POWR-DISK Owner's Manual

The Model 100 and Tandy 200 have different values for MAXRAM.  Diagrammatically,
it helps to visualize RAM memory in "neighborhoods".

								Manual Page 29
								--------------

	 ================  Top Address = 65535
	|                |
	|    Reserved    |
	|     System     |
	|     Memory     |
	|                |
	|================| MAXRAM  100 = 62960
	|                |         200 = 61104
	|  User Memory   |
	| (Files, etc.)  |
	|                |
	 ================  Lowest RAM address 100/24K = 40960
					      100/32K = 32768
					      200/24K = 40960

A much more detailed chart could also show the relative locations of BA, DO,
and CO files; the location of the PASTE buffer, etc.  Everything changeable
that the computer "knows", resides somewhere in system memory or user memory.


Machine Language Memory Usage

Machine-language programs for the Model 100/200 must always run from the same
addresses.  In other words, it is insufficient to specify that they reside
"somewhere" in user memory.  The designers of the 100/200 operating systems
made provision for fixed locations: "high memory".  There is a boundary pointer
called HIMEM, that is equal to, or lower than MAXRAM.  No files, variables, or
data will reside there, since it is reserved for machine language programs.
Unless you (or a program) changes HIMEM, it is set the same as MAXRAM.  The
CLEAR command can change the HIMEM value [allowing for programs of different
sizes to run in this reserved area, and to "kill" such programs.]

Because the Model 100/200's RAM is scarce nearly every machine language program
uses the exact same locations, those directly below MAXRAM, for their "running
position" in memory.  It is possible to design two or more specific machine
language programs to share the reserved memory area, but it is impossible to do
this in general.  As a result if you want to run more than one machine language
program, [unless you can relocate one or the other,] you are out of luck.

Diagrammatically, HIMEM appears as follows:

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								--------------


[Chart on following page... - ed.]
POWR-DISK Owner's Manual

	 ================  Top Address = 65535
	|                |
	|    Reserved    |
	|     System     |
	|     Memory     |
	|                |
	|================| MAXRAM  100 = 62960
	|                |         200 = 61104
	|    Reserved    |
	|     Memory     |
	|                |
	|================  Value of HIMEM set by CLEAR statement
	|                |
	|      User      |
	|     Memory     |
	|  (Files, etc.) |
	|                |
	 ================  Lowest RAM address


CO Files

[There are various interpretations of the meaning of "CO".  Some writers say
this is an acronym for "Command", some say it stands for "Compiled".  The POWR-
DISK manual uses "Command", which is unsatisfactory to the editor, so I changed
it! - ed.]

The Model 100/200's designers anticipated the clashing of machine language
programs.  They created .CO files.  A CO file exists in user memory with other
files and never clashes, but it cannot be "run" like a BASIC program.  Instead
it is like a "snapshot" of the reserved memory area, containing a non-executing
image (copy) of a runnable machine language program.  When you select a CO file
on the main menu and press <ENTER>, the computer (1) copies the "snapshot" into
the reserved memory area, and (2) begins execution of that copy.

[The "snapshot" image is not required while the program is executing. - ed.]

On the Tandy 200, spreadsheet files are also CO files.  This confuses the issue
because they are not "programs".  This appendix does not discuss the makeup of
the spreadsheet CO files used by MSPLAN.

There are some implications to CO files:
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								--------------

- HIMEM must be set low enough to load the CO file into reserved memory before
running it.  If it is not, the computer will just beep at you, and return to
the main menu.

- In order to run a CO file from the menu, you must have enough memory to store
it TWICE: once in the CO file, and once in the reserved memory area.  [A 2500
byte CO file will use 5000 bytes while it is actually loaded and running. ...
FLOPPY.CO at slightly over 3500 bytes, actually uses up more than 7000 bytes of
RAM space when executing, if it is also left stored in the image file, where it
appears on the menu. - ed.]
POWR-DISK Owner's Manual

- Once a CO file has been copied into the reserved memory area, it is often
possible to remove the CO file image that appears on the menu, and still
execute the program.

[POWR-D.CO, once loaded and operational with the START.BA program, can be
removed from RAM with the Kill command, and in fact, the abbreviated version of
START.BA in PDSK03.200 does just that; removing both POWR-D.CO and START.BA
after POWR-DISK is loaded and operational. -ed.]


Enter POWR-DISK

In some respects, POWR-DISK confuses the RAM management issue even further,
because it lowers MAXRAM when it is active to protect itself, so that the CLEAR
command in BASIC cannot wipe it out.  Diagrammatically, the memory with POWR-
DISK installed, looks like this:

	 ================  Top Address = 65535
	|                |
	|    Reserved    |
	|     System     |
	|     Memory     |
	|                |
	|================| Default MAXRAM  100 = 62960
	|                |         	   200 = 61104
	|   POWR-DISK    |
	|                |
	|================| NEW MAXRAM
	|                |
	|    Reserved    |
	|     Memory     |
	|                |
	|================| HIMEM
	|                |
	|      User      |
	|     Memory     |
	|  (Files, etc.) |
	|                |
	 ================  Lowest RAM address

For dealing with most BASIC program, lowering MAXRAM is a good technique.  How-
ever, machine language programs cannot recognize a different MAXRAM or run in
other locations.  Thus, it becomes necessary to relocate either the other m/l
program, or, when this is not possible, relocate POWR-DISK.

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								--------------

Relocation actually changes a machine language program to run in different
addresses.  A program so relocated can reside in the reserved memory area in
the diagram above.  The CO file does not need to sit in RAM, since POWR-DISK
can copy it directly from the TDD into reserved memory -- a feat beyond the
capabilities of FLOPPY.CO.

Further, when dealing with machine language programs that cannot be relocated,
POWR-DISK Owner's Manual

POWR-DISK itself can be relocated.  Diagrammatically, the memory then looks as
follows:

	 ================  Top Address = 65535
	|                |
	|    Reserved    |
	|     System     |
	|     Memory     |
	|                |
	|================| Default MAXRAM  100 = 62960
	|                |         200 = 61104
	|    Machine     |
	|    Language    | <-- POWR-DISK was here
	|    Program     |       |
	|                |       |
	|================|       |
	|                |       |
	|   POWR-DISK    | <-- Relocated to here
	|                |
	|================| New (Relocated) MAXRAM
	|                |
	|      User      |
	|     Memory     |
	|      Area      |
	|                |
	 ================  Lowest RAM address

Note that the HIMEM address is usually the same as MAXRAM when POWR-DISK has
been relocated, so there is no reserved memory area visible -- but there still
could be.  The machine language program sitting above POWR-DISK does not "know"
that MAXRAM has been moved lower; it runs thinking that it is in the reserved
memory area.

This subject is complex; if you are lost, don't worry.  If you have difficulty
accommodating a machine language program for use with POWR-DISK, ask a knowled-
geable friend or [leave a message on the Model 100 Forum message board].



			   [End of POWR-DISK Manual.]

[Acroatix also sent out a newsletter to registered owners of the POWR-DISK
program, which offered tips and general ideas on use of the program, as well as
advising customers of updates, update policy, and discussing new software that
was available.  As far as I know, only one issue of the newsletter was ever
produced.

Significant comments from the Newsletter will be found in the next file in this
series. - ed.]