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