sequential disk read speed

I am learning about database systems, and I am reading a book called "Physical Database Design".

It gets to a bit about a large sequential access (e.g. for a full table scan), and does the following:

It says "Since most disk systems use prefetch buffers to speed up table scans, we
assume a 64 KB prefetch block"

So to calculate the time for a full table scan, it multiples the number of 64KB blocks by the time it takes to seek and read (2.02ms). In other words, it is seeking each 64KB block.

Why can a disk only read 64KB at a time? Is this a valid assumption? Is this a disk limitation or a file system limitation?

Thanks Received on Wed Aug 20 2008 - 19:36:41 CDT