Antiquities: the merciless upgrade of the 386th computer

Merciless and meaningless! In the process of building the 386th computer "at maximum speed" I wanted to arrange something like this, in addition to a completely logical study of any periphery. I chose between screwing water cooling with backlight and processor upgrade, although I already have the most powerful AMD processor with a frequency of 40 megahertz. But there was a way to make the “almost 486th” computer out of the 386th computer, and that was interesting.

Kits for a budget system upgrade using next-generation processors have existed since the beginning of the era of IBM PC-compatible computers. Iron in those days was easier, and to adapt, for example, the 386th processor for the 286th motherboard was not difficult. The competition in the integrated circuit market was higher: in addition to the current Intel and AMD, Cyrix, Texas Instruments and IBM were present in the processor market. The industry has not yet completely got rid of the legacy of the early days, when the release of processors by different companies according to general specifications was commonplace. But nobody canceled reverse engineering either, because of which sometimes very interesting specimens were obtained, seemingly compatible with the “originals”, but having a lot of their own features.

In 2020, upgrading the old system probably does not make sense at all, only if out of curiosity. It’s easier to build a real 486th computer if you really want to. But in the end, I repeated the path of the owner of the 386th computer, which wants to save money, increasing productivity with little effort. So, imagine yourself in the place of a wealthy computer fan year that way in 1994. You have just completed a successful transaction by exchanging a grain car for a garage in the suburbs, and it for two used Zaporozhets. Selling them in the car market, you get a small amount in cash, too little for a new PC based on 80486 or even on the Pentium. And I want to finally play normally in Doom. What to do? I'll tell you now.

All articles on the topic:

0. 1992 in the computer press
1. Consider the motherboard of the 386th computer
2. The benchmark of the 386th processor and the dashing nineties
3. Difficult choice of sound card for DOS games
4. Features of Sound Blaster Pro 2
5. Roland MT-32, an alternative sound for DOS games
6. Ruthless upgrade of the 386th PC - <- you are here The

diary of a collector of old pieces of iron I keep in Telegram .

Merciless motherboard upgrade
Fortunately, I didn’t have to trade “Zaporozhtsy” on the market, and I started the computer upgrade by replacing the motherboard. Let me remind you that initially I had this motherboard for the 386th processor:

Last year, in the process of purchasing components, I purchased another motherboard “without a guarantee of operability”, with a traditionally leaking battery, but with 256 kilobytes of cache memory. The board turned out to be quite operational, and the damage from the electrolyte was minimal. The photo already has a new battery installed:

The motherboard model is ISA-386SIQ. There are specifications on stason.org that says the board manufacturer is Asus. This is not indicated anywhere on the board itself. The BIOS of this model is a bit more modern: there is a utility for working with a hard disk for low-level formatting, but there is still no automatic detection of parameters. You can skip the RAM test above 1 megabyte, thus speeding up the download and turn off the cache. But the most important thing: on this board there are two additional eight-bit expansion slots, and in total you can install eight boards on it instead of six. HardMPU MIDI interface for the Roland MT-32 synthesizer will be installed in one of the eight-bit ports . Over time, I expect a shortage of slots, so such an expansion is very useful.

When replacing the board, it was necessary to make sure that the initial set of AMD Am386DX-40 processor and coprocessor works with the same performance. For this, I used the benchmark System Speed ​​Test or SpeedSys:

Compared to previous measurements, the difference is small: the number of points in the processor test decreased slightly (6.85 instead of 7.07), but the speed of working with memory increased noticeably from 27 to 31 megabytes per second when working with cache memory and from 12 to 17 MB / s for ordinary memory. Most likely this is due to the only downgrade in the new configuration: I reduced the amount of RAM from 32 to 16 megabytes. Even 16 megabytes for such a system is a lot, and 32 brought a lot of inconvenience (long testing at boot time, errors in some old programs and games). The expected performance increase in Windows 95 did not happen: on the 386th platform, this OS seems to be limited by the processor's capabilities, and not by the amount of memory.

Add one more benchmark: classic CheckIt, a multifunctional utility for evaluating system operation parameters. It returns two digits: performance for integer operations and for floating point calculations. In other words, the capabilities of the central processor and the coprocessor 80387 are tested, which will come in handy during the next upgrade. At the same time, CheckIt compares the power of your system with the IBM PC XT computer (1983, Intel 8088 processor at 4.77 megahertz). While it turns out 34 times faster, but this is only the beginning.

Merciless coprocessor upgrade
Not a mandatory upgrade (there are no obligatory upgrades in this article), but after I started collecting pieces of silicon with gold-plated legs, it was hard to stop.

Cyrix FasMath is considered one of the fastest coprocessors for 386 systems. This in itself is beneficial only in a small number of specialized programs, but during the upgrade it turned out that the original IIT chip was not "friendly" with the new processors - the computer simply did not boot. Everything worked fine with FasMath, and if so, let's see what this gives us.

Not much 3% FPU performance gain. The benefit of Cyrix FasMath is that it works stably with faster processors.

