【Fujitsu】 FACOM 477A Disk Pack Unit

The FACOM 477A was a grouped disk pack unit from Fujitsu equipped first with a command retry function and ECC function. It was completed in 1972.

The FACOM 477A disk pack unit was developed by making dramatic performance improvements to the previous FACOM 472L-- namely, increasing memory capacity, reducing access time and increasing data transfer speed. Furthermore, the following new functions were developed using the FACOM 1771A and FACOM 1771B disk pack controllers for controlling the FACOM 477A.

1) Multiple-request function using a rotation position detection mechanism
2) Command retry function
3) ECC function
4) Maintenance and diagnostic functions

The FACOM 1771A/B-FACOM 477A subsystems were connected to the block multiplexer channel (BMC) of the host system. These functions became the basis of technology for realizing later high-performance and high-reliability disk subsystems.

In 1975 Fujitsu developed the FACOM 478A2 disk pack subsystem based on these technologies. This subsystem maintained performance and reliability while dramatically improving cost performance. The FACOM 478A2 used a structure where two drives were arranged horizontally in the cabinet, thereby eliminating the need for the automatic pull-out mechanism required for vertical dual structures like those in the FACOM 477A. This made it possible to realize both economy and reliability, and achieve miniaturization and lighter weight. The grouped type was used with the previous 477A, but the individual cabinet system was used for the FACOM 478A2 and subsequent models to facilitate expansion.

In 1976 Fujitsu completed the FACOM 479B2 which improved track density from the previous 192TPI to 370TPI, and expanded memory capacity of each pack to 200Mbyte.

There were two implementations of the disk media and the access head. One was the replaceable type which was used with the FACOM 477/478/479, and another was the non-replaceable type which incorporated the disk media and the head into an all-in-one unit. But later magnetic disks for large general-purpose computers switched to non-replaceable type only, and the FACOM 479B2 became the final replaceable disk pack unit.

Specifications of FACOM 477A/478A2/479B2 Disk Pack Units
  (Reference)
FACOM 472L
FACOM
477A
FACOM
478A2
FACOM
479B2
Completion date 1971 December 1973 October 1974 August 1975
Equipment type Grouped Individual
Memory
capa
-city
Track
capacity
7,294byte 13,030byte
Pack
capacity
58Mbyte 100Mbyte 200Mbyte
Unit 116Mbyte 200Mbyte 400Mbyte
Subsystem 466Mbyte
(8spindles)
800Mbyte(8spindles)/
1600Mbyte(16spindles)
12.8Gbyte
(64spindles)
Disk
pack
Number of tracks/
cylinder
40 19
Number of cylinders/
pack
200+3(spare) 404+7(spare) 808+7(spare)
Number of tracks/disk side 406 411 815
Number of disks 13 12
Effective number of sides 20+1(servo) 19+1(servo)
Diameter 17inch(430mm) 14inch(356mm)
Positioning time Average 50ms
(Min. 15 ms,Max. 80 ms)
Average 25ms
(Min. 6ms,Max. 45ms)
Rotation speed 2,400rpm 3,600rpm
Average
rotational delay
12.5ms 8.4ms
Data transfer speed 312Kbyte/s 806Kbyte/s
Recor
-ding
density
Linear
density
2,200BPI 4,040BPI
Track density 127TPI 192TPI 370TPI
Main connected
systems
*1

*1:·Fixed length type: FACOM 230-35
·Variable length type: FACOM 230-45S/55, FACOM 230-60, FACOM 230-75


FACOM 477A Disk Pack Unit Had 100Mbyte memory capacityFACOM 478A2 Disk Pack UnitFACOM 478B2/479B2 Disk Pack UnitThe photo shows the FACOM 478B2 connected to the FACOM 230-38 system. The small cabinet on the near right side is the disk pack adapter.