Pseudo tape devices

Since pseudo tape devices are UNIX file names, specifying a separate UNIX file as a device provides the ability to read and write data to it at a high speed.

Such uses can be:

A copy of the ABS disks in a pseudo tape for fast reloading.
High-speed file-save backups to a UNIX file.
A serial device or network link for transmitting data to some other destination.

Note: The underscore character is a reserved character and is not valid in a pseudo tape device name.

Pseudo tape devices do not need to be compressed. For compressed pseudo tape devices, data is written compressed and read uncompressed using gzip utilities (to eliminate the 2 GB file size limitation on compressed tape devices). At user specified limits (before compression), the UNIX file name changes and cascades the pseudo tape device to the new file name.

For example, given this tape definition in the pick0 configuration file:

tape /tmp/pseudo 10000 p lx # compressed tape

If a data save has more data than the limit specified (10,000 1024 byte blocks, on 10 MB), the device /tmp/pseudo is closed and the save cascades to /tmp/pseudo-1. After the second 10 MB is written, the device /tmp/pseudo-1 is closed and the save cascades to /tmp/pseudo-2. This process continues until the save is finished.

Note: There must be space in the UNIX file system, /tmp in this example, to store these compressed files.

Changing the Compression Method

Use the !SwitchZip.sh program to change your compression method (either Compress or Gzip).

Navigate to the /usr/lib/pick directory. For example:
```
cd /usr/lib/pick
```
Run the SwitchZip.sh program. For example:
```
!SwitchZip.sh
```
The Choose compression method menu displays.
Select your compression method and press ENTER.

The compression method is changed.