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IBM DBA-ESDI Hard Drives

DASD Storage Interface Specification Micro Channel (Rev. 2.2, Sep 1991)

Systems with DBA-ESDI
Direct Bus Attachment Pinout
Edge Connector Type
   Straight Connector
   Right Angle Connector
WD387 60MB Drive PCB
160MB DBA-ESDI PCB

Systems with DBA-ESDI

A list of systems equipped with the DBA-ESDI interface:

• PS/2 Model 50 (Z) - HDD adapter/riser edge connector (some with MFM instead)
• PS/2 Model 55 SX - bus riser cable
• PS/2 Model 70 - drive riser connector
• PS/2 Model P70 - planar cable (2x berg to 1x edge)
• PS/2 Model 90 - 2x planar edge connector (pads only on later samples)
• PS/55 Model 5540 - bus riser edge connector
• PS/55 Model 5550 386 - drive riser edge connector
• PS/55 Model 5560 - 2x planar edge connector (pads only on all known samples)
• 7541/7542 Industrial Computer - HDD adapter/riser (same as 50 Z)
• 7561/7562 Industrial Computer - drive riser edge connector
• ThinkPad 700/720? (non-standard form-factor)
• Reply Model 32 - planar cable

Direct Bus Attachment Pinout

The following table shows the signal assignment and pin numbering for the 2 x 36-pin hard drive edge connector. Side A of the connector is the top (component side) and Side B is the bottom (solder side).

This is a subset of the standard 16-bit Micro Channel interface (pinouts HERE). The most notable omission is the top eight address lines, which reduces the addressing capability from 24-bit (16 MB) to 16-bit (64 KB).

Notes:
1) The signal is marked as 14.3 MHz OSC in the Model 70 technical reference and as "Reserved" in the P70 and 55 SX reference. It's not confirmed whether the signal exists in all implementations.

There is a physical key between pins 2 and 3 (A02 and A03; B02 and B03). Not all connectors have the key present.

Source:

• Model 70 (8570), 1st Ed. (May 1988) (page 38 phys.)
• Model 70 (8570), 4th Ed. (Oct 1990) (page 55 phys.)
• Model P70 (8573), 1st Ed. (Apr 1989) (page 44 phys.)
• Model 55 (8555), 1st Ed. (Feb 1989) (page 37 phys.)
• Model 55 (8555), 2nd Ed. (Oct 1990) (page 39 phys.)

Edge Connector Type

2x36-pin card edge connector, 2.54mm (0.100") pin pitch.
Through-hole; straight or right angle type.

Straight Connector

Used on the Model 50 HDD adapters, the Model 70 drive riser, as well as some PS/55 machines.

AMP 650076-1

No datasheet found so far.

Right Angle Connector

Used on the Model 90 planar (early samples only). The Japanese 5560 planar also has a provision for a pair of these connectors.

Thomas & Betts HOLMBERG A8D36RA 29C

Thomas & Betts 1992 Full-Line Catalog (physical page 191 onwards)

A8 - Series Designator; A8 - 600 V DC
D36 - Number of contact pairs and readout; D - Double Readout, 36 - # contact pairs
RA - Termination style; Right angle dip solder tails
29 - Contact plating; 29 - Standard Plating (see datasheet for details)
C - Mounting style; C - Without mounting ears

Hirose Electronics A810056101

No datasheet found so far.

WD387 60MB PCB

160MB DBA-ESDI PCB 79F6370

There are no reference designators silkscreened on the PCB.

Modifying 160MB SCSI Drive With ESDI PCB

Modifying a 160 MB SCSI Disk was only half way successful (took of the SCSI PCB and hooked up the ESDI PCB from my bad 120 MB Drive). I can see the HD when booting with the Refdisk, but I get all kinds of errors when trying to format it.

The 160 operates with a different number of sectors IIRC. Only have the data for the 80 and 160 MB: 984 cylinders, 10 heads, 17 (80) and 34 (160) sectors. So the 120 must have 26 sectors (25.5 arithmetically - but there are no half cylinders...). I think the 120MB controller cannot "fetch" a valid sector start and therefore jumps out. The LLFORMAT routine does not go *that* deep that it can write raw sectors on the media. That's usually the purpose of some factory tools.