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Page References

Incoming links Outgoing links
OSS A+ 2
OSS A+ 2

Version management

Difference between version and

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!!!OSS OS/A+ Version 2.10; Copyright (C) 1981-1983 OSS, Inc.
!!! OSS/A+ Version 2
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!!ATR image
* [OSS OS/A+ Version 2.10|OSS_OS-Aplus_v2.atr]
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!!Manuals
* [OSS OS/A+ manual|OS_A_Plus_manual.pdf] ; size: 7.2 MB ; thanks to Atarimania! :-)
* [OSS OS/A+ manual June 1983|OS_A_Plus_June_83_rev.pdf] ; size: 4.9 MB ; thanks to Atarimania! :-)
* [OSS OS/A+ bug sheet|OS_A_Plus_Bug_Sheet.pdf] ; thanks to Atarimania! :-)
( Information from the OSS/A+ 4.0 Handbook )
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(Information from the OSS/A+ 4.0 Handbook)
!!Version 2 File Structure
!! Version 2 File Structure
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wrote Atari's [DOS]). For reasons known best to Atari, OSS were
wrote Atari's DOS). For reasons known best to Atari, OSS were
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number in square brackets ~[thus~].
number in square brackets \[thus\].
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!!DATA SECTORS
!!! DATA SECTORS
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A Data Sector is used to contain the file's data bytes. Each 128 ~[256~] byte data sector is organized to hold 125 ~[253~] bytes of data and three bytes of control. The data bytes start with the first byte (byte 0) in the sector and run contiguously up to, and including, byte 124 ~[252~]. The control information starts at byte 125 ~[253~]
A Data Sector is used to contain the file's data bytes. Each 128 \[256\] byte data sector is organized to hold 125 \[253\] bytes of data and three bytes of control. The data bytes start with the first byte (byte 0) in the sector and run contiguously up to, and including, byte 124 \[252\]. The control information starts at byte 125 \[253\]
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The sector byte count is contained in byte 127 ~[255~]. This value is the actual number of data bytes in this particular sector. The value may range from zero (no data) to 125 ~[253~] (a full sector). Any data sector in a file may be a short sector (contain less than 125 ~[253~] data bytes).
The sector byte count is contained in byte 127 \[255\]. This value is the actual number of data bytes in this particular sector. The value may range from zero (no data) to 125 \[253\] (a full sector). Any data sector in a file may be a short sector (contain less than 125 \[253\] data bytes).
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The left six bits of byte 125 ~[253~] contain the file number of the file. This number corresponds to the location of the file's entry in the Directory. Directory entry zero in Directory sector $169 has a file number of zero. Entry one in Directory sector $169 has a file number one, and so forth. The file number value may range from zero to 63 ($3F). The file number is used to insure that the sectors of one file do not get mixed up with the sectors of another file.
The left six bits of byte 125 \[253\] contain the file number of the file. This number corresponds to the location of the file's entry in the Directory. Directory entry zero in Directory sector $169 has a file number of zero. Entry one in Directory sector $169 has a file number one, and so forth. The file number value may range from zero to 63 ($3F). The file number is used to insure that the sectors of one file do not get mixed up with the sectors of another file.
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The right two bits of byte 125 ~[253~] (and all eight bits of byte 126 ~[254~]) are used to point to the next data sector in the file. The ten bit number contains the actual disk sector number of the next sector. Its value ranges from zero to 719 ($2CF). If the value is zero then there are no more sectors in the file sector chain. The last sector in the file sector chain is the End-Of-File sector. The End-of-File sector will almost always be a short sector.
The right two bits of byte 125 \[253\] (and all eight bits of byte 126 \[254\]) are used to point to the next data sector in the file. The ten bit number contains the actual disk sector number of the next sector. Its value ranges from zero to 719 ($2CF). If the value is zero then there are no more sectors in the file sector chain. The last sector in the file sector chain is the End-Of-File sector. The End-of-File sector will almost always be a short sector.
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!!DISK DIRECTORY
!!! DISK DIRECTORY
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[{Image src='version2dir.png'}]
[{Image src='version2dir'}]
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!!VOLUME TABLE OF CONTENTS (VTOC)
!!! VOLUME TABLE OF CONTENTS (VTOC)
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The sector bit map is a contiguous string of 90 bytes, each of which contains eight bits. There are a total of 720 (90 x 8) bits in the bit map -- one for each possible sector on an 810 diskette. The 90 bytes of bit map start at VTOC byte ten ($OA). The leftmost bit ($80 bit) of byte $OA represents sector zero. The bit just to the right of the leftmost bit ($40 bit) represents sector one. The rightmost bit (bit $01) of byte $63 represents sector 719.
The sector bit map is a contiguous string of 90 bytes, each of which contains eight bits. There are a total of 720 (90 x 8) bits in the bit map -- one for each possible sector on an 810 diskette. The 90 bytes of bit map start at VTOC byte ten ($OA). The leftmost bit ($80 bit) of byte $OA respresents sector zero. The bit just to the right of the leftmost bit ($40 bit) represents sector one. The rightmost bit (bit $01) of byte $63 represents sector 719.
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!!Picture
[{Image src='OS_A_Plus_d7.jpg' width=395 height=395 }]
OSS/A+ Version 2 diskette ; thanks to Atarimania! :-)
This page (revision-14) was last changed on 03-Feb-2023 15:21 by Roland B. Wassenberg  Top