Although A-Shell itself can exist in any directories, for system administration purposes is may be wise to try to separate it from other application and operating system directories, if possible. This is less of an issue under Windows, where you typically have only one file system (or partition) available, and thus the best separation you can achieve is to give A-Shell its own directory tree, and possibly its own share name. Under Unix on the other hand, it is normal to have multiple file systems, and there are some particularly good reasons for defining one or more individual file systems to keep A-Shell separate from the rest of the operating system:

In essence, there are two separate sets of files which are installed: the A-Shell runtime system, consisting of the AMOS emulation command programs and the A-Shell module itself, and the development system, consisting of the object modules and source to a user-defined subroutine module, enabling subroutines to be developed. Since the second set of files is usually offered as an added-cost option, most users will only need to concern themselves with the first set.

After installation, it is necessary to install the security key that was supplied at the time of purchase. This process is described later in this section. If you don’t have a security key, the software will run in demo mode, which is fully functional except for nag messages (which will eventually drive you crazy) and the single user limitation.

If you are updating an existing A-Shell installation, you should follow the same process as for an original installation. Under all operating systems, the installation process will detect that (or ask if) an update is being performed and will not overwrite any existing configuration files. Any configuration files that might have new fields added, or differing formats, are stored in example form with .new extensions. If the function key translation tables are updated, the original ones will be saved with .ifs (.ifx) and .vus (.vux) extensions.

The ash_install script used for installing and updating A-Shell under Unix will execute two special customization scripts—pre_ash_install and post_ash_install—if they exist in the custom subdirectory of the specified target directory tree. These allow you to customize the update process, perhaps saving, renaming, or removing certain commands or files, etc. See the sample scripts included with the release for further notes and examples.

It is possible to install A-Shell several times on a single machine, in different paths, which enables entirely separate A-Shell environments. While this is generally not recommended for end-users, who are typically running A-Shell as a single-purpose application, multiple environments can be very useful for developers and resellers for a variety of purposes: development versus production systems, duplicating customers' systems, etc. The recommended directory structure is to have all virtual machines located in the \VM or /vm directory. Each A-Shell installation would live one directory level below this identified by its machine name and the MIAME environment variable pointing to this subdirectory. It is recommended that the first A-Shell installation on a machine be made in the default directory \VM\MIAME or /vm/miame.