[Info-vax] Assembly languages

[gah4]

On Monday, April 11, 2022 at 8:00:45 AM UTC-7, Dennis Boone wrote:

> > That is obviously incorrect. Every disk used today is divided into 
> > blocks. So that is what a file on a disk is, in the end. And that is not 
> > the same as a string of bytes. The string of bytes abstraction is 
> > implemented on top of this.

> Er, not a very convincing argument. In that vein, every magnetic media 
> disk used today is a string of flux transitions. The bytes and blocks 
> abstraction are implemented on top of this. 

Blocks are real on floppy disks, even today.  (Well, they might not be
so easy to find.)  I suspect, though, that on the usual hard disk these
days, that blocks might be mostly virtual. 

Traditionally, the important part of disk I/O is the write splice, where
one starts and stops writing a block. The controller/drive has to 
start writing just after the appropriate block header, and stop within
the gap after the block. But as internal disk buffers got bigger, it is
now possible for a whole disk track to go into the buffer.  Though
last I knew, disks knew how to start reading in the middle of a track,
such that it could supply blocks to the system before reading the
whole track. 

Some earlier drives are likely still running, though.

Note that the rotational speed of disks hasn't changed much over
about 50 years, and rotational latency is a big part of disk reading.