Seagate STT20000A, Product Manual

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Theory of operations Chapter 7
STT20000A Product Manual Page 73
The microprocessor directs all functions performed by the control logic. The
instructions are read from a flash EEPROM, which can be updated with new
firmware through a specially written tape cartridge.
The 512-Kbyte DRAM data buffer allows the drive to maintain streaming when the
host cannot provide data continuously at the tape streaming rate.
The write driver receives data from the write formatter and generates write current,
causing data to be written on tape by the tape head.
The read channel amplifies and conditions the signal from the tape head and passes
it back to the read formatter.
The head stepper and drive motor both receive current from the control logic to
control the stepping of the head from track to track and to move the tape forward
and back across the tape head.
Head design
The recording/playback head is a state-of-the art, thin-film design—a thin-film
inductive write head paired with an advanced magneto-resistive read head. This
head design provides the drive with exceptional performance and reliability. The
material composition of the head also results in exceptional wear characteristics,
resulting in stable performance throughout the life of the drive.
Flash EEPROM
Because the drive uses flash EEPROM (electronically erasable, programmable
read-only memory), the drive firmware can be easily upgraded when new revisions
of the firmware are released. The circuitry includes 128 Kbyte of flash EEPROM.
You can load new firmware by using a specially encoded firmware upgrade
cartridge. Refer to chapter 4 for information about loading new firmware using a
Seagate firmware upgrade cartridge.
Sensors and switches
A number of mechanical and optical sensors and switches are integrated in the drive
design. The Cartridge In switch detects when a cartridge is fully loaded and
positioned against the A-plane datum of the cartridge. The Unsafe switch senses
the position of the SAFE indicator on the cartridge and disables writing of write-
protected (SAFE) cartridges.
The Head-Position Sensor is an electro-optical assembly (LED and photo-transistor)
to determine the approximate head position.
The drive has an electro-optical sensor assembly comprised of a solid-state light
source (LED) and a photo-sensor (photo-transistor) that sense the beginning-of-tape
(BOT), end-of-tape (EOT), load point, and early warning holes of the cartridge.