RETRO The Spectrum User Manual page 42

Chapter 9
The tape position indicator shown on the right hand side of the screen shows the
current play position, which has a slightly different meaning depending on the type of
cassette tape file being used:
1) TZX and PZX cassette tape files usually have navigate-point markers at the start
of each sequence of blocks that make up a complete program. The cassette
tape navigation will allow you to move forwards and backwards between these
navigation points, and therefore the starting points of each loadable program.
The tape position indicates which program the playback is currently within, along
with the percentage of the program has been loaded so far:
current program . percentage-complete / total number of programs
TZX and PZX cassette tape files load in real time (which can be accelerated)
so the tape navigation will show the percentage-complete increasing as loading
proceeds. For example, the screenshot shown at the start of this chapter shows
Manic Miner loading, with the tape navigation indicating that it is 72% of the way
through the first program, from a total of one program.
A vast majority of cassette tape files only contain a single program, even if it is
multi-chunk, so the tape navigation will show the total number of programs as one.
2) TAP cassette tape files differ from TZX and PZX files in that they do not contain
navigate-points, so there is no way to navigate from the start of one program
to the start of another. Instead, TAP file navigation is done at the block level,
where blocks usually come in pairs, with the first block describing the contents
of the second. The tape position indicates which block the playback is currently
within, along with a percentage showing how much of a block has been loaded,
followed by the total number of blocks in the cassette tape file:
current tape block . percentage-complete / total number of blocks
The blocks in a TAP file will load almost instantaneously, so the percentage
complete indication for a block will usually be at zero, indicating that the playback
position is at the start of the block. The exception is where the tape position has
reached the very end of the TAP cassette file, in which case the percentage will
show 99% indicating the end of the last block.
Some multi-load games will require you to start and stop the cassette tape when
prompted, or rewind back to the beginning. It would be unusual for a program to request
that the user rewinds or forwards to a specific point on the cassette.
Usually the tape playback position will not increase unless a program is actively trying
to load data from the cassette tape file, so you may not need to stop and start the
cassette tape file playback through the navigation controls.
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