XT Turbo board problem

[Overdrive]

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.

[vwestlife]

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.

[MikeS]

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

[Overdrive]

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?

[vwestlife]

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.

[modem7]

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.
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.

[vwestlife]

And there are PC/XT cards that don't run reliably over 4.77 MHz.
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.)

[modem7]

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?)
Manual available at http://members.dodo.com.au/~slappanel555/manuals/10%20Mhz%20PIM-TB10%20Turbo%20Mainboard.pdf

[Overdrive]

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

[Anonymous Coward]

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.

[modem7]

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
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.

[Trixter]

"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.

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.

[Overdrive]

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

[vwestlife]

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:
Using SysChk 2.46 (http://www.syschk.com/) 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.

[Anonymous Coward]

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]

Using SysChk 2.46 (http://www.syschk.com/) 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


the computer is crashing when I start SysChk :(
is the version of dos old - I'm using 3.3??

[vwestlife]

the computer is crashing when I start SysChk :(
is the version of dos old - I'm using 3.3??
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.

[vwestlife]

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.

[Anonymous Coward]

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).

[vwestlife]

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.
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".

[Anonymous Coward]

That's interesting. I always found it odd that Norton was the ONLY program that could properly identify my 15MHz V30 as a 15MHz V30. Well, now I know the real reason: pure coincidence!

[vwestlife]

I pulled out some old JDR Microdevices catalogs, and here are the Norton SI 5.0 benchmarks they have listed for the various motherboards they offered ( * indicates the presence of onboard L2 cache):

8088-10: 2.1
286-12: 9.2
386SX-20: 10.0 (?)
386SX-16: 11.1
286-16: 11.8
386SX-33: 15.3
386DX-25: 15.6
386DX-33*: 35.7
386DX-40*: 43.1
486SX-20*: 54.0 (386/486 combo board)
486DX-33*: 71.3 (ISA)
486DX-33*: 72 (VLB)
486DX/2-66*: 92 (ISA)
486DX/2-66*: 99 (VLB)
486DX-50*: 108 (EISA)

They also gave Landmark 2.0 benchmark results, but Landmark appears to be a more simplistic clock speed test because it shows a 486DX/2-66 being drastically faster than a 486DX-50, while Norton SI actually shows the DX-50 being faster than the DX/2-66 due to its higher bus speed.

Also interesting is how easily a fast 286 can match or even beat a low-end 386. It makes sense, because when running real-mode code without any 386-specific optimizations (and without an L2 cache), the 386 is essentially equivalent to a 286 running at the same clock speed.

[Trixter]

They also gave Landmark 2.0 benchmark results, but Landmark appears to be a more simplistic clock speed test because it shows a 486DX/2-66 being drastically faster than a 486DX-50, while Norton SI actually shows the DX-50 being faster than the DX/2-66 due to its higher bus speed.


But a DX-50 has a bus speed of 25MHz, not 33... Just like the DX4-100's are so named because they have, again, a 25MHz bus. Confused.


Also interesting is how easily a fast 286 can match or even beat a low-end 386. It makes sense, because when running real-mode code without any 386-specific optimizations (and without an L2 cache), the 386 is essentially equivalent to a 286 running at the same clock speed.

Clock for clock, a 386 is still faster. Nearly every opcode runs in less cycles, plus a DX has a 32-bit bus. But I have seen a 286-20 beat a 386-16sx, because both were on equal footing (386sx uses 16-bit bus just like 286).

I am beginning to think that there is slowly increasing demand for vintage PC benchmarking software that doesn't utterly suck. Landmark, Norton, are all quite terrible because they tried to apply a single metric to unknown/future hardware. Today, we have the benefit of how history played out, so a better benchmark tool could be written. I'll think about it in bed tonight and try to work out some more details.

[vwestlife]

But a DX-50 has a bus speed of 25MHz, not 33... Just like the DX4-100's are so named because they have, again, a 25MHz bus. Confused.
No! This is a real 486DX-50 we're talking about. Full 50 MHz bus speed, no clock multiplier! 8)

http://www.chipdb.org/data/thumbnails/320/80486dx-50_sx546_cpuswe.jpg

The DX-50 was well known to each DX/2-66's for lunch in real-world use, but it fell out of favor because it was so difficult to get VESA Local Bus and PCI cards to work at 50 MHz, or even 40 MHz (33 MHz was the design spec speed).

[Anonymous Coward]

It still seems there is confusion out there about the 486DX-50 and the DX/4-100.

There are two different 50Mhz 486 chips. The 486DX-50 uses a 50MHz FSB. There is also the more common 486DX/2-50, which uses a 25MHz bus as you mentioned. However, the benchmark label and score provided seem to indicate a 486DX-50 was used.

DX/4 is a clock tripled, not clock quadrupled as the name implies. Therefore a 100MHz DX/4 has a 33MHz bus. There is also a 75MHz version that uses the 25MHz bus.

[vwestlife]

DX/4 is a clock tripled, not clock quadrupled as the name implies. Therefore a 100MHz DX/4 has a 33MHz bus. There is also a 75MHz version that uses the 25MHz bus.
Yes, the "DX/4" should really be a "DX/3". BUT!!! You can also run a DX/4-100 in clock-doubled mode: 2 x 50 MHz instead of 3 x 33 MHz! Intel never really promoted that mode because it'll cause many VLB and PCI cards to crap out, just like the DX-50, but it does work and is not "overclocking" -- 2x50 was part of the design spec.

The AMD 5x86 also supports 3 x 50 MHz mode. They released a very small number of true 150 MHz 5x86s, but you can do it just fine on a "133 MHz" 5x86 (as well as 40 x 4 = 160 MHz).

http://www.chipdb.org/data/thumbnails/23/Am5x86-P75+_150ADW.jpg

[Vlad]

Actually there was a DX/3, it was just never released.

