Date   : Mon, 25 Feb 1991 13:48:23 -0500
From   : Jay Sage <sage@ll.mit.edu>
Subject: Z-System

Will Rose wrote:

>> The Z system uses a standard CP/M BIOS - whatever the BIOS can handle,
>> (eg. bank switching) that the Z system will use.

I strongly second this comment.  The Z-System does not include a new BIOS; it
builds on the existing BIOS.  It can add features (cf. especially my next TCJ
column), but it never subtracts features.

Will then added:

>> The auto-install versions don't need access to the BIOS source, but as the
>> Z system uses a few K *above* the BIOS for buffers and command packages, I
>> personally would find it easier to install a system manually with BIOS
>> source available.

This comment I do not understand!  True, the Z-System must have some modules
installed in protected memory (above or within the BIOS), but this is the
case whether the system is installed manually or automatically.  The
automatic system uses a trick whose only penalty is a small amount of extra
memory usage (about 0.25K).

In no case is the manual system "easier to install", no matter whether you
have BIOS source or not.  The real limitation of a manual system is that it
is highly inflexible: whatever buffers you have built in, that's what you are
stuck with.  With the automatic system you can change the total amount of
memory used by the buffers, as well as how that memory is partitioned among
them, at any time, even right in the middle of a multiple command line
sequence.

The ability to add and remove BIOS features by exchanging virtual BIOS
(VBIOS) modules is also lost in a manual system.  In principle -- though so
far I have yet to get around to doing this on my Ampro -- one can have a
SMALLER operating system (larger TPA) with NZCOM than with a standard BIOS
installation.  One simply strips all the bells and whistles out of the CBIOS
and includes them in the virtual BIOS.  Then, when one runs an application
that is really memory hungry, one can swap in the minimum VBIOS.

By the way, not having source to the BIOS does not absolutely preclude a
manual installation.  Several installation packages have been published for
ZCPR30, and they can easily be updated for ZCPR33.  You pretty much do need a
working MOVCPM so that you can move the system down to make room above the
BIOS for the Z-System buffers.  Then you have to patch the coldboot code to
initialize those buffers.  I have done that without having any source code. 
The coldboot routines are usually pretty simple and standard, and you can
generally patch in right at the beginning anyway.  Just put the
initialization code up in high memory and have it jump to the original
coldboot code.  If anyone wants more hints on this approach, just ask.  At
one time I had this reduced to a fine art, but now I use nothing but
autoinstall systems, and so I have not thought about these details for
several years.  But if you insist, I am willing to try!

Will mentions Rick Conn's book as a resource.  Sage Microsystems has them in
stock ($20).  Will is quite right that much of the material is rather dated,
but I still find myself referring to it amazingly often.  Another resource,
especially for those doing a manual installation of ZCPR33 is my own book
(pamphlet?) called "The ZCPR33 Users Guide" ($15).  It describes the
significant new features introduced with version 3.3 of ZCPR and has a lot of
material on how to perform the installation.

-- Jay Sage