Re: Prodos 8 vs Prodos 16

[dempson@actrix.gen.nz (David Empson)]

Jerome Vernet <jeromevernet@hotmail.com> wrote:

> I have an Apple IIGS ROM01, and found lot of disk image on internet to run
> it. Some of these disk start with a Prodos 8 (usually 2,0,3) or Prodos 16.
> 
> What are the difference between Prodos 8 and Prodos 16 ?

ProDOS-8 is the 8-bit ProDOS operating system which runs on everything
from a 64K Apple ][+ onward.  It was originally just called "ProDOS",
and the earliest versions (1.0.x) can run in a 48K ][+, but BASIC.SYSTEM
isn't available in this configuration (and many other applications won't
work either).  The name was changed as of ProDOS-8 1.2, when they added
special support for the IIgs, and to distinguish it from ProDOS-16.

ProDOS-16 is a 16-bit operating system which only runs on the IIgs.  It
is a modified version of ProDOS-8.

The main technical difference between the two (on a IIgs) is that
ProDOS-8 runs almost entirely in "emulation mode" on the CPU, i.e.
treating it like a souped up 65C02, while ProDOS-16 runs in "native
mode" (switching to emulation mode only when required, e.g. when using
device drivers).

ProDOS-16 was required up until about 1988 if you wanted to run native
16-bit IIgs applications.  It also supported 8-bit applications, by
launching ProDOS-8 as necessary (ProDOS-16 was loaded back into memory
when you quit from the 8-bit application).

In 1988, Apple replaced ProDOS-16 with GS/OS (as of version 4.0 of the
Apple IIgs system software).  GS/OS is compatible with ProDOS-16
applications, but is a complete rewrite of the operating system in
native mode, and it performs a lot better than ProDOS-16.

GS/OS also supports the "launch ProDOS-8" mechanism (and it is much
faster to return to GS/OS than it was to return to ProDOS-16).

> More over, where to find the latest version of Prodos and BASIC-SYSTEM ?

ProDOS-8 2.0.3 and BASIC.SYSTEM 1.5.1 (?) are the latest versions.  They
are both supplied with IIgs System 6.0.1.  (I can't check the latter
right now, because Bernie to the Rescue isn't working, for some reason.)

ProDOS-16's last version was 1.6, and it was supplied on IIgs System
3.2.

Each version of ProDOS-16 and GS/OS was supplied with a particular
version of ProDOS-8 on the system disk, and you cannot change it - if
you want to run a later version of P8 while still booting a 16-bit
operating system, then you need to upgrade to later version of ProDOS-16
or GS/OS.

If you are booting directly into ProDOS-8, this is not an issue.
-- 
David Empson
dempson@actrix.gen.nz