Cheapest DOM for the JrIDE?

Hardware questions and modifications

Cheapest DOM for the JrIDE?

Postby Tempest » Wed Feb 25, 2015 8:34 am

What's the cheapest DOM I can buy that works with the JrIDE? I've currently using a 2GB IDE hard drive, but it's annoying to have to have the huge enclosure on my desk. I know you can get 8GB DOM modules for $35 or so, but that seems like a waste since I've barely filled up even a small fraction of my 2GB hard drive.

Would this 2GB DOM work or does it have to be 8GB or greater? http://www.amazon.com/Kingspec-KingSpec ... 009FX95C2/

Or this cheap one on ebay: http://www.ebay.com/itm/Kingspec-44PIN- ... 1786112081
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Re: Cheapest DOM for the JrIDE?

Postby James » Wed Feb 25, 2015 1:12 pm

I am using a 128 MB DOM and a 32 MB DOM so smaller DOMs work. I want to upgrade to a 512MB eventually. I think they go for about $15
-PCjr (1989)-DOS 3.3, Racore Drive II, jrIDE-128 MB DOM, jrExcellerator, Tandy Mod, Serial Card, Combo v2, Config Plus, IBM Parallel Port, Megaboard, Xircom PE3-10BT
-PCjr (2001)-DOS 3.3, jrIDE-128 MB DOM, NEC v20, Parallel Port, Comswap, Xircom PE3-10BT
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Re: Cheapest DOM for the JrIDE?

Postby Tempest » Wed Feb 25, 2015 1:32 pm

512MB is probably all I need considering most games that will run on the PCjr aren't that large.
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Re: Cheapest DOM for the JrIDE?

Postby Trixter » Wed Feb 25, 2015 1:56 pm

I went with an 8GB DOM for about $25 because the smaller DOMs weren't that much cheaper. Also, a quick informal check of most observed commercial and shareware games made from 1981-1989 shows that, uncompressed, they take up a little over 1GB, so I thought at least 1G was warranted.
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Re: Cheapest DOM for the JrIDE?

Postby Tempest » Fri Feb 27, 2015 8:00 am

So do I want a 40 pin DOM or 44 pin?
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Re: Cheapest DOM for the JrIDE?

Postby GHiero » Fri Feb 27, 2015 8:03 am

Tempest wrote:So do I want a 40 pin DOM or 44 pin?


40 pin. Many DOMs use pin 20 as a +5v rail, but many IDE ports do not have this pin present on the header. They also have some other kind of power connector. jrIDE supports +5v on pin 20.
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Re: Cheapest DOM for the JrIDE?

Postby Tempest » Fri Feb 27, 2015 10:08 am

That's what I thought. So if a DOM comes with the power plug I can just ignore it since the jrIDE provides the power already?

Also dumb question: How can I plug a DOM into my PC? I have an adapter that lets me plug an IDE hard drive into my USB port so I can get all the data off my old hard drive, but I then need to transfer it to the new DOM. Does the DOM work just like an IDE hard drive on any PC?

Also, I'm using DOS 3.3 which has a max partition size of 32MB. Should I switch over to DOS 4 or 5 for 2GB partitions or do those have problems on PCjrs?
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Re: Cheapest DOM for the JrIDE?

Postby alanh » Fri Feb 27, 2015 10:28 am

DoM work like any IDE hard disk.

My only caution on 2GB partitions on the JR (need later DOS versions) is it takes quite a long time to do that first DIR since it has to compute the total space available on all free clusters. Takes a while. And I can't imagine ever needing more than a couple hundred meg on a JR.
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Re: Cheapest DOM for the JrIDE?

Postby Tempest » Fri Feb 27, 2015 10:31 am

I hear Compaq DOS ver. 3.31 will handle larger partitions. A 2GB would be ridiculous, but a few 100MB partitions wouldn't be a bad idea.

Is there a way to get rid of that annoying pause? Even with my current 32MB partition setup it still takes a bit to calculate the free space when I DIR.


This is what I plan on using to plug my DOM into my PC. http://www.multiprojekt.pl/ftp/weintek/ ... 12_eng.pdf
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Re: Cheapest DOM for the JrIDE?

Postby Trixter » Fri Feb 27, 2015 10:54 am

Is there a way to get rid of that annoying pause? Even with my current 32MB partition setup it still takes a bit to calculate the free space when I DIR.


The only way to get rid of it is to use DOS 3.30 or lower. You can mitigate it, however: explanation is at http://www.vintage-computer.com/vcforum ... post305997 . The basic idea is to choose partition sizes carefully by minimizing the number of clusters in the filesystem; slightly more detailed examples here: http://www.vintage-computer.com/vcforum ... post306174

Unfortunately the PCjr suffers from this worse than others because the DOS data structures are always in the slow lower 128KB. On an XT DOS filesystem using near the maximum (64K) # of cluster entries, initial DIR takes between 12-17 seconds. On PCjr, it takes at least 50 seconds :-( My AUTOEXEC.BAT has a "DIR C:" just to get the delay out of the way right after bootup.

I can't imagine ever needing more than a couple hundred meg on a JR.


I'm working on a project that will use, legitimately, almost a gig... when that's done in several months, I'll announce it here.
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