What does Form in storage mean? And SSD and RPM in Type?

SSD= Solid State Drive
RPM= how fast a HDD spins.

Form of Storage in Computer means :
Primary and Secondary
Primary is CPU Storage and RAM
Secondary means like CD/DVD , Hard Drives ,etc
Tertiary Storage is like flash drive or external hard disk

SSD Is Solid State Drive Which is faster than Hard drives
While RPM is Revolutions Per Minutes , it shows how fast the hard drive spins i.e Read and Write Data (generally)

@AirForce101HD - I've unselected your (second) choice of answer (my previous one) as "Best solution". This is a choice for the OP or - possibly - a moderator to make, not ordinary users.

<Please do not play moderator. If you have a problem with a best answer then alert the moderators and we will deal with it>

Agree that form here refers physical size i thought form of storage ( did not see example), my bad .

I'm sorry I'm still new to the forums.

PCIe would apply to adapters, cards, or PCIe based flash SSD cards, key things to note are if they are tall or low profile height cards, as well as if they require an x1 x4 x8 or x16 slot (also pay attention to mechanical e.g. slot size as well as electrical e.g. signal requirements for card and slot). There are also PCIe Gen 2 and PCIe Gen 3 slots and cards.

Form for storage means form factor such as 2.5" (e.g. Small Form Factor [SFF]) or 3.5" both of which are the width. Notebook and laptop drives tend to be SFF and can range up to around 2TB (thick or high profile) with 3.5" drives available in the 6-8TB range today. Note above I mentioned thick or high-profile as there is another form factor attribute of drives and that is height. Some SFF drives are not as thin e.g. thin such as 7mm for going into thin notebooks and tablets while others can be in the 9mm range. Make sure when getting a SFF 2,5" drive for a notebook, tablet, laptop or other thin device that it will fit in the drive enclosure/slot as a 9mm tall/high drive wont fit in a 7mm opening. Likewise there are also some tall SFF drives such as some of the 2TB models which while 2.5" wide, wont fit height wise into a standard laptop or note book drive opening. E.g. Pay attention to height and width (2.5" or 3.5").

Btw, media devices such as CD/DVD are 5.25" which is what HDD and some really old SSDs were also sized at...

RPM = Revolutions Per Minute which is how fast the drive spins such as 5,400 RPM (5.4K RPM), 5.9K, 7.2K, 10K, 15K and has a bearing on the performance. However there is also more to performance today than just RPM given some of the buffering, software/firmware algorithms in a drive (See how many IOPs can a drive do, it depends ...

Something else about drives are the interfaces and be careful not to judge a drive by its appearance alone (e.g. interface type, RPM, form factor) as there are many other factors and attributes (besides price per capacity).

See some images and info here and here that also has some additional information of HDD (and SSD) types, form factors, interfaces and other attributes.

Will leave mSATA and PCIe internal for laptops for a different discussion...