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XT Turbo board problem

O

Overdrive

New Member
Joined
May 24, 2008
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5
Location
Plovdiv, Bulgaria
This is my first post here, so hello everyone and sorry for the bad English :)

I have an old XT turbo board "pim-tb10" with amd 8088-1 which runs by default at 4,77MHz and 10MHz in turbo mode by switching to 30Mhz quartz (or at least the manual says this)

The problem is that when switched to "turbo" mode the computer sometimes doesn't want to boot, the bios displays only 256k ram (i have 640k installed!!) and if I switch to turbo mode after dos is loaded it often crashes :(

Is the turbo mode overclocking the cpu or everything - isa bus, memory and etc??
The 8088-1 is rated at 10MHz, so i don't believe that its the problem.
 
What kind of ISA cards do you have installed? They might not be able to handle the faster bus speed. 10 MHz is actually over-spec for ISA; during the 286 era, 8 MHz became the standard speed for the ISA bus.

p.s. Most "10 MHz" turbo XTs actually ran at 9.54 MHz (4.77 x 2), but if yours has a 30 MHz crystal, then it might be one of the few which actually runs at 10.00 MHz in turbo mode.
 
Sounds like at least one of the memory chips can't keep up with those lightning speeds; are they in sockets and if so, in what arrangement (i.e. what kind/how many?)

But yes, always a good idea as a first step to remove any cards etc. that you don't need to boot.

m
 
I have installed the following cards:
"lcs-6210d" mfm controller with ST-225,
US Robotics modem,
SMC Lan,
the CGA Video, FDD Controller (with two 360k floppies) and Parallel/COM port card are from computer, that maybe you've never heard about - Pravetz - it's a Bulgarian made, similar to IBM 5160
http://www.old-computers.com/museum/computer.asp?st=1&c=615
but the motherboard is dead, so i changed it with this turbo board :cool:

if I use separate clocks for cpu and the other stuff will it work? I have some knowledge on electronics, so it's not a problem :mrgreen:
or they must run syncronious with one clock?
 
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That's a lot of cards. Try taking them all out except for the video card to see if the motherboard then can count the full RAM size in turbo mode, then put the other cards back in one at a time to see if any of them are causing the instability.
 
What kind of ISA cards do you have installed? They might not be able to handle the faster bus speed. 10 MHz is actually over-spec for ISA; during the 286 era, 8 MHz became the standard speed for the ISA bus.
Click to expand...
For readers of this thread, note that even 8 MHz is too fast for some AT cards. See http://textfiles.fisher.hu/computers/ASTRESEARCH/0191.tb for an example.
And there are PC/XT cards that don't run reliably over 4.77 MHz.
 
modem7 said:
And there are PC/XT cards that don't run reliably over 4.77 MHz.
Click to expand...
Reportedly the original IBM CGA board doesn't handle anything faster than that. I know it gave me constant lockups on a 386SX-33 (8 MHz ISA).

Tip: Put the most timing-critical cards in the slots nearest to the CPU, where the bus signals are the strongest and the timing delays are the shortest. (The only exception is on the original IBM XT motherboard, where the slot immediately next to the CPU is wired differently and will only work with some cards, such as the IBM RS-232 serial port card.)
 
Removed the LPT/COM card and wow - runs with no problems at 10MHz
now i can play prince of persia normally and who needs serial port when there is prince of persia :D

I'm thinking about changing the turbo quartz to 40 or 45MHz because the cpu isn't overclocked at 10MHz - it's just running at its normal speed, but I'm afraid it'll be dangerous for the hard drive
 
Wow, I really didn't know there were 16-bit ISA cards that couldn't work at 8MHz. That's pretty craptacular. I have a couple of those Rampage 286 cards. I should really check the version numbers.
 
I'm thinking about changing the turbo quartz to 40 or 45MHz because the cpu isn't overclocked at 10MHz - it's just running at its normal speed, but I'm afraid it'll be dangerous for the hard drive
Click to expand...
Your hard drive will be fine (no physical damage), but certain chips on the motherboard may be a problem. Just be prepared for the motherboard to fail.

And, will the presently fitted expansion cards handle the faster bus speed?

"Note No. 2" on page 12 of the manual is interesting. Is that the motherboard maker indicating that the motherboard tolerates overclocking to 16 MHz (340% of 4.77 MHz) if the 150 nS memory is replaced by certain 100 nS memory? That seems unlikely given that in the worst case, the motherboard may be fitted with an 8 MHz CPU that's been tested at 10 MHz (refer page 12 of manual). Maybe a CPU replacement is inferred, with the motherboard maker predicting that 8088's rated faster than 10 MHz might be released.
 
modem7 said:
"Note No. 2" on page 12 of the manual is interesting. Is that the motherboard maker indicating that the motherboard tolerates overclocking to 16 MHz (340% of 4.77 MHz) if the 150 nS memory is replaced by certain 100 nS memory? That seems unlikely given that in the worst case, the motherboard may be fitted with an 8 MHz CPU that's been tested at 10 MHz (refer page 12 of manual). Maybe a CPU replacement is inferred, with the motherboard maker predicting that 8088's rated faster than 10 MHz might be released.
Click to expand...

I think you're misinterpreting that. 16MHz would be the new core clock speed. PC and XT had a core clock of 14.31818Mhz, which was divided by 3 to get 4.77MHz for the CPU clock. I think the manual is stating you can run that particular motherboard at a core clock of 16MHz which could then be divided by two so you could run an 8MHz CPU clock.

And yes, you'd need the faster memory most likely.
 
I think that the manual says that using NEC 70108-10 (which is a 10MHz V20) gives you 340% better performance than normal XT (with 8088 ), first because speed is 10MHz and second - the V20 at the same speed is faster than 8088.

