249 lines
6.2 KiB
Plaintext
249 lines
6.2 KiB
Plaintext
.bp
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.np
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.ce
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CHAPTER 2 - THE EVOLUTION OF DOS
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Since its introduction, Apple DOS has
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gone through three major versions.
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All of these versions look
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very much the same on the surface.
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All commands supported by DOS 3.3
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are also supported in 3.2 and 3.1.
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The need for additional versions has
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been more to fix errors in DOS and to
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make minor enhancements than to
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provide additional functionality.
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Only DOS 3.3 has offered any major
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improvement in function; an increase
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in the number of sectors that will
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fit on a track from 13 to 16.
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.sp1
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DOS 3 - 29 June 1978
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.br
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DOS 3.1 - 20 July 1978
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The first release of DOS was
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apparently a victim of a rush at
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Apple to introduce the DISK II. As
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such, it had a number of bugs. With the
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movement towards the APPLE II PLUS
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and the introduction of the AUTOSTART
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ROM, a new release was needed.
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.sp1
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DOS 3.2 - 16 February 1979
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Although DOS 3.2 embodied more
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changes from its
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predecessor than any other release of
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DOS, 90% of the basic structure of DOS 3.1
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was retained. The major differences
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between DOS 3.1 and 3.2 and later versions of DOS
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are listed below:
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- NOMON C,I,O is the initial default
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under DOS 3.2. MON C,I,O was the
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default under DOS 3.1.
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- Input prompts (>,],*) are echoed
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when MON O is in effect, not under
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MON I as was the case under 3.1.
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- When a DOS command was entered from
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the keyboard, DOS executed it and
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then passed a blank followed by a
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carriage return to BASIC under 3.1. Under 3.2
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only a carriage return is passed.
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- Under 3.2, certain commands may not
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be entered from the keyboard but may
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only be used within a BASIC program
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(READ, WRITE, POSITION, OPEN,
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APPEND).
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- Under 3.2, when LOADing an APPLESOFT program,
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DOS automatically
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converts from APPLESOFT ROM format to
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APPLESOFT RAM format if the RAM version of
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BASIC is in use and vice versa.
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- DOS 3.1 could not read lower case
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characters from a text file; DOS 3.2
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can.
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.bp
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- Some DOS commands are allowed to
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create a new file, others will not.
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Under DOS 3.1, any reference to a
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file that didn't exist, caused it to
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be created. This forced DOS 3.1 to
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then delete it if a new file was not
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desired. (LOAD XYZ under 3.1 if XYZ
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did not exist, created XYZ, deleted
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XYZ, and then printed the file not
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found error message.) Under 3.2, OPEN
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is allowed to create a file if one
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does not exist, but LOAD may not.
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- Under 3.1, exiting to the monitor
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required that the monitor status
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register location ($48) be set to
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zero before reentering DOS. Under DOS
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3.2 this is no longer necessary.
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- The Read/Write-Track/Sector (RWTS)
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section of DOS disables interrupts
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while it is executing. Under 3.1,
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RWTS could be interrupted by a
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peripheral while writing to a disk,
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destroying the disk.
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- The default for the B (byte offset) keyword is 0
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under 3.2.
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- DOS was reassembled for 3.2 causing most of
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its interesting locations and
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routines to move slightly. This
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played havoc with user programs and
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utilities which had DOS addresses
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built into them.
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- Additional file types (beyond
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T, I, A, and B) are defined within
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DOS 3.2, although no commands yet
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support them. The new types are S,
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R, a new A, and a new B.
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R has subsequently been used by the
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DOS TOOLKIT for relocatable object
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module assembler files. At present,
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no other use is made of these
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extra file types.
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- Support was added under 3.2 for the
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AUTOSTART ROM.
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- All files open when a disk full
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condition occurs are closed by DOS
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3.2.
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- As with each new release of DOS,
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several new programs were added to
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the master diskette for 3.2. Among
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these was UPDATE 3.2, a replacement
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for MASTER.CREATE, the utility for
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creating master diskettes. UPDATE
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3.2 converts a slave into a master
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and allows the HELLO file to be
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renamed.
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.br
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DOS 3.2.1 - 31 July 1979
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DOS 3.2.1 was essentially a
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"maintenance release" of DOS 3.2.
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Minor patches were made to RWTS and
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the COPY program to correct a timing
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problem when a dual drive copy was
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done. Additional delays were added
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following a switch between drives.
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.bp
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DOS 3.3 - 25 August 1980
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Introduced in mid 1980 as a
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hardware/software upgrade from DOS
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3.2.1, the DOS 3.3 package includes
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new bootstrap and state ROM chips for
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the disk controller card which
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provide the capability to
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format, read, and write a
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diskette with 16 sectors.
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(These ROMs are the
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same ones used with the LANGUAGE
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SYSTEM.)
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This improvement
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represents almost a 25% increase in
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available disk space over the old
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13 sector format.
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Also included in the 3.3
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package is an updated version of the
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DOS manual, a BASICS diskette (for 13
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sector boots), and a master diskette.
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Although the RWTS portion of DOS was
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almost totally rewritten, the rest of
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DOS was not reassembled and only
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received a few patches:
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- The initial DOS bootstrap loader
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was moved to $800 under 3.3. It was
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at $300 under 3.2. In addition, as
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stored on the diskette (track 0
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sector 0) it is nibbilized in the
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same way as all other sectors under
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3.3.
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- A bug in APPEND which caused it to
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position improperly if the file was a
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multiple of 256 bytes long was fixed
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under 3.3.
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- A VERIFY command is internally
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executed after every SAVE or BSAVE
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under 3.3.
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- All 4 bytes are used in the Volume
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Table Of Contents (VTOC) free sector bit map when
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keeping track of free sectors. This
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allows DOS to handle up to 32 sectors
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per track. Of course, RWTS will only
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handle 16 sectors due to hardware
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limitations.
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- If a LANGUAGE CARD is present, DOS
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stores a zero on it at $E000 during
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bootstrap to force the HELLO program
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on the master diskette to reload
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BASIC.
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- DOS is read into memory from the
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top down (backwards) under 3.3 rather than the
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bottom up. Its image is
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still stored in the same order on the
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diskette (tracks 0, 1, and 2),
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however.
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- Additional programs added to the
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master diskette under 3.3 include
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FID, a generalized file utility which
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allows individual files or groups of
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files to be copied, MUFFIN, a
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conversion copy routine to allow 3.2
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files to be moved to 16 sector 3.3
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diskettes, BOOT 13, a program which
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will boot a 13 sector diskette,
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and a new COPY program
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which will also support single drive
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copies.
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- Under 3.2, speed differences in
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some drives prevented their use
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together with the DOS COPY program.
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Because the COPY program was rewritten
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under 3.3, that restriction no longer
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applies.
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.br
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.pi0
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.in0
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.ps1
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.nx ch3.1
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