CDC Finch Alternatives Today [WAS:RE: Evotek Winchester Harddisk]

Tom Gardner t.gardner at
Wed Dec 9 13:58:38 CST 2015

The manual u cited states, "The disk controller can control either a CDC or Finch drives. All drives attached to any controller must be of one type."  I'm not sure what they mean by "CDC" but if u are lucky it might mean "SMD."

According to the 1983 Disk/Trend Finch interfaces were available on the Wren 9415-32 (Finch and ST506) and the Wren 94153 (Finch only).  So u might look for a 94153 or a Finch variant of the 9415-32.

The Finch spec data interface specs include 13440 unformatted bytes per revolution using an 806 KB/sec  data rate, which are the very old at that time 3330 industry standards.  There are very few small drives that use this standard, not even the 94153 (10,080 @ 605 KB/sec) so what happens with the drive at a different frequency and the controller with a possibly a different number of raw bytes per track is unpredictable.   Note that 10080 x 806/605 is close enough to 13440 so any 10,080 @ 605 KB/sec drive might be made to work if the recording channel has margin at the higher frequency; unfortunately there are not very many.

A bigger problem might be the command and control interface of the Finch - it is not like the ST506/412.  Off the top of my head it looks like a variant on SMD.  BTW SMD data specs are exactly 1.5x3330, that is 20,160 bytes @ 1.209 MB/sec so a small SMD might work if the recoding channel can deal with the lower data rate, perhaps the 8715 FSD.  You might want to compare pin by pin SMD to Finch to see if this is even possible.   There were some small SMDs, e.g. Micropolis 1403, Priam 804 but most were 14-inch.

Perhaps there is a CDC SMD expert in this group that can help


-----Original Message-----
From: Oliver Lehmann [mailto:lehmann at] 
Sent: Monday, December 07, 2015 11:39 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Evotek Winchester Harddisk

Tom Gardner <t.gardner at> wrote:

> Sorry If I didn't make myself clear, I am suggesting one never acquire 
> an Evotek drive today other than perhaps as an historical curiosity.
> The Finch was a short lived 8-inch HDD that went up to 42 MB 
> unformatted BUT according to Disk/Trend It did not use an ST506 
> interface but instead came with this  variety of interfaces: Finch, 
> LDI, SMD or SA1000!  So your problem is likely to be finding a drive
> that matches the interface of yr controller card.   Some possibilities
>           Finch interface was available on certain CDC Wren 5 -inch  
> models, e.g. 9415

 From what I understood in the Zilog System 8000 manuals, it is the Finch interface.

Page 33 - Drive Performance Characterstics Page 47 - Pinout of the WDC-Controller Disk Connector Page 65-69 - Describing Driver Configurations

Here are pictures of harddisks used in the System 8000:

And this is the so called "FINCH Adapter Board" used in the S8000:

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