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julia999's avatar

What is the difference between random access and serial access?

Asked by julia999 (343points) November 11th, 2009

This is what my teacher told has told me, but I found it confusing:

*Serial access writes to the end of a file and the whole file is overwritten when edited (and saved).

*Random access only changes relevant date, making it more efficient than serial.

But for some reason I feel that he may be wrong about the ‘overwritten’ part, and this makes me doubt how accurate his above descriptions are.

Could someone please clarify for me?

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2 Answers

LostInParadise's avatar

I always thought that a tape drive was an example of serial data. It is possible to position a tape drive and overwrite a specific part of a file on it without altering the rest of the file.

grumpyfish's avatar

It’s partly a question of media. However, yes, if you’re dealing with a tape drive you can overwrite any given sector on the tape without affecting the rest of the tape.

The main difference between random access and serial access, IN GENERAL, is that with random access you have roughly equal time to any given address. This is true of RAM, of SSDs,etc. With a hard disk, you almost get that—within the swing of the head. So reading data serially off a hard disk is faster than randomly.

With a tape drive, you have to actually seek to where the data is—that’s what’s going on on the old-school mainframes when you see tapes spinning fast, then slowly. Reading contiguous data is significantly faster than reading random data.

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