This thread exists only to inform people of the types of computer storage that have been and are used by computers to store data. If you notice that any of my information is wrong (or some is missing) feel free to suggest that I edit the thread to make it correct.

Personal PC storage:

The 5.25-inch Floppy-
the mother of all computer storage today, these massive plastic sheets stored little to no data on them (from today's standpoint). Using a magnetic method of reading and writing, these disks were widely used for many years. These disks were also portable allowing people to transfer data from computer to computer.

Hard Disk Drive (HDD)-
The mother of all modern PC storage. When HDDs became available, computer manufacturers began to sell computers with an internal HDD installed. As storage began to evolve, the HDD became more versatile, and is still used today. HDDs often are cheaper than other modern internal drives and generally have more capacity. These disks use magnets to read and write data, however, the platters used to store data can be corrupted by dust or a broken head (heads are used to read and write on the disks. When a head breaks, there will be loud scratching noises from the platters that it scratches, the scratches cause physical damage to the platters and permanently break the HDD as a whole unit) they will no longer function. Traditional HDDs also have shorter life spans, but are cheaper and you'll probably buy a new PC before your drive fails anyway.

5-inch Floppy-
physically smaller diskettes that could hold more data. became more popular than the original ones.

CD (compact disc)-
This revolutionary technology enabled mass storage and simple transportation. CDs are much smaller and were mainly used for music, but could be used to install programs and applications. CD-ROM was a variant of the regular CD which had slightly increased storage and was designed for use with PCs

3.5 Inch Floppy-
The most popular form of storage of all time. These little guys store only 1.44 MB of data, but were light, small, and easy to transport. These particular Floppies are the most popular and may have been the inspiration for the "save" icon in Microsoft Office and other applications. These diskettes are now fading away, hardly anyone really knows much about them anymore and almost no one uses them. USB 2.0 to 3.5 inch floppy readers became very popular when traditional internal drives were hard to find in brand-new PCs. (in my honest opinion, someone should create a new version of the floppy that holds more storage. even if to just remind us all of these wonderful disks)

DVD-
created to hold videos/movies but could also hold larger applications and other data.

ZIP -
Very rare legacy storage device that was pretty expensive in the day (USB readers for modern PCs are still expensive adn can exceed 150 USD). Larger storage than 3.5 inch Floppy, but again, ZIPs were much more expensive and therefore, say, 50 floppies was more cost effective than 10 or so ZIPs

DVD-R/CD-R -
allowed users to write their own data to disks and transport amongst PCs

CD-RW/DVD-RW -
these disks replaced the old CD-ROMS and DVDs. They could hold significantly more data, and could even be written to again if necessary

Compact Flash (CF)-
came out around the time of DVD-RWs and was primarily used in digital cameras, until the time of ExpressCards...

ExpressCard -
Could be used for expanding storage, though was mainly used as a method of expanding ports or capabilities that your laptop didn't have before. Especially useful for adding things such as wifi, USB ports, or CF readers to laptops.

USB Flash Drive (aka thumb drive, pen drive, etc) -
Another revolutionary step in data storage, using expanded versions of RAM chips configured to be non-volatile (doesn't lose data when powered off). The early models featured small amounts of storage, but later began to feature much more (USB Flash storage is actually quite reflective of computer RAM storage. around the time when 500MB RAM was good, approx 300MB usb drives could have been found, though expensive.). USB drives were the most likely reason that Floppy drives were dropped by manufacturers.

SD/MMC cards -
SD and MMC are different, but are relatively the same. MMC came before SD and didn't feature as much storage. SD features large amounts of storage. These technologies came around a few years apart, SD being an upgrade of MMC featured the same dimensions and could be read from the same readers (SD readers would have faster read/write than MMC designed readers, but the backwards compatibility was the draw here).

Mirco SD -
*upgrade* of SD, pretty much the same but physically smaller. microSD to SD converter SD cards were released so that people could use micro SD cards in SD card readers. MicroSD was primarily designed for digital cameras, but recently became popular for upgradable storage in Android smartphones and tablets.

SSD -
someone had a brilliant idea of putting a bunch of RAM chips in a hard drive casing. The result: super fast read/write, low power consumption, no noise, and very reliable. Last much longer than traditional HDDs, can be fixed if there's a corruption issue. Problem: really really expensive for viable storage. SSDs are best for gamers and video editors. Otherwise just get and HDD...

External Drives -
*takes internal drive* *puts it in custom case* *sauters some wires* *plugs into PC via USB* *gets power via DC converter* *can read and write* *patent and sell* *$$$$$$$$* Basically just an internal drive inside a portable case that connects via USB. Very useful for mass data transfer, super portable desktop, backups, regular internal drive stuff. Can be booted from like any other boot enabled USB drive.

SERVER STORAGE:
Tape drives-
magnetic storage on long tapes. IDK how it works actually.

HDD/SSD -
already stated above