IBM System/370

Access
Access mechanism
per track
Access mechanism
64 recording tracks/surface x 12
= 768 recording tracks/module
8 spare tracks/surface x 12 = 96 spare tracks/module
8 recording elements
1 spare
8 recording
elements
1 spare
216 recording
elements (read/write headsl/access mechanism x 4 = 864 recording elements
Figure 20.15.1. Top view of a 2305 Model 2 disk surface
DATA RECORDING ON THE MODEL 1
Access
mechanism
Self-formatting records are written on a Modell as on a Model 2.
However, data is recorded on the disks of a Modell module in a unique
way in order to achieve faster data access. The Modell module contains
the same number of recording elements as the Model 2, but they are
positioned in such a way as to double the data transfer rate and halve
the average access time. The capacity of the Model 1 is less than
half that of the Model 2 because (1) only 384 recording tracks and
48 spare tracks are used, (2) there are two RO records present on each
physical track (360-degree arc) of the Modell, and (3) the gaps between
data areas on a Model 1 track are larger than those of the Model 2
because of the higher data rate of the Modell.
An addressable recording track on a Model 1 occupies a 180-degree
arc on a disk surface rather than a 360-degree arc as on a Model 2.
43