[Anonymous Coward]

About intel's policy on 50MHz bus on their DX/4 chips....

actually not all of their DX/4s were rated to work on the 50MHz bus. They used to have this up on their website, but actually only a certain stepping officially supports 2x50MHz mode. I believe that model was of the write-thru variety. Though, all of their chips seem to work with the 2x multiplier. In the official documentation for the chip there was also mention of a 2.5X setting, but it doesn't work. Rumour has it the 2.5X multiplier probably would have been used on said DX/3.

50MHz bus generally isn't worth it on 486 boards because of all the extra wait states that need to be added for the cache and main memory.

[Vlad]

The 2.5x multiplier was the failed DX/3. I dunno why it didn't make it, but the DX/4 was released in its place.

[Anonymous Coward]

It made sense not to release a chip in between the DX/2 and the DX/4. The difference in performance would have been almost undetectable. The bigger mystery is why they kept the name DX/4 and didn't rename it DX/3 instead after the real DX/3 was canned. I've heard people say that "DX/4" gives the impression of being twice as fast as a DX/2.

[vwestlife]

It made sense not to release a chip in between the DX/2 and the DX/4. The difference in performance would have been almost undetectable. The bigger mystery is why they kept the name DX/4 and didn't rename it DX/3 instead after the real DX/3 was canned. I've heard people say that "DX/4" gives the impression of being twice as fast as a DX/2.
Perhaps it was because IBM beat them to the punch by releasing the first clock-tripled, 100 MHz x86 chip: the "Blue Lightning" 486BLX3-100.

Number-jumping was also in vogue back then: witness Microsoft's MS-DOS 6.0 and 6.2, versus IBM's PC DOS 6.1 and 6.3.

[Vlad]

Intel has always been kinda cryptic and strange when it comes to code names and version numbers. Who knows why they went ahead and released it as the DX/4. Probably just wanted to stick to the version line. Version 3 didn't work so release the improved (?) Version 4. *shrugs*

[Anonymous Coward]

I'm still bitter about the lame "667MHz" Pentium III. I would have much rather had a 666MHz Hexium II.

[vwestlife]

BTW, I just got a Tandy 1000RL, and for an XT-class machine, this thing is QUICK. Its 9.54 MHz 8086 handily beats my CompuAdd's 9.54 MHz V20 in benchmarks (2.6 vs. 2.1 in Norton SI; 2.8 vs. 2.2 in PC Tools SI). The only downer is that it is soldered in place and can't be easily upgraded to a V30. The speed of its 20 MB Seagate IDE-XT hard drive is also well above average for an XT -- and of course, booting up DOS and DeskMate from ROM is even faster. :D

DeskMate even includes a crude form of MOD-like music tracker: you can compose and play multi-voice music, and instead of synthesizing the tones, it uses digitized samples of real instruments, like piano, cello, clarinet, etc. You can even record and edit your own audio samples using its microphone/line input. Neat stuff! :)

[Trixter]

Great find! The TL and RL series were always my favorites with the better graphics, better audio, and DOS in ROM. They're great for writing hairy assembler programs -- when you lock up the machine, just hit reset and you're back at the DOS prompt in 2 seconds.

[vwestlife]

Great find! The TL and RL series were always my favorites with the better graphics, better audio, and DOS in ROM. They're great for writing hairy assembler programs -- when you lock up the machine, just hit reset and you're back at the DOS prompt in 2 seconds.
Try SETUPRL /A ... which lets you adjust all the nitty-gritty details of the machine, just like advanced CMOS setup on a 386. It even lets you switch the built-in IDE-XT controller between PIO and DMA modes... that's the first time I've seen that on anything less than a 486! :eek: (PC-Check claims the stock 20 MB IDE-XT hard drive is running at 1:1 interleave, which is amazing for an XT-class machine!)

[IBMMuseum]

Perhaps it was because IBM beat [Intel] to the punch by releasing the first clock-tripled, 100 MHz x86 chip: the "Blue Lightning" 486BLX3-100...

More commonly known as the 486DLC3-100. It's close to the PQFP 386DX (AMD used this packaging for their last 386DXs) pinouts, and designed to more easily implemented into that class of motherboard (or "planar", as IBM did have unpopulated solderpads that were for this CPU on a few of their late-model PS/2s). In fact the "D" in "DLC" denoted that it was intended as an upgrade for the 386DX, just as IBM's 386SLC, 486SLC2 (clock doubled, most common as 50MHz than 66MHz), and 486SLC3 (clock tripled, but more common as 75MHz than 100MHz) were upgrade CPUs for 386SX-class systems (more correctly stated as 16-bit data bus, 24-bit address bus systems).

The wild thing is that the same package can be configured in it's hardware implementation as a 486DLC3 or 486SLC3! IBM increased the L1 cache size on their CPUs for better performance (the 386SLC had 8Kb, the 486SLC2, 486SLC3, 486DLC2, and 486DLC3 had 16Kb). Despite the name, the 386SLC is able to run all Intel 486SX instructions too.

And to be fair, "IBM beat them to the punch" by being licensed to modify the original Intel 386SX/386DX codemasks. All of the CPUs I've mentioned here have a dual copyright printed on top: "1985 Intel, 1992 IBM". Yes, IBM did vastly improve the performance, but it is derivative from an originally Intel work.

[Mike Chambers]

not sure if somebody else already said this on these 4 pages, so if this is a repeat sorry. does your board have a jumper that lets you modify the RAM access speed? if so, play around with that and see what happens.

i have an XT turbo board made by PC's Unlimited that has a jumper that switches from 100 to 120 ns RAM speed.