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takes approximately one minute to complete. During
this time, four cleaning brushes sweep across the disk
recording surfaces to remove dust particles. The one
minute sequence also allows the machine electronics and
the temperature in the disk enclosure to stabilize.
At the end of the start-up sequence, the disks are
spinning at 1500 rpm with the read/write heads loaded
over the disks at track 000. A 'ready' signal indicates to
the using system that the 5444 can start operations.
Stop sequence commences when '+24V file start'
drops. The read/write heads unload and retract off the
disks. When the disks have stopped, the 5444 can be
opened to remove the disk cartridge.
Note: When '+24V file start' is dropped, all de power
supplies remain on at the machine and ac power is still
present in the ac box.
Carriage Movement
• Controlled by 'access forward' and 'access reverse'
lines from the using system.
The 5444 must be ready before a carriage movement can
begin. While the read/write heads are moving over the
tracks on the disk, the 5444 generates 'track crossing'
pulses to enable the using system to determine the head
position.
When 'access forward' or 'access reverse' is activated,
the carriage moves the heads across the disk surfaces.
When the access command is dropped, a detent
mechanism engages and stops the carriage, leaving the
read/write heads positioned over the required track.
Read/Write Operations
• Read/write operations are controlled by 'read select',
'write select', and 'erase select' lines from the using
system.
To perform a read or write operation, the appropriate
head is defined by 'head select' and 'disk select' lines.
The read or write is further defined by 'read select' or
'write select' and 'erase select' lines respectively from the
using system.
The erase coil is always energized during a write
operation to trim the edges of the written data tracks.
This technique is called 'side erase'.
1-2
(S/70)
Manual Control of the 5444
The 5444 may be controlled manually from a CE
control panel. Two switches on this panel enable the
5444 to be switched off-line to give manual selection of
any head or track. When controlled from the CE control
panel, the 5444 is write-inhibited.
Machine Control from the Using System
The 5444 is under the complete control of the using
system for accessing, reading, and writing. The 5444
contains access control logic, read/write logic, and safety
and interlock circuits. Twelve input and eight output
lines form an interface with the using system. The
interface is described in Chapter 3.
DATA ORGANIZATION
• Track format is determined by the using system.
• Where a byte is referred to, an 8-bit byte is implied.
Cylinder
The 5444 contains two disks, totalling four surfaces for
recording. (Model 3 has one disk, giving two recording
surfaces.) Each disk consists of 203 concentric cylinders.
(Model 1 consists of 103 cylinders.) Each cylinder has
two tracks, one on the top surface, and one on the
bottom surface. At each cylinder address, either track
may be read (or written onto) by selecting the
appropriate read/write head.
Alternate Cylinder Assignment
Model 1 has 103 cylinders, Models 2 and 3 have 203
cylinders. On all models, three of these cylinders are
used as alternate cylinders where data is transferred to
replace a defective cylinder. The alternate cylinders are
numbered 001, 002, 003 (on all models).
CE Cylinder
One extra cylinder on each disk (Model 1: cylinder 103;
Models 2 and 3: cylinder 203) is reserved for CE use
during maintenance.
Track Format
• Each track is divided into 24 sectors.
• An index marker pulse indicates the start of each
track.
The track format is shown in Figure 1-2. Each track is
divided into 24 equal length sectors. A data record is
identified by specifying the cylinder, head, and sector
number corresponding to that record.
An index marker pulse indicates the start of each track
and aligns all tracks on any disk. The index pulses are
derived from index transducers monitoring rotation of
the two disks. The upper removable disk and the fixed
disk have separate index transducers.
After the index pulse, there is a gap of 32 bytes before
the first sector is written. This gap allows for variation in
the position of the index pulse.
Sector Format
• Each sector contains an identifier field and a data
field.
• Address marks denote the beginning of each sector.
The sector format is shown in Figure 1-3. The beginning
of each sector is denoted by address marks which are
derived from the 'read data' output of the read
amplifier. A data separator in the using system separates
'read data' into data pulses and clock pulses. The data
separator also provides address marks indicated by
missing clock pulses.
The identifier field contains a flag byte, two address
bytes, and three check bytes. The flag byte indicates
either that the entire track is not used because of some
defect, or that the track is an alternate track replacing a
defective track. The two address bytes contain the sector
address as a 14-bit binary number. The three check bytes
are generated by the using system to verify the identifier
field.
The data field contains one synchronizing byte from
the using system, 256 data bytes, and three check bytes.
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