Understanding RAM, SD Card and Device Memory of an smartphone

I have an Android smartphone and would like to understand what is the difference between RAM, SD Card and Device Memory.
When I check Memory Usage of my smartphone, I see those components:

RAM: 174 used      and   52 MB free

On SD Card: 492 MB used     and   3.16GB free

Device Memory: 143 MB used   and   47 MB free

I understand that "SD Card" is some external memory that you put in the Smartphone.  But how do I understand RAM and Device Memory?
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Joshua GrantomSenior Systems AdministratorCommented:
RAM is memory that is used by open applications, system processes, and the operating system itself. Any app you open uses ram to run.

Device Memory is the storage that is built into the phone. If you didnt have an SD card then any photos or music that you download would go on device memory.
Shahnawaz AhmedCloud Migration EngineerCommented:
Dear Miyahira

RAM is used by running processes on an as-needed basis. The biggest thing for SDK apps to note is that there is an upper bound as to how much RAM a process can consume

Device Memory is perceived to be the flash that is used to store APKs, ROM images, etc.

RAM stand 4Random Access Memory. It is d memory ur fone needs to run applications smoothly. Every file or app u open take up certain space 4rm ur RAM. Were d whole Ram is exhausted u wil have to close sum running apps to allow d running of another. Basically a fone of 1GB RAM wil allow d runnin of more apps at d same time dan a fone wit 515MB RAM while ur internal memory is d fone memory were u store ur music, videos, games etc, d internal memory can be expanded using memory card of ur choice size.
Hop dis helps
miyahiraAuthor Commented:
I do appreciate your help, but please, write in correct English. It's very hard to understand your last paragraph.
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Shahnawaz AhmedCloud Migration EngineerCommented:
Correction my last comment's last Paragraph.

RAM stand for Random Access Memory. It is the memory your phone needs to run applications smoothly. Every file or app you open take up certain space from your RAM. Were the whole Ram is exhausted you wil have to close sum running apps to allow the running of another. Basically a phone of 1GB RAM will allow the running of more apps at the same time then a phone with 515MB RAM while your internal memory is thr fone memory were u store your music, videos, games etc, The internal memory can be expanded using memory card of your choice size.
Hope this Help
Joshua GrantomSenior Systems AdministratorCommented:
device memory cannot be expanded. It is a fixed flash device. The SD card extends memory by adding an additional mounted disk.

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Shahnawaz AhmedCloud Migration EngineerCommented:
@Joshua > You right Device memory can not expand however If you have 8 GB Device memory + 8 GB SD that make usable memory Total = 16 GB , Out of 16 GB apx. 4 GB occupied by OS & Flesh
Joshua GrantomSenior Systems AdministratorCommented:
Yea, completely aware of how that works. That wasn't the question asked in the original post. Over explaining an answer does not help them understand.
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