DF32 and DS32 Drive Information

The DF32 Disk File and Control is a fixed head hard drive with a total capacity of 32K 12 bit words.  It can have up to 3 DS32 Extender Disks slaved off of it for a total system capacity of 131,072 words.  This was normally used with the earlier machines, the PDP-8, PDP-8/S, or PDP-8/I.  All the units I have are made with the older R series logic which is a diode transistor logic (DTL) made with discrete diodes and transistors. The later units were made with the standard TTL IC M series logic for use with positive bus PDP-8/I's.

The DF32 was attached to the computer through the  3-cycle data break interface via 11 to 13 cables. The 3-cycle data break was a type of direct memory access (DMA). The processor wrote to various registers in the DF32 to setup the transfer then the unit transferred the data while the processor was able to do other things.   The 3-cycles used were to increment the word count memory location in PDP-8 memory,fetch and increment the current address memory location, and then read/write the word from the peripheral to the memory location specified by the current address. When the word count reached zero word count overflow signal was generated to let the peripheral know that all words have been transferred. This method saved logic in the peripheral since the memory address and word count stored in the PDP-8 memory would take twelve cards to store in the peripheral.

The drive hardware did not organize the disk into fixed size sectors, each word on the disk was capable of being read or written independently with a maximum of 4096 words in one transfer.

DF32/DS32 Drive Specifications
Data Transfer Rate 66 microsecond per word
Average Access Time 16.67 millisecond
Data Tracks 16
Control Tracks 4
Words per track 2048
Recording Method Non-Return to Zero Inhibit (NRZI).
Flux transition represents a 1
Density 1100 bpi
Recording Media Nickel-cobalt plated aluminum disk 10"x1/4"
Operating Environment Maximum: 32 to 130 F
Recommended: 70 to 85 F
Relative Humidity: 20 to 80 %
Heat Dissipation 500 Watts
Weight 50 pounds

The DF32A/DS32A which operated off of 50 Hz power rotated slower so data transfer was 80 microseconds and average access time was 20 milliseconds.  Since the heads land on the disk when the power is removed it was recommended to not power down the drive motor any more than absolutely necessary.

Documents related to DF32 and DS32

Recently (2012) I attempted to restore another DF32 that came with my straight 8. First step was to clean. See the straight 8 restoration for my cleaning methods. On the previous drive when I removing the platter to clean it the head/track alignment seemed to get a little off making recovery of the contents on drive difficult. For this one I tried cleaning the platter installed on this drive. I put alcohol pads between the heads and the platter and then rotated the platter and then pulled the pads out to clean the heads. The platter on the top had corrosion dots where the aluminum platter corroded and pushed up the plating. The bottom seemed to have some also since it pulled on the alcohol pads when the disk was turned. After a couple turns it seemed to knock loose most of the material that was pulling on the pads. I replaced the foam seal around the covers with weatherstripping from the hardware store. I hooked up the scope to the read amplifiers and spun up the drive. There was some noise from the platter damage but it didn't seem like anything really bad was happening so I continued. One of the W532's was bad so I swapped in another W532 until I can repair it. I did manage to capture most of the data using my scope as shown in the pictures and directory listing below. The disk platter has too much corrosion to be usable though. The disk contained an earlier version of Disk Monitor System than the paper tapes I have.



PIP .SYS (0) 0025
EDIT.SYS (0) 0015
LOAD.SYS (0) 0003
.CD..SYS (0) 0006
NEW .ASCII   0000
TEM .ASCII   0000
T6  .ASCII   0000
Nothing on the drive was worthwhile enough to spend more effort trying to recover the spots where the signal had dropouts. It may be possible to have the platter re-plated or a new one manufactured but I suspect the cost would be significant. I am using the drive with my DS32 emulator board for now.

The following picture links also have descriptions of what is shown in the pictures.

Thumbnail Picture Selector

Current size small. Select picture size for links below   Small  Medium  Large

Front view ( 66K)  Back view ( 62K)  right view ( 42K)  left view ( 43K)  bottom view ( 36K)
Disk platter ( 49K)  Disk cover ( 44K)
Card area ( 58K)  Card area cables unplugged ( 54K)
Closeup of wirewrap backplane ( 85K)  Top view of cards ( 63K)
Heads ( 49K)  Head top closeup ( 50K)  Head front closeup ( 31K)
Black flat coax external bus cable ( 37K)  Shielded Mylar external bus cable ( 26K)

DF32 with Straight 8
Modified W103 ( 48K)  Modified W103 schematic ( 46K)
Bad Platter ( 59K)  Timing track A (3.9K)  Timing track A dropout (5.0K)  Data track 0 (4.2K)  Data track 0 dropout ( 28K)

Boards Used
QuantityBoard TypeDescription
G083 Disc Preamplifier  
G284 Disc Writer  
G285 Series Switch Part of head select 
G286 Center Tap Selector Part of head select 
R002 Diode Network  
R107 Inverter  
R111 Expandable NAND/NOR gate  
R113 NAND/NOR Gate  
R123 Input Bus Gate  
R202 Dual Flip Flop  
R203 Triple Flip Flop  
15 R205 Dual Flip Flop Disk address and data registers 
R302 Dual Delay (One Shot)  
R303 Integrating One Shot Start of track detection 
R602 Dual Pulse Amplifier  
R603 Triple Pulse Amplifier  
W005 Clamped Load  
W023A Head data cable 
W033A Head select cable 
W103 PDP-8 Device Selector  
W532 Dual AC-Coupled Difference Amplifiers  
W533 Dual Rectifying Slicer Convert head output to digital signal 
W990 Bare Board  

Feel free to contact me, David Gesswein djg@pdp8online.com with any questions, comments on the web site, or if you have related equipment, documentation, software etc. you are willing to part with.  I am interested in anything PDP-8 related, computers, peripherals used with them, DEC or third party, or documentation. 

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