CMD-HD

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CMD-HD
CMD-HD Isometric presentation
Type: Hard drive
Producer: CMD
Price: US$ 599.95-1299.95 US$
Released: 1990
Discontinued: 2001
Processor:
Memory:
OS:
Info: Various storage capacities: 20 MBytes to 2 GBytes.

The CMD-HD (actually HD Series) is an external hard disk drive for the C64 / 128 developed by Creative Micro Designs (CMD ) was produced from 1990 to around 2001.

It consists of a SCSI adapter designed for the C64 and a then commercially available internal SCSI hard disk in a housing with its own power supply unit, as well as several connections for operation on the C64 / 128 and a SCSI Port for additional SCSI devices.

It works with JiffyDOS, but its speed advantage can only be used if JiffyDOS is installed in the computer's Kernal. Internally it works with the so-called Boot-ROM, which is housed in an EPROM and the HD-DOS in the system partition.

The CMD-HD offers a parallel connection which establishes the connection to a RAMLink and increases the transmission rate even further. As a cable for the parallel connection, those of the external floppies from the Atari-ST fit.

The drives 1541, 1571, 1581 can be emulated, which are created as partitions on the hard disk. Native partitions can also be created, the size of which can be freely defined by the user in 256 - block steps. A native partition can have a maximum of 16 Mbytes. ([1 to 255] tracks * 256 blocks or sector s * 256 bytes). A total of 255 partitions can be set up (partition no. 0 is already occupied by the system partition). Thus, the HD-DOS can manage a maximum of 4 GBytes. However, you need the last published Boot ROM version (2.80) to be able to operate a hard disk with a capacity of more than 1 GByte.

The CMD-HD was available with different storage capacities from 20   MBytes to 2   GBytes. The first hard drives by CMD were sold in 1990, 20   MByte for about US $ 599.95, 40   MByte for US $   799.95 and 100 MByte for US $ 1299.95. From the mid-1990s, there were also models with a capacity of 1 GB.

Additional SCSI devices can be connected to the SCSI connection. This was achieved with additional hard drives to increase capacity, the Zip drives popular in the late 1990s, and CD-ROM drives. With the software CDROM-Commander , the latter gave the user the option of extracting disk image s from data CDs directly on the C64 onto the hard disk. There was also a program that could play audio CDs. The audio sound must be tapped at the audio output of the CD-ROM drive.

It is possible to replace the internal SCSI hard disk with a CF card (with SCSI-IDE adapter and IDE-CF card reader).

In addition, the CMD-HD offered a real-time clock, which was buffered by a battery.



Pictures[edit]

CMD-HD front view
CMD-HD rear view
CMD-HD board (inside view)
CMD-HD circuit board section with the battery


Partition and file formats[edit]

With HD track and sector access, it is important to remember that the track and sector layout conforms to the norm of the partition type in which the access takes place. This method allows the HD to become compatible. If an access occurs in an emulation mode partition, the track and sector layout of the partition is identical to the drive it is emulating. The tables in this section determine which tracks and sectors are present in each partition type and where the header, BAM and directory blocks are located. This section also provides information about the BAM format and directory entries, as well as the format of the various file types.

1541 emulation mode partitions[edit]

Sectors per track[edit]

SECTORS PER TRACK (1541 EMULATION MODE)
TRACKING AREA SECTOR AREA TOTAL
1 - 17 0 - 20 21
18 - 24 0 - 18 19
25 - 30 0 - 17 18
31 - 35 0 - 16 17

Directory header[edit]

HEADER (1541 EMULATION MODE)
TRACK 18 SECTOR 0
BYTE CONTENT DESCRIPTION
0 18 Track of the first directory block
1 1 Sector of the first directory block
2 65 ASCII character A for format type
3 0 1541 emulation mode
4 - 143
144 - 161 Disk name, padded with shifted spaces
162 - 163 Disk ID
164 160 Shifted spaces
165 50 ASCII representation of 2 for the DOS version
166 65 ASCII representation of A the format type
167-170 160 Shifted spaces for separation
171 - 220 0 zeros - reserved
221-255 0 zeros reserved

BAM (first block)[edit]

BAM (1541 EMULATION MODE)
TRACK 18 SECTOR 0
BYTE CONTENT DESCRIPTION
0
1
2 65 ASCII character A for format type
3
4 - 143 BAM for tracks 1-35 (4 bytes per track)
144 - 161
162 - 163 Disk ID
164
165
166
167-170
171 - 220
221-255

BAM (first Block)[edit]

BAM (1541 EMULATIONS-MODUS)
SPUR 18 SECTOR 0
BYTE DESCRIPTION
0 Number of free sectors on the track
1 Number of unused blocks for sectors 0-7
2 Number of unused blocks for sectors 8-15
3 Number of unused blocks for sectors 16-23
NOTES: The LSB (low bit) in each byte (1-3) shows the status of the lowest sector that is covered by
the byte. A binary value of 1 indicates that the sector is free, 0 indicates
that it is occupied.

