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Anonymous Coward



Joined: 20 Nov 2004
Posts: 589
Location: Shandong, China

PostPosted: Wed Oct 29, 2008 5:46 am Reply with quoteBack to top

Here are a few interesting things I've found on my XT.

-12MHz XTs are definetly bad mojo. I overclocked my 10MHz XT to 10.7mhz, and even that was enough to make my EMS and VGA card angry...these are not old cards either.

-disk caching (smartdrv,pc kwik) does not help speed up access on my XT at all...infact, it is about 40% slower than without. I am wondering if perhaps my disk system is faster than EMS memory in some way. Very strange behaviour.

-model M keyboard do not work properly on my XT clone. This may to apply to other XT clones too. The model Ms supposedly auto detect between XT and AT interface, but something on m XT confuses it. I'd like to find a way to hard wire it in XT mode if possible

-EEMS cards seem to be able to do some page frame tricks that LIM 4.0 boards can't. I can get 176kb of UMB with an AST rampage versus 144kb on a RAMQuest 8/16.

-Some programs mistake my 10MHz V30 for a 15MHz chip. Perhaps they think it performs like a 15MHz V20.

-V30 chips are a *lot* faster than V20 chips. I would estimate almost 50% faster according to several benchmarks I have ran.

-The FASTV20 program is much better than I expected. It gives a speed boost at least equal to that of the V20 over an 8088. For some reason it's very difficult to find. Uncreative Labs download section is one of the few places on the internet that has this program.

-Many CPU benchmark programs give inaccurate picture of V20/V30s. A 10MHz V30 with FASTV20 and 0ws memory should score about 3.8 IBM PC/XTs. Perhaps similar to a 7MHz AT.

-DOS can be loaded in UMB on an XT if you have an EMS card, run QRAM, and DOS-UP.SYS, providing at least 619kb of free coventional memory (depends on the size of your EMS driver)
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ryan



Joined: 19 Apr 2006
Posts: 261
Location: WisConSin

PostPosted: Thu Oct 30, 2008 11:55 pm Reply with quoteBack to top

1. 12Mhz = OC'd XT bus any way you slice it

2. Given most HD's can saturate the XT bus on consequtive reads I would assume a disk cache on an XT would only be of benefit on a fast XT with a very slow HD. I also seem to remember that disk cache programs on an XT should never have more than 64kb of ram devoted to them, you should test that on your ems card. (I also seem to remember some disk cache programs made for XT's only that used 16kb ram and did indeed speed up performance, now to look for one in my archive)

3. Not all Models M's can auto sense (i have one that works and one that doesn't on an XT, they both look identical), many model M's are AT only and I do not believe there are any marking differences between an AT model M and a Hybrid, needless to say when something is made under the same model number for many years there can be many bastardizations hiding under the lable.

4. What is EEMS?

5/6/7. A V30 like the Intel 8086 is significantly faster than the V20/8088. A properly implimented 8086 is nearly the same speed as a 286 because the memory bus should be 16bit and the 8086 is a KISS processor that simply works more effectively much like the comparison between a 286 and a 386sx. The 8 bit bus really does mess up performance, sadly many early 8086 systems were setup as plain 8 bit with 8 bit memory address because the designers were lazy, the 8086 is a real 16bit chip with a 16bit bus.

8. The best way I've found of clearing up conventional memory on an XT is to just use an older version of DOS but it is amazing the potential XT's had should more software have been made for expanded memory.
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Anonymous Coward



Joined: 20 Nov 2004
Posts: 589
Location: Shandong, China

PostPosted: Fri Oct 31, 2008 4:53 am Reply with quoteBack to top

I don't know if an 8086 could ever be as fast as a 286 at the same clock speed, but it's definitely much faster than an 8088. A v30 seems to offer about 80% of the performance of the 286. I'm guessing the board I'm using is a true 16-bit one, being that it was probably one of the last XT boards ever made.

I tried your advice and setup a smaller disk cache. The results were even worse than before. Do you think having a 16kb software disk cache would be useful if the drive has its own 256kb SRAM cache? I'd still be interested in your programs if you can find them.

AST's EEMS was a competitor to the EMS 3.2 specification. EEMS was superior in pretty much every way. LIM 4.0 adopted most of the EEMS features, but I don't believe the two are 100% compatible (even with new drivers).

I used to agree that using an older version of DOS was a good way to free up conventional memory, but the QRAM UMB manager changed my mind.
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Puckdropper
Site Admin


Joined: 02 Oct 2004
Posts: 760
Location: Not in Chicago

PostPosted: Fri Oct 31, 2008 6:44 am Reply with quoteBack to top

ryan,

Is that KISS processor you refer to just a "Keep is simple, stupid" processor, or a reference to an actual architecture? A quick Google Search turns up nothing of interest, but this class of machines was in the "before the Internet" time so minor things are often forgotten.

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ryan



Joined: 19 Apr 2006
Posts: 261
Location: WisConSin

PostPosted: Tue Nov 04, 2008 12:36 am Reply with quoteBack to top

Puckdropper wrote:
ryan,

Is that KISS processor you refer to just a "Keep is simple, stupid" processor, or a reference to an actual architecture? A quick Google Search turns up nothing of interest, but this class of machines was in the "before the Internet" time so minor things are often forgotten.


The former, the 8086 did not need to double up two 8bit words into a 16bit word and could run "native" just like a 286 compared to a 386sx. As a result an 8086 on a 16bit memory bus is always at least 50% faster than an 8088 due to the improved bandwidth.
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