Difference between revisions of "IDEDOS"

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[[category:Specifications]]
 
[[category:Specifications]]
  
IDEDOS is a hard disk formatting scheme designed for ZX Spectrum computers and clones. It was designed by Garry Lancaster for his [[+3e]] ROMs, and extended by Jarek Adamski to support his ZXVGS, CPM22QED and YaPaDOS operating systems.
+
IDEDOS is a hard disk formatting scheme designed for ZX Spectrum computers and clones. It was designed by Garry Lancaster for his [[+3e]] ROMs and ResiDOS RAM based operating system, and extended by Jarek Adamski to support his ZXVGS, CPM22QED and YaPaDOS operating systems.
  
 
==Format==
 
==Format==
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IDEDOS Partition entry - 64 bytes
 
IDEDOS Partition entry - 64 bytes
 
0x0000 PN PN PN PN PN PN PN PN PN PN PN PN PN PN PN PN
 
0x0000 PN PN PN PN PN PN PN PN PN PN PN PN PN PN PN PN
0x0010 PT SC SC SH EC EC EH LS LS LS LS XX XX XX XX XX
+
0x0010 PT SC SC SH EC EC EH LS LS LS LS SS V1 V2 V3 V4
 
0x0020 XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
 
0x0020 XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
 
0x0030 XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
 
0x0030 XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
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LS: largest logical sector. 32 bit little endian word.
 
LS: largest logical sector. 32 bit little endian word.
 
XX: partition type specific data.
 
XX: partition type specific data.
 +
 +
(Virtual Geometry for Disk Image partitions)
 +
SS: Sector Shift.
 +
V1: Virtual Sector Size (0-128B, 1-256B, 2-512B, 3-1024B).
 +
V2: Virtual first sector number (0 to 240).
 +
V3: Virtual heads.
 +
V4: Virtual sectors.
 
</pre>
 
</pre>
 +
 +
====Partition Types====
  
 
There are numerous partition types [http://8bit.yarek.pl/system/fs.idedos/index.html defined]
 
There are numerous partition types [http://8bit.yarek.pl/system/fs.idedos/index.html defined]
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</pre>
 
</pre>
  
====The IDEDOS System Partition Partition Table Entry====
+
=====Partition Type 0x01 - The IDEDOS System Partition=====
 
The first partition entry in the partition table is the IDEDOS system partition.
 
The first partition entry in the partition table is the IDEDOS system partition.
 
The starting head and ending head are either zero or one depending on where the partition table has been written.
 
The starting head and ending head are either zero or one depending on where the partition table has been written.
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EA: +3 BASIC editor attribute byte
 
EA: +3 BASIC editor attribute byte
 
DD: plus3dos default drive letter
 
DD: plus3dos default drive letter
??: unknown
+
??: unused
 
</pre>
 
</pre>
  
====Partition Type 0x03 - +3DOS====
+
=====Partition Type 0x03 - +3DOS=====
 
The [[+3e|+3e ROMs]] create partitions of type 0x03 i.e. [[+3DOS]] partitions. The type specific data portion of the Partition Entries for these partitions contain a [[+3DOS#XDPB|+3DOS XDPB (eXtended Disc Parameter Block)]] between 0x0020 to 0x003A and also the +3DOS drive letter to which the partition has been mapped (if any)
 
The [[+3e|+3e ROMs]] create partitions of type 0x03 i.e. [[+3DOS]] partitions. The type specific data portion of the Partition Entries for these partitions contain a [[+3DOS#XDPB|+3DOS XDPB (eXtended Disc Parameter Block)]] between 0x0020 to 0x003A and also the +3DOS drive letter to which the partition has been mapped (if any)
  
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DP: +3DOS extended disk parameter block byte
 
