Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!rice!uw-beaver!ubc-cs!jalbert
From: jalbert@cs.ubc.ca (Francois Jalbert)
Newsgroups: comp.sys.ibm.pc
Subject: Extended Memory Board
Summary: Looking for such boards
Keywords: Extended Memory Board
Message-ID: <6169@ubc-cs.UUCP>
Date: 5 Jan 90 05:06:02 GMT
Sender: news@cs.ubc.ca
Reply-To: jalbert@cs.ubc.ca (Francois Jalbert)
Organization: UBC Department of Computer Science, Vancouver, B.C., Canada
Lines: 88

Hello everybody. I have been looking for a while without success for 
the following:

   4 Mb of extended-only memory starting at 1384 Kb in memory space.

So far, none of the dealers I talked to knows anything about such
boards. They looked into their books and found nothing appropriate.
If I can supply them with a maker and model number, they claim that
they could try to get one for me. 

I justify briefly my need:

A) I want to use the board as a huge RAM disk on my 13.8 MHz AT-clone.
   I know about caches, but I prefer a RAM disk with its content 
   optimized for any given application. Batch files will setup the RAM
   disk for me.

B) The size of the files I use daily in a rotating fashion is such
   that 2 Mb is a minimum. 4 Mb would give me plenty of breathing room.
   I guess 1 Mb chips at 80 ns are good enough for a 9.3 MHz bus speed.

C) I have the usual 640/384 Kb split. I would rather avoid wasting that
   384 Kb of extended memory I already have. It is also on the main board
   and theoretically accessed faster. Good if the RAM disk directory is
   kept there. However, I was disappointed when a RAM tester reported 
   several wait states on that extended memory. Especially since the
   standard 640 Kb RAM has 1 wait state write, 0 wait state read. Any info
   on this would be interesting.

D) I do not care about EMS and all that. I have no need for multitasking
   and my applications do fine with 640 Kb and temporary files. I believe
   a board without EMS capability is advantageous as it:

     1) is simple, therefore more reliable. All you need is a bus driver
        (LS244 or LS245?), a little bit of address decoding with some TTL'S,
        and the memory sockets. If I had time, I think I could make one
        up myself by looking at the circuitry of the memory board in my
        old PC clone.

     2) is probably cheaper.

     3) is perhaps faster. I can't help suspect that all that EMS circuitry,
        even when disabled, could add wait states. Anybody knows anything
        about this?

E) The potential disadvantages are that:

     1) EMS will never be available. That's all right with me as I won't
        change my mind. I'll buy a 386 when I am satisfied with the
        PS/2 software situation.

     2) access to the extended memory is done by switching the processor
        mode which I am told, is a slow process. I have no benchmark
        results on this. A couple of magazines did mention EMS software-
        driven to be the fastest option for fast 286's. That's not reason
        enough for me to go the complex EMS way. 

     3) back-filling memory to 640 Kb is not possible. I already have 640 Kb
        and I don't care for that option. I would care about back-filling
        to 704 Kb though. That's the way I have been running my PC since 1984. 
        However, it won't recognize that memory. I wrote a device driver that
        either does nothing, or modifies the amount of memory available in the
        BIOS data area and then jumps at a specific address in the BIOS to 
        reboot the PC. Any info on this capability would be great.

I looked into magazines and found and old PC-Magazine (?) which had a
comparison of memory boards. I was surprised to see that the issues
discussed there were the ones I had been thinking about. Even the 384 Kb
jump was already an option available on some boards. 

However, I doubt these memory boards are still available now. Technology
just goes too fast for such things to remain unchanged for 3 years. 
The more recent magazines mention only fancy EMS 4.0 boards which don't
interest me. There has been some contradictory discussion lately about
the Everex RAM-3000. I was sorry to hear it is probably of the fancy breed.

In the past, the queries I submitted to the net have always been answered
satisfactorily. I remain amazed at the number of people who know exactly
what one is talking about, and the potential solutions. My recent queries
about EPIC in the TeX group were answered by the author!!! I have no doubt that
if such simple boards are still available, somebody out there reading this knows
about it. If I get no reply, I can safely just forget about the whole thing for
now.

Of course, if enough interest is expressed, I'll summarize.

Thanks in advance. Francois
                       '