ELI5: What exactly is Random Access Memory?

Submitted by FilmFrench t3_10oul8w in explainlikeimfive

When I look up what ram means, the description is that it's short term memory for the office and apps will restart if they don't have enough RAM. When I hear that story, I associate it with YouTube. I'll watch a YouTube video, then pause and go to Facebook and when I return to YouTube, the video is gone. Or maybe I'm scrolling through Amazon, reach the bottom of a page, go to another app and then return to Amazon and I'm at the top. This is pretty annoying and if more RAM would fix this problem, then I would certainly want more RAM on my phone, but the feedback that I'm getting is that this is not what ram is and if that is true, then I have no clue what ram means.

Can someone please explain?

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Fred2718 t1_j6isch7 wrote

random access memory was first named that to distinguish it from serial access memory, more familiarly called magnetic tape.

Imagine a library of 1000 books. Ram is like having all the books sorted and ready to easily grab on a big bookcase. All books take about the same short time for you to grab.

Serial access is like all the books are laid out in a long line on a conveyor belt. To get a particular one, you have to stand and wait until the conveyor brings it to you.I

I'll let others explain the modern differences among RAM, ROM, and SSD, and HDD.

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d4rkh0rs t1_j6iw1nd wrote

good answer, except your conveyer belt should have the pages laid out. and make you read to the part you need.

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Fred2718 t1_j6izhk0 wrote

Disagree. The tapes I used, in the 70s and early 80s, 9 track 6250 BPI in NRZI, used 4K up to 32 K byte records with inter-record gaps. Controllers could count records on the fly without moving data to ram, until you got to the record you wanted.

A lot like sectoring on HDD.

/Pedant_Mode_Off

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d4rkh0rs t1_j6jk32l wrote

I just missed the tape era(unless Sinclair and Commodore count).
My understanding was the original systems had to read each header without a good index allowing them to jump to record X.
It sounds like your systems were a bit more advanced.

I bow to your greater experiance while wishing we could hear from the 50s and 60s.

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Fred2718 t1_j6jpki5 wrote

Mainframe systems maintained tape record indices ( after reading them from tape) in RAM or "drum" disk for just this reason. Read Knuth on efficient tape database searches, if you have a kink for antique software engineering. But bear in mind I was working on IBM 360 and 370 mainframes, followed by Data General minicomputers in the 80s.

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maveric_gamer t1_j6j6o9r wrote

RAM is where your computer stores either the active program(s) it's running, or portions thereof - basically whenever you run a program on your computer, it takes the data from your long-term storage and makes a copy in RAM (or again, a portion of it) which your computer then operates against - basically part of the set of commands your computer can understand is "read/write/delete data from memory at address [x]" where "[x]" is a number that is assigned to a certain part of your RAM - programs will write values into those, and using tons of layers of abstraction, use those numbers to control your computer in the way you want.

When you are using Windows (or Mac OSX), that operating system loads itself into RAM when you turn your computer on, and that program knows how to access your hard drive(s) and pull other programs out and tell your computer how it should run them.

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