus connection

  • 4 GB/s throughput or faster when using NVMe PCIe x4.

Mini-serial Advanced Technology Attachment (mSATA)

• Use of SSDs allows a decrease in the size of SATA drives - no spinning disk equipment.

• Size typically less than <2 inches.

Removable storage

Flash drives

• External storage devices that use EEPROM (Electrically erasable programmable read-only memory).

• Non-volatile and no power is required to maintain the data.

• Limited quantity of writes to the flash drive - once this threshold is surpassed, data is read-only.

Optical drives

• Use laser technology to read and write data on discs such as CDs, DVDs, and Blu-rays.

• Data is stored in pits and lands on the optical disc surface.

• Relatively slow - used for media that you don’t intend to change (e.g., archives).

• Many different formats (CD-ROM, DVD-ROM, Blu-ray)