IBM B-Series, Maintenance Information

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A New Cartridge and Tape Movement Technology
The 3570 introduces a new concept for IBM tape drives that increases reliability along with faster data
access. The 3570 drive, a key component of the 3570 Tape Subsystem, uses a new cartridge with a
supply spool and a take-up spool. The normal start point for the 3570 tape is the physical mid point of the
tape's length. As a result, to access data after the cartridge is loaded and has reached load point, the
maximum distance it must travel is 1/2 the length of the tape, and the average distance is only 1/4 the
length of tape. This reduced travel shortens data retrieval time and reduces head wear. Delays needed for
tape load threading by other tape products is eliminated since the 3570 tape cartridge never needs to be
threaded. When stationed at load point, which is near the center of the tape, the 3570 is ready to read or
write data immediately in either direction.
Interleaved Longitudinal Recording Technology
The 3570 Tape Subsystem reads and writes in a new 128-track format using the serpentine interleaved
longitudinal recording technology, first introduced with the IBM 3590 High Performance Magnetic Tape
Subsystem. All 3570 Bxx Models read and write 4 tracks at a time.
Writing and reading, with this improved methodology, along with beginning in the center of the tape, allows
high speed data access at a very low cost.
The interleaved longitudinal recording technology allows the 3570 to write multiple tracks from the center
of the physical tape to the end, in either direction, then index the head, or move the head vertically, for the
return trip. The result is tracks interleaved across the width of the tape, from the center out in both
directions.
The 3570 tape cartridge have a smaller profile than most other IBM tape products, and can not be
interchanged with other products.
Historical Comparison of Tape Technologies
See Figure 18 on page INTRO-5 for an explanation of the historical changes that have led to this new
technology.
Historically, the 18 tracks recorded on 3480 media were used to record ECC information along with the
data. The original base 3490 models also used the same 18-track format but were later enhanced in the
3490E models, which implemented two sets of 18 tracks. In the 3490E device the first 18 tracks are
recorded when the tape moves in a forward direction until the physical end of the tape is reached. Then,
using an electronic head switch (not physically moving the head itself in any direction but switching to a
second set of read-write heads), a second set of 18 tracks is recorded when the tape moves in a
backward direction until the physical beginning of the tape is reached.
In the 3590 a second generation of thin film magneto resistive (MR) heads is used, which, together with
the 3590 tape medium allows recording with much higher area density, both in number of bits as well as
number of tracks per inch. Similar to the 3590, the 3570 data is written in blocks of user data using
multiple track format and where ECC information are recorded differently compared to the older track
formats. The first set of four tracks is written from the halfway point along the length of the tape to near
the end of the tape, where the head is indexed to the next set of four tracks for return to the tape center.
The process continues until all 128 tracks are written. The process is repeated in the other direction of
tape until the tape is full.
Note: Not all tape cartridges will be full from one end to the other. This example is used to show how a
complete tape cartridge could be utilized for maximum effectiveness.
INTRO-4
IBM 3570 MI