Operator Controls - IBM 1800 Operating Procedures Manual

IBM 1810 Disk Storage
The IBM 1810 Disk Storage provides random-access
storage capabilities for the 1800 system. One 1810
(model AI, A2, A3, Bl, B2 , or B3), providing up to three
disk storage drives , can be attached to the system. The
1810 operates under data channel control and functions
as both an input and output device.
The disk storage recording medium is an oxide-coate d
disk in an interchangeable 2315 Disk Cartridge (Figure 24.)
The access mechanism consists of two parallel
horizontal arms that straddle the disk. Each arm has a
magnetic read/ write head, positioned to read or write on
the corresponding disk surface. The entire assembly moves
horizontally, allowing the heads to have access to the
entire recording area (two surfaces).
Writing or reading of disk information occurs as the
disk surface revolves (at 1,500 rpm) past the read/write
heads. Information is written by magnetizing small
discrete areas in a circular pattern around the disk. In-
formation is read by sensing the presence or absence of
the magnetized spots around the circula r pattern on the
disk.
The circular patterns of data on the disk are called tracks.
The track on the upper surface of the disk and the corre-
Figure 24. 2315 Disk Cartridge
sponding track on the lower surface of the disk are called
a cylinder. The total number of cylinders is 203; three
cylinders are used as spares to ensure that 200 cylinders are
available for use.
OPERATOR CONTROLS (Figure 25)
B B
G
B B
G
B B
G
Figure 25. 1810 Keys and Lights
66
IBM 1800 Operating Procedures
CARTRIDGE
UNLOCKED
CARTRIDGE
UN LOC KE D
CARTRIDGE
UN LOC KE D
I
I 7725 BI
Each 1810 provides up to three disk storage drives.
Individual sets of controls are provided for each drive.
Each set (top, center, or bottom) controls the correspond-
ing disk drive (top, center, or bottom).
The Start Key, when pressed,
applies power to the drive
motor and initiates a cycle up (start) sequence provided
the disk cartridge is fully into position and the disk is
locked to the drive spindle. The cycle up sequence consists
of:
1. A 90-second delay while the disk is being cleaned
and coming up to speed.
2. The loading of the heads after the 90-second delay.
3. The ready light turning on indicating that the drive
is ready for use.