what is the difference between file and random access file?
A random access file is a file where you can "jump" to anywhere within it without having to read sequentially until the position you are interested in.
For example, say you have a 1MB file, and you are interested in 5 bytes that start after 100k of data. A random access file will allow you to "jump" to the 100k-th position in one operation. A non-random access file will require you to read 100k bytes first, and only then read the data you're interested in.
Hope that helps.
Clarification: this description is language-agnostic and does not relate to any specific file wrapper in any specific language/framework.
Almost nothing these days. There used to be a time in certain operating systems where there were different types of files - some of which could be accessed randomly (at any point in the file) and others which could only be accessed sequentially. This made more sense when you were using a sequential medium such as tape. Any file system worth its salt these days only supports random access.
来源：https://stackoverflow.com/questions/905706/what-is-the-difference-between-file-and-random-access-file