1571 emulation mode partitions[edit]

Sectors per track[edit]

SECTORS PER TRACK (1571 EMULATION MODE)
TRACKING AREA SECTOR AREA TOTAL
1 - 17 0 - 20 21
18 - 24 0 - 18 19
25 - 30 0 - 17 18
31 - 35 0 - 16 17th
36 - 52 0 - 20 21
53 - 59 0 - 18 19
60 - 65 0 - 17 18
66 - 70 0 - 16 17th

Directory header[edit]

HEADER (1571 EMULATION MODE)
TRACK 18 SECTOR 0
BYTE CONTENT DESCRIPTION
0 18 Track of the first directory block
1 1 Sector of the first directory block
2 65 ASCII character A for format type
'3' '128' '1571 emulation mode'
4 - 143
144 - 161 Disk name, padded with shifted spaces
162 - 163 Disk ID
164 160 Shifted spaces
165 50 ASCII representation of 2 for the DOS version
166 65 ASCII representation of A the format type
167-170 160 Shifted spaces for separation
171 - 220 0 zeros - reserved
221-255

BAM (first block)[edit]

BAM (1571 EMULATION MODE)
TRACK 18 SECTOR 0
BYTE CONTENT DESCRIPTION
0
1
2 65 ASCII character A for format type
3
4 - 143 BAM for tracks 1-35 (4 bytes per track)
144 - 161
162 - 163 Disk ID
164
165
166
167-170
171 - 220
'221 - 255' 'Number of free sectors for tracks 36-70 - one byte per track'

BAM (further blocks)[edit]

BAM (1571 (PAGE 2) EMULATION MODE)
TRACK 53 SECTOR 0
BYTE CONTENT DESCRIPTION
0 - 104 BAM for tracks 36-70 (3 bytes per track)
105 - 255 0 zeros - reserved

BAM input format[edit]

BAM INPUT FORMAT (1571 (page 1) EMULATION MODE)
Byte format 4-143 on track 18, sector 0
4 bytes per track: Bytes 4-7 cover the track 1, bytes 8-11 cover track 2, ...
BYTE DESCRIPTION
0 Number of free sectors on the track
1 Number of unused blocks for sectors 0-7
2 Number of unused blocks for sectors 8-15
3 Number of unused blocks for sectors 16-23
NOTES: The LSB (low bit) in each byte (1-3) shows the status of the lowest sector that is covered by
the byte. A binary value of 1 indicates that the sector is free, 0 indicates
that it is occupied.

BAM input format[edit]

BAM-INPUT FORMAT (1571 (page 2) EMULATION-MODE)
Byte format 0-104 on track 53, sector 0
3 bytes per track: Bytes 0-2 cover track 36, bytes 3-5 cover track 37, ...
BYTE DESCRIPTION
0 Number of unused blocks for sectors 0-7
1 Number of unused blocks for sectors 8-15
2 Number of unused blocks for sectors 16-23
NOTES: The LSB in each byte (0-2) is used to indicate the status of the lowest sector that is
covered by the byte. A binary value of 1 indicates that the sector is free
. A binary value of 0 indicates that the sector is occupied. In bytes 221-225 of track
18, sector 0, the associated byte for the number of free sectors is stored.

1581 emulation mode partitions[edit]

Sectors per track[edit]

SECTORS PER TRACK (1581 EMULATION MODE)
AREA SECTOR AREA TOTAL NUMBER
1 - 80 0 - 39 40


Directory header[edit]

DIRECTORY HEADER (1581 EMULATION MODE)
TRACK 40, SECTOR 0
BYTE CONTENT DESCRIPTION
0 40 Track of the first directory block
1 3 Sector of the first directory block
2 68 ASCII characters from D for format type
3 0 Reserved
4 - 21 Disk name, padded with shifted spaces
22-23 Disk ID
24 160 Shifted spaces for separation
25 51 ASCII characters of 3 for DOS version
26 68 ASCII characters from D for format type
27-28 160 Shifted spaces for separations
29 - 255 0 zeros reserved

BAM (first block)[edit]

BAM BLOCK1 (1581 EMULATION MODE)
TRACK 40, SECTOR 1
BYTE CONTENT DESCRIPTION
0 40 Track of the next BAM block
1 2 Sector of the next BAM block
2 68 ASCII characters from D for DOS version
3 187 Complement of the version number
4 - 5 Disk ID
6 192 Not used by the HD (1581 default)
7 0 Tag for auto-load file
8-15 0 Reserved
16-255 BAM for tracks 1-40 (6 bytes per track)

Partition and file format comparison[edit]

The formats of the partitions and the file formats differ in the individual partition types. In this section these differences are shown graphically in the form of a diagram. The partitions of a 1541, a 1571, a 1581 and a native partition are compared with each other.

Sectors per track in partition comparison[edit]

Sectors per track in the partition comparison

Directory in partition comparison[edit]

reference = https: //www.c64-wiki.de/images/7/73/Directory_im_Partitionsvergleich.png

BAM in partition comparison[edit]

reference = https: //www.c64-wiki.de/images/0/06/BAM_im_Partitionsvergleich.png

See also[edit]

Weblinks[edit]