Hard Drive

Persistent storage, aka “non volatile” storage means that the data are stored, even when power is removed. A laptop might use a spinning hard drive or it could use a Solid State Disk (SSD) to store data.

Persistent storage stores the computer’s operating system, individual applications, and saved files. These applications are accessed from the drive and pulled to RAM when needed. Hard drive storage is slower, but cheaper, than RAM¹. A hard drive has a lot of storage (256GB to 1TB) compared to RAM (4 GB to 16 GB)

Persistent Storage: Hard Drive vs. Flash Storage (SSDs)

Hard Drives (HDDs):

Use spinning metal disks and magnetic patterns to store data.
Contain moving parts like platters and a read/write head.
Often make a high-pitched spinning or clicking sound.
Generally cheaper per byte and offer higher capacities.
Slower performance, higher power use, and more prone to damage.

Flash Storage (SSDs):

“Solid state”: no moving parts, just chips with electrons.
Solid-state drives (SSDs) use solid-state memory that emulates a hard disk drive interface to store data.
Found in USB drives, SD cards, phones, tablets, and modern laptops.
Faster, quieter, and more power-efficient than HDDs.
More durable and shock-resistant.
More expensive per byte, but prices have been dropping.
Much slower than RAM, so not a replacement for memory.

Arshane88 / CC BY-SA 4.0 / Wikimedia Commons

SSDs are drives made from certain types of flash memory (like a USB). There are a few different kinds; the image below shows NAND-based non-volatile memory.

If you have a newer laptop computer, you likely have an SSD, not a spinning hard drive.

Uses (Both HDDs and SSDs):

Store files, documents, apps, music, and more.
Keep applications and data when not in use.
For more details on differences between SSDs and HDDs, you can check the article here.

External Permanent Storage

Removable disks are alternatives to the internal hard drive for reading and storing data. External hard drives will work like the ones that are built-in. A USB flash drive is also a flash drive, much like an SSD (and yes, you can boot a computer up from a USB). For completeness, we’ll mention CD drives, even though they’re less commonplace nowadays.

Removable Storage

External Hard Drives.
CD/DVD/Blu-Ray Drives, though optical media are less common for data storage today.
USB flash drives. USB Type-C and Thunderbolt interfaces provide high-speed data transfer for external storage.
CD/DVD-ROM/RWs. Less common nowadays.

More Information:

How does a CD Drive Work?

A stamped CD (such as a purchased music CD) has a layer of plastic with bumps imprinted into it starting from the center and radiating outward around the disc. Over the layer of plastic is a layer of aluminum. This layer of aluminum makes the bumps and lands reflective so that a laser can bounce off the surface and return to an optical pickup. The optical pickup interprets the laser reflection as a bit and sends it to the computer for use. Acrylic is layered over the aluminum to protect it, and a label is placed on top.

A CD-R has a slightly different physical make up. It has a flat (no bumps) plastic layer, a layer of dye, a layer of aluminum, a layer of acrylic, and finally the label. The dye layer is darkened in the “burning” process. The laser then reads these darkened sections as bumps on the CD and interprets the information.

Exercises²

If you could build your own personal computer, what components would you purchase? Put together a list of the components you would use to create it, including a computer case, motherboard, CPU, hard disk, RAM, and DVD drive. How can you be sure they are all compatible with each other? How much would it cost? How does this compare to a similar computer purchased from a vendor such as Dell or HP?
What is the current status of solid-state drives vs. hard disks? Research online and compare prices, capacities, speed, and durability. If you write an essay, be sure to give attribution to your sources.