Hardware manual

Device Diablo 31 Diablo 44
Number of drives/Alto 1 or 2 1
Number of packs 1 removable 1 removable
1 fixed
Number of cylinders 203 406
Tracks/cylinder/pack 2 2
Sectors/track 12 12
Words/sector 2 header same
8 label
256 data
Data words/track 3072 3072
Sectors/pack 4872 9744
Rotation time 40 25 ms
Seek time (approx.) 15+8.6*sqrt(dt) 8+3*sqrt(dt) ms
min-avg-max 15-70-135 8-30-68 ms
Average access 80 32 (both packs) ms
to 1 megabyte
Transfer rates:
peak-avg 1.6-1.22 2.5-1.9 MHz
peak-avg 10.2-13 6.7-8 us-word
per sector 3.3 2.1 ms
for full display .46 .27 sec
for big memory 1.03 .6 sec
whole drive 19.3 44 (both packs) sec
Table 2.2: Properties of Alto disks
Alto Operating System May 5, 1980 31
For Xerox Internal Use Only -- December 15, 1980