Determining The Amount Of Storage Available On A Tape Cartridge - IBM 5110 User Manual

78
DETERMINING THE AMOUNT OF STORAGE AVAILABLE ON A TAPE
CARTRIDGE
There are approximately 204K bytes of storage on each tape cartridge,
but the amount of tape storage actually available to you depends on:
• How many files are marked (formatted) on the tape
• How the data files were written to tape
Each file on a tape cartridge requires one 512-byte file header.
Therefore, as you mark more files on a tape cartridge, more tape
storage is used for file headers. For example, if you mark one 3K file
on a tape, 512 bytes of tape storage are used for the file header.
However, if you mark three 1 K files on tape, 1,536 bytes of tape
storage are required for the file headers.
One 3K File
IO.5K
3K
,
Three 1 K Files
I O.5K 1
1K
O.5K 1K
O.5K 1K
Notice that, in each case, a total of 3K bytes of tape storage is
allocated for tape files. However, in the second case, an additional 1 K
bytes more of tape storage are used.
The amount of data you can store in a data file depends on how the
data is written to the data file. (See Input/Output Control for a
complete description of writing data to data files.) For example, when
you first write data to a data file (an OUT operation), the individual
records are sequentially written to tape starting at the beginning of the
data file. Once these records are written to tape, the data file might
look like this:
Data File
I)
.... 1
~II--------Data
Records - - - - - - -.....
_=
~\----------/~:~/~~
Beginning of the Last Data Record Unused End of the
Data File Tape Storage Data File