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

Darren wrote:

It's arbitrary. Some dbmses have a fixed block size; others allow one to
configure it as a parameter. Other systems try to read an entire track
or cylinder at a time. Whether the latter is feasible can change when
available cylinder sizes grow at different rates from available memory.

I suspect the book is giving a hypothetical just to demonstrate the
calculations involved.

Darren wrote:

It's arbitrary. Some dbmses have a fixed block size; others allow one to
configure it as a parameter. Other systems try to read an entire track
or cylinder at a time. Whether the latter is feasible can change when
available cylinder sizes grow at different rates from available memory.

I suspect the book is giving a hypothetical just to demonstrate the
calculations involved.

Darren wrote:

It's arbitrary. Some dbmses have a fixed block size; others allow one to
configure it as a parameter. Other systems try to read an entire track
or cylinder at a time. Whether the latter is feasible can change when
available cylinder sizes grow at different rates from available memory.

I suspect the book is giving a hypothetical just to demonstrate the
calculations involved.

Darren wrote:

It's arbitrary. Some dbmses have a fixed block size; others allow one to
configure it as a parameter. Other systems try to read an entire track
or cylinder at a time. Whether the latter is feasible can change when
available cylinder sizes grow at different rates from available memory.

I suspect the book is giving a hypothetical just to demonstrate the
calculations involved.

Darren wrote:

It's arbitrary. Some dbmses have a fixed block size; others allow one to
configure it as a parameter. Other systems try to read an entire track
or cylinder at a time. Whether the latter is feasible can change when
available cylinder sizes grow at different rates from available memory.

I suspect the book is giving a hypothetical just to demonstrate the
calculations involved.

Darren wrote:

It's arbitrary. Some dbmses have a fixed block size; others allow one to
configure it as a parameter. Other systems try to read an entire track
or cylinder at a time. Whether the latter is feasible can change when
available cylinder sizes grow at different rates from available memory.

I suspect the book is giving a hypothetical just to demonstrate the
calculations involved.

Darren wrote:

It's arbitrary. Some dbmses have a fixed block size; others allow one to
configure it as a parameter. Other systems try to read an entire track
or cylinder at a time. Whether the latter is feasible can change when
available cylinder sizes grow at different rates from available memory.

I suspect the book is giving a hypothetical just to demonstrate the
calculations involved.

Darren wrote:

It's arbitrary. Some dbmses have a fixed block size; others allow one to
configure it as a parameter. Other systems try to read an entire track
or cylinder at a time. Whether the latter is feasible can change when
available cylinder sizes grow at different rates from available memory.

I suspect the book is giving a hypothetical just to demonstrate the
calculations involved.

Darren wrote:

It's arbitrary. Some dbmses have a fixed block size; others allow one to
configure it as a parameter. Other systems try to read an entire track
or cylinder at a time. Whether the latter is feasible can change when
available cylinder sizes grow at different rates from available memory.

I suspect the book is giving a hypothetical just to demonstrate the
calculations involved.