Re: Appleworks files on Apple II as

[wyanttr@spoc.dnet.dupont.com (Tom Wyant)]

"Tom Zuchowski" <tjz@mindspring.com> wrote:

> I'm curious, why do you believe that a GS is more efficient
> at copying ProDOS files than any other Apple II model?  In
> every case you're most severely limited by disk speed,
> aren't you?

Well, yes and no. Disk speed has three components:
* Seek time, that is, the amount of time required to get the
  heads over the right track;
* Rotational latency, that is, the amount of time required
  for the right sector to come around to where the heads are;
* Transfer time, that is, the amount of time required for all
  the data to pass under the heads.

Seek time and rotational latency are the largest components 
of the time required to get data off a disk. Moreover, under 
reasonable conditions (right interleave factor, system not 
totally bogged down, ...), YOU ONLY NEED TO INCUR THEM ONCE 
PER DISK I/O, NO MATTER HOW MANY SECTORS YOU READ OR WRITE. 
Well, for a really big I/O you will need to switch to the 
next track, but again that's faster than the average seek. So 
the bottom line is, THE MORE DATA YOU CAN MOVE AT A TIME, THE 
FASTER YOUR I/O WILL BE, EVEN GIVEN THE SAME HARDWARE.

Example: Under ProDos 16 v something-or-other, with 512K, 
FASTCOPY was the fastest way for me to make disk copies; much 
faster than the finder. Part of the reason (more on that 
below) is that the finder had less memory to play with.

Another thing that can affect the throughput of a copy 
operation is how smart the application doing the copy is. The 
garden-variety copy simply opens the respective files and 
copies bytes. This is inefficient, because three separate 
sectors need to be accessed to extend a ProDos file:
* The volume bitmap, to find a free sector for the new data,
* The sector index for the file (I forget what it's called in
  ProDos), to attach the new sector to the file,
* The newly-allocated sector, to hold the new data.
Copy operations can be speeded up enormously by smarter copy 
programs, which do such things as pre-allocating the space 
for the output file, as contiguously as possible, to cut down 
on the number of seeks done.

ProDos 16 and early GS/OS did garden-variety file copies; I 
believe that the ProDos 8 file utilities do also. Modern 
versions of the Finder, however, have been optimized to do 
more efficient copy operations, and are MUCH faster.

Tom Wyant                     The opinions expressed in this
wyanttr@spoc.dnet.dupont.com  document are those of the 
twyant@erols.com              author, except for the                               
                              following, which is
                              William Shakespeare's:
                        "The first thing we do is, we'll kill
                        all the lawyers."
                        Henry VI, Part II, Act 4, Scene 2