Help me! Before I take the plunge

[Ethan Dicks]

On Mar 31, 2005 4:27 PM, Glen Goodwin <acme at gbronline.com> wrote:
> Okay, so out of curiosity I found the listing for the Decmate on eBay: 
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=1247&item=5180062401&rd=1&ssPageName=WDVW
> 
> Now, this is a pretty cool looking critter.

Very 1980s...

> Please bear in mind that I'm essentially an 8-bit micro guy...
> However, the Decmate has a number of appealing qualities:
> 
> Small size -- will fit in my HideOut (computer room)
> "Somewhat" PDP-8 compatible -- a whole new world for me
> Affordable -- even with shipping it's within my budget
> Attractive appearance -- looks like a computer my wife can relate to
> instead of some gargantuan refugee from a '50s sci-fi movie

It is smaller and cheaper than, say, a PDP-8/e...
 
> On the other hand, I have some questions (I did a little Googling and
> have more to do, but I know there are folks here who can answer my
> questions quickly and accurately):
> 
> Is it a fair value at $200 plus (probably) another $200 for shipping?

Others have chimed in, but let me put it this way... _I_ didn't
consider a bid for it.

OTOH, if one has a number of DEC machines, one can one or both of the
RX02s in the pedestatl with, say, a PDP-11.  They are indepenent, BTW,
so one could hook one RX02 to the DECmate, and the other to a MINC-11
(same DB-25 external cable pinout).

> Is technical documentation available?

Yes, on bitsavers.  I was just reviewing the docs for it the other
day, and the schematics look complete.

> What OSes will run on it? (OS/8 ?) Are they available for download?

OS/278 has the necessary patches to deal with the differences in the
console IOT behavior that was well described in another post.  Dunno
about download, but you'd have a problem with the downloaded file,
since the RX02 format can _not_ be written by a PC FDC (it's a hybrid
format that only the RX02 drive (and DEC-compatible 3rd-party
drives/controllers) can write.

> What software, languages, assemblers, etc. are available?

Once one has OS/278 up, the list is the same as for OS/8.  Primarily,
folks wrote in FORTRAN or 12-bit MACRO, but there are a few other
languages available.

> How compatible is it with the PDP-8 -- ie, will it run PDP-8 software?

Yes, except for the aforementioned console incompatibilities.  It's
not hard to tweak stuff to work with the DECmate, but stuff that does
its own console IOTs _does_ need to be slightly tweaked.  Much easier
with the MACRO source than without.

> Does it have a free serial port so I can download software onto a PC and
> then serial-transfer it to the Decmate?

I don't remember.  If one has the communications board (DP278?), one
has the spare port for sure.  The only problem then is a
chicken-and-the-egg problem... how to get a program into memory
without already having a program that understands that protocol.  The
quickest answer (but not necessarily the easiest answer) is to get a
bootable RX02 disk with Kermit on it.

> How expandable is it?  What sort of bus does it have?

It is in-cabinet expandable only... the available options are more
serial ports (DP-278), and an external hard disk (RL278?)  I have
never personally held either option.

The bus is a proprietary one, that happens to fit on two slots
mechanically identical to, say, an Qbus.  The pinout is described in
the pdfs on bitsavers.

> What are the Decmate's disadvantages?

  Not console IOT compatible
  EAE not possible to attach.

> Is there a better machine I should hold out for which is small and in
> the same price range?

DECmate IIs and DECmate IIIs are cheaper... I don't consider them if
they are loaded with standard equipment and priced above about $40. 
It's easy to add a hard disk (ST-225, for example) to a DECmate II,
making it attractive.  The DM II and DM III also use 5.25" 'RX50'
diskettes which *can* be read/written from a Linux/Windows/etc machne.

There's also the possibility for going with an SBC6120
(http://www.sparetimegizmos.com/), but the SBC6120 is *not* cheaper
(but it is smaller and more compatible) than this DECmate I.  With
front panel and I/O board, I have several hundred dollars in my
SBC-6120, but at the moment, they are a lot rarer than even the
PDP-8/S.

-ethan