DP: +3DOS extended disk parameter block byte
 
DL: plus3dos drive letter
 
DL: plus3dos drive letter
??: unknown
+
??: unused
 
</pre>
 
</pre>
  
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</pre>
 
</pre>
  
====Partition Type 0xFF - Free Space====
+
=====Partition Type 0x3x - Non-CP/M Disk Image Partitions=====
 +
For partitions containing non-CP/M floppy disk images the type specific information defines a virtual geometry. More than one disk image partition can be present on each track, i.e. the partitions do not have to align to track boundaries.
 +
This is achieved by specifying a sector shift in the partition table entry. For example for a disk with 980 cylinders, 5 heads, 17 sectors per track and 512 bytes per sector, a 800kB partition takes 1600 sectors which is equal to 18 cylinders + 4 tracks + 2 sectors, so the shift for next partition is 2.
 +
 
 +
=====Partition Type 0xFF - Free Space=====
 
A Type 0xFF partition entry as created by the +3e ROMs is all blank except for the type byte and the location and size information. The type specific information is not used.
 
A Type 0xFF partition entry as created by the +3e ROMs is all blank except for the type byte and the location and size information. The type specific information is not used.

Revision as of 21:26, 27 March 2011


IDEDOS is a hard disk formatting scheme designed for ZX Spectrum computers and clones. It was designed by Garry Lancaster for his +3e ROMs and ResiDOS RAM based operating system, and extended by Jarek Adamski to support his ZXVGS, CPM22QED and YaPaDOS operating systems.

Format

Note: The following is not an official specification, it has been reverse engineered from hard disk images and information collected from various sources. The labels given to bytes are entirely arbitrary and should not be taken as the official labels.

IDEDOS supports up to 65535 partitions on a hard disk, with a theoretical maximum partition size of 2TB. However IDEDOS does not support LBA mode therefore the hard disk capacity is limited to 128GB by the limitations of CHS addressing.

8-bit vs 16-bit interfaces for Z80 based computers

Since the Z80 microprocessor has as an 8-bit data bus and IDE requires a 16-bit data bus some circuitry is required to combine a pair of 8-bit read/write operations into a single 16-bit operation. This extra circuitry increases cost and complexity in a hard disk interface so some interfaces omit this circuitry and simply treat the IDE bus as a normal 8-bit wide I/O device. This means that when any 16-bit word is read from or written to the hard disk, the upper byte is simply ignored, therefore half the hard disk's capacity cannot be utilised by computer. IDEDOS supports these halved capacity interfaces as it simply means that each hard disk sector contains 256 bytes instead of the standard 512 bytes. Software which reads from an IDEDOS formatted disk should not therefore make assumptions about the number of bytes per sector as it depends on the hardware used to format the disk.

The IDEDOS System Partition

The IDEDOS System Partition is normally the first partition on the drive located at Cylinder 0, Head 0, Sector 1 (C0/H0/S1). The specification also allows placing the system partition at Cylinder 0, Head 1, Sector 1 (C0/H1/S1) to allow an MS-DOS Master Boot Record to be present.

The IDEDOS System Partition contains the Partition Table for the drive. The Partition Table consists of a number of Partition Table Entries each 64 bytes long containing the partition type, location, size, and additional type specific information.

The first partition entry in the table describes the IDEDOS System Partition itself and contains information about the drive geometry and initialisation information for the +3e system ROMs

Partition Table Entry Format

All partition table entries conform to the following structure

IDEDOS Partition entry - 64 bytes
0x0000	PN PN PN PN PN PN PN PN PN PN PN PN PN PN PN PN	
0x0010	PT SC SC SH EC EC EH LS LS LS LS SS V1 V2 V3 V4	
0x0020	XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX	
0x0030	XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX	

Key:
PN: partition name. 16 byte unterminated text string.
PT: partition type.
SC: starting cylinder. 16 bit little endian word.
SH: starting head.
EC: ending cylinder. 16 bit little endian word.
EH: ending head.
LS: largest logical sector. 32 bit little endian word.
XX: partition type specific data.

(Virtual Geometry for Disk Image partitions)
SS: Sector Shift.
V1: Virtual Sector Size (0-128B, 1-256B, 2-512B, 3-1024B).
V2: Virtual first sector number (0 to 240).
V3: Virtual heads.
V4: Virtual sectors.

