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Chapter 4

MOVEDOS DOS RELOCATION SOFTWARE

The software provided with the Saturn 64K and 128K boards

enables one to take advantage of a portion of the RAM present on

these cards by moving DOS (DOS 3.2 or 3.3) up into the board,

thus freeing up approximately 10K of memory for user programs.

In a 48K system, DOS normally resides at the top of the

48K of RAM, occupying 10.5K of RAM (from $9~00 to $BFFF). HIMEM

is set to reflect the presence of DOS (HIMEM = $9600). As long

as DOS is resident, the memory occupied by it is not available

for program use. The program MOVEDOS, provided with the Saturn

64K and 128K boards, frees up 10K of the memory space normally

occupied by DOS, while at the same time keeping DOS in the

system, and available. This is accomplished by relocating

(moving) DOS up into the Saturn RAM board and making appropriate

modifications to the system so as to be able to communicate with

this relocated DOS. DOS is kept in the 64K or 128K memory board,

and used when required.

Essentially DOS is stored in a portion of the Saturn 64K or

128K board which is disabled (turned off) until it is needed.

As a result, when DOS is not being used, it isn’t sitting in

lower memory, taking up valuable space. When DOS is required, it

is used in the following manner.

1. The part of the Saturn 64K or 128K board which contains

DOS is enabled (turned on). This results in BASIC (Integer

or Applesoft) being disabled (turned off) and no longer

resident.* This poses no problem, since BASIC is not

required by DOS during the time a DOS command is being

executed.

2. The desired DOS command is executed by the relocated

DOS, now resident in the system.

3. The portion of the Saturn RAM board which contains DOS

is disabled (turned off) . The BASIC which had been

present prior to the call to DOS is re—enabled, and

control is returned to the program from which DOS was

called.

In this way, as far as the user is concerned, DOS is present

in the system and there is 10K more memory available for program

use. In addition, the user has access to either BASIC (Integer

or Applesoft), since either of these can be present in the Saturn

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

* Note: This occurs because the relocated DOS actually shares

the memory space occupied by BASIC. ($DOOO—$FFFF)

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