User`s guide

Figure 1-7. Disk Organization
In Figure 1-7, the first N tracks are the system tracks. System tracks are required
only on the disk used by CP/M 3 during system cold start or warm start. The
contents of this region are described in Section 1.6.1. All normal CP/M 3 disk access
is directed to the data tracks which CP/M 3 uses for file storage.
The data tracks are divided into two regions: a directory area and a data area. The
directory area defines the files that exist on the drive and identifies the data space
that belongs to each file. The data area contains the file data defined by the directory.
If the drive has adequate storage, a CP/M 3 file can be as large as 32 megabytes.
The directory area is subdivided into sixteen logically independent directories. These
directories are identified by user numbers 0 through 15. During system operation,
CP/M 3 runs with the user number set to a single value. The user number can be
changed at the console with the USER command. A transient program can change
the user number by calling a BDOS function.
The user number specifies the currently active directories for all the drives on the
svstem. For example, a PIP command to copy a file from one disk to another gives
t@e destination file the same user number as the source file unless the PIP command
is modified by the [G] option.
1-12
1.4 Region Boundaries CP/M 3 Programmer's Guide