Partition Types

There are numerous partition types defined

0x00:	unused partition
0x01:	system partition
0x02:	swap partition
0x03:	+3DOS partition
0x04:	CP/M partition
0x05:	boot partition
0x0F:	movie partition
0x10:	FAT16 partition
0x20:	UZI(X) partition
0x30:	TR-DOS disk image
0x31:	+D/SAMDOS disk image
0x32:	MB-02 disk image
0x40:	ZX Spectrum +3 disk image
0x41:	Elwro 800 Junior disk image
0x48:	Amstrad CPC disk image
0x49:	Amstrad PCW disk image
0xFE:	bad disk space
0xFF:	free disk space
Partition Type 0x01 - The IDEDOS System Partition

The first partition entry in the partition table is the IDEDOS system partition. The starting head and ending head are either zero or one depending on where the partition table has been written. The drive geometry is written in the type specific data in the bytes 0x0020 to 0x0027

0x0000	50 4C 55 53 49 44 45 44 4F 53 20 20 20 20 20 20		partition name "PLUSIDEDOS      "
0x0010	01 00 00 SH 00 00 EH LS LS LS LS ?? ?? ?? ?? ??	
0x0020	NC NC NH ST SC SC MP MP BA EA ?? ?? ?? ?? ?? ??	
0x0030	DD ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ??	

Key:
NC: number of cylinders available to IDEDOS. 16 bit little endian word.
NH: number of heads.
ST: number of sectors per track.
SC: number of sectors per cylinder (equal to NH * ST). 16 bit little endian word.
MP: maximum partition. 16 bit little endian word.
BA: +3e boot colour attribute byte
EA: +3 BASIC editor attribute byte
DD: plus3dos default drive letter
??: unused
Partition Type 0x03 - +3DOS

The +3e ROMs create partitions of type 0x03 i.e. +3DOS partitions. The type specific data portion of the Partition Entries for these partitions contain a +3DOS XDPB (eXtended Disc Parameter Block) between 0x0020 to 0x003A and also the +3DOS drive letter to which the partition has been mapped (if any)

0x0000	PN PN PN PN PN PN PN PN PN PN PN PN PN PN PN PN	
0x0010	03 SC SC SH EC EC EH LS LS LS LS ?? ?? ?? ?? ??	
0x0020	DP DP DP DP DP DP DP DP DP DP DP DP DP DP DP DP	
0x0030	DP DP DP DP DP DP DP DP DP DP ?? ?? DL ?? ?? ??	

Key:
DP: +3DOS extended disk parameter block byte
DL: plus3dos drive letter
??: unused

The eXtended Disk Parameter Block data is ordered as follows

0x0020  SPT SPT BSH BLM EXM DSM DSM DRM DRM AL0 AL1 CKS CKS OFF OFF PSH
0x0030  PHM sid tps spt fsn ss  glr glf mms ff

key:
SPT: Records Per Track
BSH: Block Shift: 128 * 2^BSH
BLM: Block Mask: 128 * (BLM + 1)
EXM: Extent Mask
DSM: number of blocks - 1
DRM: number of directory entries - 1
AL0: AL0 directory bitmap
AL1: AL1 directory bitmap
CKS: size of checksum vector
OFF: reserved tracks
PSH: physical sector shift
PHM: sector size
sid: sidedness
tps: number of tracks per side
spt: number of sectors per track
fst: first sector number
ss:  (sector size / 128) - 1
glr: gap length (read/write)
glf: gap length (format)
mms: multitrack/modulation/skip
ff:  freeze flag
Partition Type 0x3x - Non-CP/M Disk Image Partitions

For partitions containing non-CP/M floppy disk images the type specific information defines a virtual geometry. More than one disk image partition can be present on each track, i.e. the partitions do not have to align to track boundaries. This is achieved by specifying a sector shift in the partition table entry. For example for a disk with 980 cylinders, 5 heads, 17 sectors per track and 512 bytes per sector, a 800kB partition takes 1600 sectors which is equal to 18 cylinders + 4 tracks + 2 sectors, so the shift for next partition is 2.

Partition Type 0xFF - Free Space

A Type 0xFF partition entry as created by the +3e ROMs is all blank except for the type byte and the location and size information. The type specific information is not used.