Centaur Close-ups

Readers have expressed interest in seeing what exactly a Western Digital ‘Centaur’ drive looked like. I took a few photos of a WD95044-A drive, the larger capacity (40 MB) and newer variant of the WD Centaur family. Some photos were taken with the PCB removed in order to show what the chips on the PCB look like and what the drive chassis looks like without the PCB covering it.

Here’s what the drive looks like:

A late 1990 WD Centaur model WD95044-A

Its tank-like appearance is nothing like WD’s very modern Caviar drives. The Centaur looks like a mid-1980s drive, not something made at the end of 1990.

WD950440-A drive lid

The top of the drive shows an old-school defect table, but with no defects listed. It’s not clear if that just means this particular drive had no defects or if the drive’s IDE controller remapped them; either is plausible.

Here’s what the bottom of the drive looks like with the PCB removed:

WD90544-A drive bottom with PCB removed

The black box of the stepper motor is clearly visible in the upper left. The big Nidec spindle motor stands out, and it is quite large, adding to the drive’s height.

Here are two further images of the bottom side of the drive shot from different angles:

Centaur bottom from an angle
And a different angle

The chassis is very “3D”, not at all flat. This is a half-height drive, wasting a lot of space for only 40 MB of storage.

Western Digital cared to put its name even where customers where unlikely to ever see it:

Cast in WD’s image

Here’s a detail of what I believe is a sensor that detects the “index hole”, which lets the drive measure its RPM and also determine the start of a track. There is an indentation in the side of the spindle motor housing. I believe that when the indentation passes under the sensor, it will trigger a pulse that serves the same purpose as an index hole on a floppy.

Spindle rotation sensor

Here’s one side of the drive, with the stepper motor on the left. The drive has a very “mechanical” look, with lots of screws and bolts and stamped and cast metal. It does not look neat.

Stepper side of the drive

Here’s the other side of the drive. There isn’t really much to see:

Boring side of the drive

And now the connector side. As was common with old IDE drives, there is no shroud around the IDE connector but there is a key pin. This drive is jumpered as a slave, with the jumper in the middle position. Note that the Molex style power connector is in the usual position but upside down. Fortunately it has a shroud that makes plugging the power connector backwards reasonably difficult.

Centaur connectors

Here’s the PCB; this is the boring bottom side that is visible when it’s mounted on the drive.

PCB bottom

And here’s the much more interesting view of the top side of the PCB which has all the chips on it:

PCB top, with all the good stuff visible

Not surprisingly, the core chips are almost all Western Digital’s own. The big WD42C22A ‘Venus’ is the same chip WD used on their ESDI/RLL/MFM controllers in the late 1980s and early 1990s. The larger chip next to it has a WD part number and (C)WDC ’90 but also (M)(C)i ’80, suggesting that it’s an Intel microcontroller with WD firmware in its ROM.

The smaller WD chips are WD10C22B, a self-adjusting data separator (supports MFM and RLL encoding), and WD12C20, for which I could find no documentation.

The Philips FCB61C65L-70T chip is an 8Kx8 SRAM with 70ns access time.

Here’s a better view of the connectors on the PCB:

Centaur PCB connectors

The leftmost white connector visible in the photo above is attached to the stepper motor, the small two-pin connector in the middle to the RPM sensor. The largest connector goes to the spindle motor. There is another 12-pin Berg/DuPont style connector, not visible on the photo above, that links the PCB with the read/write heads.

Here’s the stepper motor:

WD95044-A stepper motor

Here’s one more view of the stepper motor. It says: WARNING REMOVAL OF THIS COVER WILL VOID ANY AND ALL WARRANTIES. I guess they really didn’t think the cover was safe to remove.

Really, don’t take that cover off!

Amazingly, even though the WD95044-A is painfully slow with 28ms average seek time quoted by the manufacturer (just seek time, not access time!), it is much faster than its predecessor, WD95048-A with absolutely glacial 69ms average seek time.

This entry was posted in PC hardware, PC history, Storage, Western Digital. Bookmark the permalink.

3 Responses to Centaur Close-ups

  1. Michal Necasek says:

    Yes, those I found. Unfortunately I had a typo in the article (now fixed); the drive has a WD12C20 chip on it, not WD10C20, and I clearly got lost in the alphabet soup. The WD10C20 appears to be a predecessor of the WD10C22.

  2. Octocontrabass says:

    Hmm, what do we have here…

    HA13441WD – spindle motor driver
    UC3770A (x2) – stepper motor driver
    32P541 – read amplifier
    WD10C22B – data separator
    WD42C22A – single-chip MFM/RLL/ESDI/IDE controller with DMA support
    FCB61C65L – 8kB (16 sector?) buffer RAM
    62-602050-101 – Intel microcontroller (8051?) with probably OTP ROM

    That leaves only the WD12C20, which doesn’t seem to have any public datasheets, and the 186086-001 and 186622-001, which could be just about anything because Micro Linear made a lot of custom parts.

    Huh, the spindle motor has the part number 186001-002 on it. I wonder why it’s so similar.

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