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itstar is a tool for extracting files from ITS backup tape images. This tool is used with the Tapes of Tech Square ToTS collection to extract files.

Background

Tapes are structured into "files", and the files are divided into "records".  The .tap files preserve this structure with some metadata, which encode the size for each record.

Each record is stored like this inside the .tap file:

   <record size, four bytes>

   <data, "size" number of bytes>

   <record size again, four bytes>

A tape "file" is a series of records, ending with an "tape mark".  The mark is encoded as an empty record, which is just <record size = 0>.

After this comes the next file.  A tape is ended with two consequtive tape marks.  (BUT! this is just a sofware convention; there may be more data after this.)

Note, a "tape file" doesn't have to correspond to the files we see stored on the tape.  An operating system or backup software can read and write tape files and records any way it sees fit.  For example, a tape could be a single "tape file" but store several "software files".  Or it could be many "tape files" but store a single "sofware file".  ITS does store its "sofware files" as "tape files", with records limited to 1024 36-bit words, which are either 5120 (9-track) or 6144 (7-track) bytes.

Running the tool

1. Open up the terminal in BitCurator 

2. Navigate to the folder where you want the extracted files to end upcontaining the itstar program
   

3. Construct the command you'll use to extract the files.
   

   1. The first time(s) we run the command we will use the "t" option to only print to the terminal what files would be extracted by the command. This will help when determining the other options to use.

   2. "f" incidates we are using a tape image file, not reading from a tape itself.

   3. The .tap files are not all encoded the same way, and there's no telling how a particular file is encoded except either 1) look at the byte codes inside, or 2) trial and error.  We will use trial and error first (with the "t" option passed for print only).

      1. -E is for using the E-11 tape image format or even-sized tape records

      2. Big or little endian record size. Detault is little, pass -B for big.

      3. 9 or 7 track tapes.  9-track stores eight bits per byte.  7-track store 6 bits plus parity.  Default is 9, pass -7 for the latter.

      4. Two of the most common are "-7B": 7-track tape with big endian record sizes. Or just -E for 9-track little endian with an even-sized tape record.
          

         Code Block
         language bash
         # Basic elements of the command $ itstar -t[tape encoding options] -C /path/where/you/want/the/extracted/files/to/go -f /path/to/tape/image.tap # Example of 7-track tape with big endian record sizes # 9-track little endian with an even-sized tape record