Nowhere is said that cpu will run at 16MHz, it just says "340% faster than XT"
and the clock speed is 30MHz, which means 10MHz CPU, the only way to raise the CPU speed is changing the quartz and I'll try it tomorrow :mrgreen:

at 10Mhz it runs with similar speed to an ancient 286-12 a friend of mine has - its at least 2 times faster than normal XT
 
Overdrive said:
Nowhere is said that cpu will run at 16MHz, it just says "340% faster than XT"
and the clock speed is 30MHz, which means 10MHz CPU, the only way to raise the CPU speed is changing the quartz and I'll try it tomorrow :mrgreen:
Click to expand...
Using SysChk 2.46 I get these CPU speed benchmarks with my CompuAdd 810 (NEC V20):

CPU clock speed: SysChk benchmark speed
9.54 MHz: 5.42
7.16 MHz: 4.02
4.77 MHz: 2.67

Somewhere I also have Norton SI and PC Tools SI, which also provide CPU benchmark testing, but I haven't gotten around to trying them yet.
 
I don't know. I think a 286 at 12MHz should still be over twice the speed of even the fastest 8088. Don't underestimate the power of the 286. It's a pretty quick chip. There was another guy in the forums a few weeks ago with a plan very similar in yours. I will repeat my response to him for you.

-V20/V30 chips in most real world situations are 10% faster than 8088/6s, but you can sometimes run faster if the code is heavily optimised for V series (which is pretty rare I guess). 340% speed increase is just a bogus claim, it's not possible even with V chips.

-Unless your motherboard has some special provisions built in, running over 10MHz isn't going to work. If you want to run at 15/16MHz you'll need a board designed for it. They're rare, but they do exist. My 15MHz board runs the ISA at half the CPU clock and uses 60ns DRAM and support chips that work reliably at that speed. This board performs like an 8MHz AT.
 
Overdrive said:
the computer is crashing when I start SysChk :(
is the version of dos old - I'm using 3.3??
Click to expand...
On an XT-class machine, there is a noticeable delay when starting SysChk where you might think the program has "locked up". Just sit and wait and eventually it'll come up. It's probably examining your computer (CPU, BIOS, interrupts, serial/parallel ports, etc.) during that delay.
 
OK, I fired up my trusty CompuAdd 810 and did some benchmark testing. My first try with PC Tools Pro 9.0 SI and Norton Utilities 8.0 SysInfo was a dud -- both require at least a 286. But I scrounged through my disks and found the respective programs from PC Tools 7.1 and Norton Utilities 6.01, and both work fine on an XT-class machine.

With the 810's NEC V20 CPU, the results were as follows (including the predefined comparisons each program includes):

PC Tools 7.1 SI
IBM PC-XT (4.77 MHz 8088): 1.0
CompuAdd 810 (4.77 MHz V20): 1.1
CompuAdd 810 (7.16 MHz V20): 1.6
CompuAdd 810 (9.54 MHz V20): 2.2
IBM PC-AT (6 MHz 286): 2.7
IBM PS/2 Model 60 (10 MHz 286): 4.6

Norton Utilities 6.01 SysInfo
IBM PC-XT (4.77 MHz 8088): 1.0
CompuAdd 810 (4.77 MHz V20): 1.0
CompuAdd 810 (7.16 MHz V20): 1.6
CompuAdd 810 (9.54 MHz V20): 2.1
IBM PC-AT (8 MHz 286): 4.4
Compaq (33 MHz 386): 34.7

Of course these just test raw CPU speed. When you factor in bus speed, an XT running the ISA bus at 9.54 or 10 MHz should be able to trounce an AT running the ISA bus at 6 MHz, assuming 8-bit data transfers for both. Indeed, PC Tools SI shows the MiniScribe RLL hard drive in my 810 as having better overall performance than a stock PC-AT, even though its controller is only 8-bit (a Seagate ST-11R card), versus the AT's 16-bit hardware.
 
The Norton and PC Tools SI results usually produce somewhat similar results, though I tend to lean towards PCTools. I have a hard time believing a 6MHz AT scores a 2.7 in PCTools while an 8MHz AT scores a 4.4 in Norton. I believe in PC Tools the 8MHz AT will score 3.6 which makes more sense if you do some basic math. Older versions of Norton SI had some serious issues accurately reporting the speed of V20/V30 chips. If you use version 4.x you will find the results are much higher. I still find the results of later versions of norton to be a little goofy sometimes.

I would tend to think that when it comes to playing DOS games CPU and memory transfer rates would be more critical than HDD transfer rates.

Additionally, it's a little unfair to be comparing the disk system of a late model turbo XT to the first AT 286 ever made. Put a decent 16-bit IDE or SCSI system into the AT and it will beat the pants off any XT in disk intensive activities. What does a 10MHz XT bus peak at? ~700kb/sec? The 6MHz AT bus should be capable of around 3-4mb/sec.

I agree for the most part a 10MHz V20 system puts up a good fight against a 6MHz AT, but it barely competes at the 286 level...much less a 12MHz 286. I still use my XT and AT systems on a fairly regular basis, and in this case the benchmarks don't lie (too much).
 
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Anonymous Coward said:
Older versions of Norton SI had some serious issues accurately reporting the speed of V20/V30 chips. If you use version 4.x you will find the results are much better. I still find the results of later versions of norton to be a little goofy sometimes.
Click to expand...
Norton SI 6.01 claims my NEC V20 is "clocked at 15 MHz" when it's actually running at 9.54 MHz. And even at 4.77 MHz it claims "10 MHz".
 
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