Technical Reference

Appendix N

N.1   DOUBLE SIDED DISKETTES

Release 2.2 of the CP/M-86 operating system can use double-sided floppy drives. If you are using a machine with double-sided drives, you can create diskettes which have roughly twice the storage capacity that was possible with earlier releases of the operating system.

A Word of Caution about using Double-sided Diskettes

The great advantage in using double-sided diskettes is that the amount of data stored on the diskette is almost twice that of a standard single-sided diskette: 1.2 megabytes compared to 610 kilobytes. A single-sided diskette can be used on a computer with either single-or double-sided drives. However, once a diskette is formatted as double-sided NONE of the data on it can be accessed by a computer which has single-sided drives.

If you have a computer which has double-sided drives, you may not want to convert all of your diskettes into double-sided diskettes right away, since a majority of the computers currently in use are only single-sided and you will not be able to use your diskettes on them.

Creating a Double-sided Diskette

You can only create a double-sided diskette on a computer which has double-sided floppy drives. To create a double-sided diskette, you need to use version 2.8 of the FORMAT program. If your computer has double-sided drives, the FORMAT program asks the following question on the 25th line of the screen:

Format both sides of the diskette (y/n) ?

If you answer by typing a 'Y' the program creates a double-sided diskette. If you answer with a 'N' just the first side of the diskette is formatted and you have a single-sided diskette which can be used on both single- and double-sided machines.

Remember that you can only create double-sided diskettes on a computer with double-sided floppy drives, having created the double-sided diskette you can copy the operating system across using either BOOTCOPY (CP/M-86) or SYSCOPY (MS-DOS).

Copying a Double-sided Diskette

To make a copy of a double-sided diskette, you must use Version 2.5 or later, of the DCOPY program. You do not have to tell the DCOPY program whether or not the diskette to be copied is double- sided: the program automatically knows. To copy a double-sided diskette, you must have double-sided drives in your computer. If you try to DCOPY a double-sided diskette on a computer which has only single-sided drives, DCOPY prints an error message and aborts the copy.

Converting Single- and Double-sided Diskettes

If you have a computer that has double-sided floppy drives, you may want to convert some of your single-sided diskettes into double-sided diskettes (see the caution above). To do this, create a double-sided diskette by using the FORMAT program as described above. Then use PIP (CPM/86) or COPY (MS-DOS) to copy the desired files from the single-sided diskette to the double- sided diskette you just created.

At times you may need to convert a double-sided diskette back into a single-sided diskette. Using the FORMAT program create a single-sided diskette. Then use PIP (CPM/86) or COPY (MS-DOS) to copy the desired files from the double-sided diskette to the single-sided diskette. You may need two or more diskettes to hold all of the data from a double-sided diskette.

Diskette LED's

The LED associated with each diskette is lit during diskette I/O. Specifically, it is lit at the initiation of a read or write and remains lit for approximately 1/2 second after the I/O is completed. The LED also stays lit as long as there is a "dirty buffer" in RAM since this is considered as being "in the middle" of a write operation.

This implementation permits the following simple rule for end users: "do not remove the diskette when the LED is lit."

If a diskette is removed while there is a "dirty buffer" in RAM, the drive is marked Read Only (R/O). This prevents destroying disc data in case the diskette is replaced by another diskette.

Diskette Label

Track 0 of each disc has a label which contains information relating to the structure of the diskette (such as location of the directory).

Prior to the 2.0 release space was reserved for the label, but the label was not used by the system.

With release 2.0, two types of diskette may exist. One type contains boot tracks, starting with track 1, with the directory and data following. The other type has the directory and data starting at track 1.

N.2 Boot Disc Label Format 


Track 0 Sector 0

Byte
Offset         Name                Description

0              System disc ID      literally, ff,00h for a system 
                                   disc

2              Load address        paragraph   to   load   booted 
                                   program at. If zero then  boot 
                                   loads in high memory.

4              Length              paragraph count to load.

6              Entry offset        I.P.  value  for  transfer  of 
                                   control.

8              Entry segment       C.S.  value  for  transfer  of 
                                   control.

10             I.D.                disc identifier.

18             Part number         system identifier  - displayed 
                                   by early versions of boot.

26             Sector size         byte count for sectors.

28             Data start          first   data  sector  on  disc 
                                   (absolute sectors).

30             Boot start          first   absolute   sector   of 
                                   program  for boot to  load  at 
                                   'load  address'  for  'length' 
                                   paragraphs.

32             Flags               indicators:
                                        bit  meaning
                                       15-12 interleave    factor 
                                             (0-15)
                                         0   0=single sided
                                             1=double sided

34             Disc type           00 = CP/M
                                   01 = MS-DOS

35             Reserved

38             Speed table         information  for speed control 
                                   proc.

56             Zone table          high track for each zone.

71             Sector/track        sectors  per  track  for  each 
                                   zone.


















Last revision 29/01/2005