How SAS Determines Device Types

A fileref has a device type of either MVS or HFS, where HFS identifies files that are stored in a UFS file system. The device type determines how SAS accesses the file. This device type is sometimes referred to as an access method.

If a physical name does not contain a slash (/) or a tilde (~) character to identify it as an HFS filename, then SAS uses the following algorithm to determine the device type:

Use the access method from the allocation statement, if provided, as in:
```
FILE 'example' HFS;
```
or
```
FILENAME XXX HFS 'example';
```
If the access method is not specified or is MVS, use the MVS access method.
Use the access method specified by the MVS: or HFS: prefix in the physical filename, if one is provided, as in:
```
FILENAME XXX 'HFS:first';
FILENAME XXX 'MVS:first';
```
Use the HFS access method if a slash character ( / ) or tilde character (~) appears in the physical filename, as in:
```
FILENAME XXX '~/first';
```
Use the access method specified by the FILESYSTEM= system option. See FILESYSTEM= System Option: z/OS.