Path: utzoo!attcan!uunet!seismo!sundc!newstop!sun-barr!cs.utexas.edu!mailrus!cornell!uw-beaver!ubc-cs!jalbert
From: jalbert@cs.ubc.ca (Francois Jalbert)
Newsgroups: comp.sys.ibm.pc
Subject: Extended vs Expanded
Summary: Extended would appear faster
Keywords: Everex 3000 Extended Expanded RAM
Message-ID: <6258@ubc-cs.UUCP>
Date: 13 Jan 90 11:51:54 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: 90


    Hi there. A couple of weeks ago, I asked for advice concerning the 
purchase of a memory board for my AT. I also tried to justify my desire 
to acquire a extended-capable only board by mentioning its low cost, 
speed, and simplicity. I would like to thank all who took the time to 
reply, especially Timothy (Everex RAM 3000 Deluxe owner) who answered 
additional questions. The interest seems to warrant a brief report. 

    Several brands were suggested, but the Everex RAM 3000 was the most 
recommended. It also happened to be the second least expensive I could 
find in Canada! The Canadian prices were: 

    RAM 3000         3Mb in 256Kb chips  extended only          $99
    RAM 3000 Deluxe  3Mb in 256Kb chips  extended/expanded 3.2  $118
    RAM 10000       10Mb in 1Mb chips    extended/expanded 3.2  $150?
    RAM 8000         8Mb                 extended/expanded 4.0? $$$$

          where 3.2 refers to hardware capabilities, not software...

    I decided to go for the Deluxe and to experiment to see how extended 
and expanded RAM disks compare. I bought 3Mb of memory at 100ns with 1 
wait state for my 13.8/9.3 MHz AT clone. The machine already has 384Kb 
of extended memory on the main board accessible at full speed, contrary 
to the slower bus. I was very surprised to see that four 256Kb chips are 
slightly cheaper than one 1Mb chip. The only reason to go the RAM 10000 
way would appear to be if you really need the extra room. 

    I ran two benchmarks: copy 32 times a 128Kb file from the RAM disk 
to the RAM disk, and copy 8 times a 1Mb file from the RAM disk to the 
RAM disk. All with VERIFY and BREAK on. Here are the results in seconds: 

                                              128Kb      1Mb

            384Kb extended on main board      5.82       N/A
            3072Kb extended on Everex         6.81      11.81
            3456Kb all extended combined      6.37      11.65
            3072Kb expanded on Everex         7.20      13.29

    It becomes clear that extended memory is faster than expanded (EMS 
3.2) when RAM disks are concerned. As expected, the extended memory on 
the main board is faster than the one on the Everex accessible through 
the slow bus. The combination of both types of extended memory lies in 
between, as also expected. 

    To make the expanded case even less attractive, the need to load the 
EMM.SYS driver, and then the EDISK.SYS driver for the 3072Kb expanded 
RAM disk (in addition to the standard EDISK.SYS driver for the 384Kb 
extended disk) will cost you an extra 12Kb of main memory. 

    Finally, I should point out that it took me about 3 hours to get 
that Everex board running! I was ready to set it up on fire at one 
point, or give up thinking the card was incompatible with my AT clone, 
or both. I would like to, perhaps, save somebody some frustration and 
share my findings. 
    
    The problems occurred in EMS mode. First, the Everex supports 16 bit 
EMS transfers, but only if your AT is not too fast. I interpreted the 
documentation as saying the bus speed had to be 10MHz or slower. But it 
should read, a CPU speed 10MHz or slower. Indeed, a partial disassemble 
of EMM.SYS revealed some loop involving the timer chip as the culprit. 
Once I realized the problem was related to speed, I switched back to 8 
bit transfer. This allowed EMM.SYS to finally claim it had found a 
satisfactory 64Kb cache in high memory. 

    The second problem was more subtle. The EMM.SYS driver scans memory 
above 640Kb in order to set up its 64Kb cache. Don't trust its findings! 
Either the scan is not performed correctly, or some upper memory areas 
are not compatible with the 64Kb cache at hand on some AT clone. Impose 
upon the driver that it use the segment D000H for its cache. Once I did 
that, the sporadic data corruptions I had experienced in the RAM disk 
disappeared. 

    Finally, note that the popular RAM tester RAMTEST that I got from 
SIMTEL does not seem compatible with EDISK.SYS, but works with DOS' 
VDISK.SYS. At least, I think at one point I had that impression. I am 
too tired to investigate further the matter. RAMTEST reported errors in 
the 3072Kb of expanded memory, and also failed to sense the 384Kb of 
extended memory. It is perhaps sensitive to the presence of two copies 
of EDISK.SYS in memory. 
    
    Overall, I must recommend the Everex RAM 3000 Deluxe. It seems well 
built, has decent documentation, and has a very nice setup program. But 
if all you need is a RAM disk, get the simpler, faster, and cheaper 
Everex RAM 3000 extended-capable only memory board. It's $99 Canadian, 
so it should be real cheap in the states. Be careful, I found that many
dealers know only of the Deluxe version EMS 3.2 capable. There is a
simpler version extended-only available.

    Cheers. Francois
                '