Fred2718 t1_j6isch7 wrote on January 30, 2023 at 5:10 PM

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.

d4rkh0rs t1_j6iw1nd wrote on January 30, 2023 at 5:33 PM

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

Fred2718 t1_j6izhk0 wrote on January 30, 2023 at 5:54 PM

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

d4rkh0rs t1_j6jk32l wrote on January 30, 2023 at 8:01 PM

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.

Fred2718 t1_j6jpki5 wrote on January 30, 2023 at 8:35 PM

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.