I wanted to add some real program to the two synthetic benchmarks. Doom is ideally suited here: the game really works well on 486 systems, on 386 it slows down, and it would be logical for the owners of such "outdated" computers to upgrade to "Doom" to work. I tested Doom on the "maximum" graphics settings (in fact, with a full-screen image, even without a menu bar). The starting result for 386DX-40 is 6.61fps .

Half measures. Cyrix Cx486DLC-40 or TI TX486DLC-40

What are the differences between 80486 and 80386 processors? The 486th processors have on-board cache (8 kilobytes at first, 16 later), the floating-point unit is built-in (there is no need for an external coprocessor, although 486SX models without FPUs were released), an optimized computing pipeline that executes some operations for fewer measures, new instructions. The first processors of 1989 had a frequency of 20 megahertz, in 1991 a processor with a frequency of 50 megahertz was released, after which the practice of doubling, tripling, and even quadrupling the frequency was introduced. This was necessary, since it is impossible to infinitely increase the frequency of the system bus - already at 50 MHz there were problems with peripherals on the VLB bus. The first 80486DX2 processors had a frequency of 40 to 66 megahertz, with a system bus frequency of 20-33 megahertz.The socket has also changed - the 386th processors have 132 legs, 486 have 168 legs (later 169, 237 and 238, depending on the model).

But these are the real 486s. Released in 1992, the Cyrix Cx486DLC processors were, firstly, the result of “clean room” reverse engineering, and secondly, they did not have all the capabilities of full-fledged 486 processors. There was a cache on the chip, but of a smaller volume, only 1 kB. There was no FPU - these processors require an external coprocessor. Wikipedia describes these chips as “a core from 386 with cache memory and support for instructions from 486”. In other words, you should not expect from Cx486DLC or TI 486DLC (these are essentially the same processors with different labels) with a frequency of 40 megahertz the same performance as a full 80486 with the same frequency.

But for the 386th computer, this is the simplest and most easily obtained upgrade: take out Am386, insert Cyrix and everything works. Problems can arise only with the cache memory: for some systems, it must be forcibly “turned on” by a special utility:

In my case, even a utility is not required: cache is enabled by default. But here it becomes clear that we are starting to use not the most standard solutions. The BIOS tells us that some “80486” is installed on the motherboard, even without indicating the frequency. Speedsys, which is able to determine the first level cache in the processor, does not see it in Cyrix / TI, but it does not correctly determine the frequency. The specialized utility CacheCHK does not see the cache, and it is only possible to verify operability by means of forced shutdown and comparison. So, the results for 486DLC-40 without cache:

21% increase in productivity in CheckIt and 31% in SpeedSys. Doom got 7.45fps, + 12%. Turn the kilobyte of cache back and see if there is a difference:

Just as it is! In comparison with the basic configuration, the increase is 33%, in SpeedSys - 42%. In Doom - 9.64fps, + 45%. Even FPU performance according to CheckIt has grown by 43%. I would stop and calm down on this, but I would like even a little more power. "Upgrades" 386-486 were released by many companies, but the problem is that these processors are not so easy to find now. I suspect that the upgrade of 386 systems quickly ceased to be relevant, and more powerful solutions, although they were available, were already sold in very small quantities.

Full measures. TI 486 SXL2-50
I was lucky, I bought a new boxed kit to upgrade the 386th computer. It was not cheap and, as I have said more than once, it is quite pointless. But buying something very ancient in a state “like in a store then” is a special joy for any collector of old trash.

Inside are installation instructions (with an error in the most important place - where it is indicated how to orient the processor relative to the motherboard!), The TI 486 SXL2-50 processor in the PGA168 version, the PGA168-PGA132 adapter, a small heat sink on a thermal tape, a diskette with a driver and an extremely useful tool for carefully removing processors from the socket.

The adapter turned out to be a bit more complicated than just connecting one leg to another.

SXL2-50 processors were also available in a version that plugs directly into the 386th socket, without adapters, but even more interesting. This upgrade brought with it a new set of problems. The TI processor uses frequency doubling - with regular 25 megahertz it works at fifty. The frequency of the system bus on my motherboard is 40 megahertz, and it’s clear that this processor will not work at 80 MHz with doubling. How to change the frequency on the motherboard? Now it can be done right in the BIOS, on real 486s - jumpers, but on the 386th there is only one way: to replace the frequency generator.

While I ordered and waited for the delivery of suitable crystal oscillators, nothing prevented me from trying to run this processor at a frequency of 40 megahertz without doubling. 486 SXL2 is equipped with a cache of 8 kilobytes, as in “adults” 80486, which in itself should provide a performance boost.

Unlike the DLC40 with a kilobyte cache, Speedsys recognizes 8 kilobytes of SXL2 cache. The speed of data exchange, however, is only slightly faster than the speed of working with the cache on the motherboard: 35 megabytes per second versus 31. In Pentium III, the built-in first-level cache is one and a half times faster. Nevertheless, we have an increase (compared to the base 386DX-40) by 42% according to Speedsys.

So the adapter and the processor itself look on the motherboard. Long expansion cards in this design can abut the heatsink:

+ 51% in CheckIt. Performance in Doom rose to 10.37fps, + 56%. I overclocked my 386th PC one and a half times! Let's go back to the system bus frequency. For a 40 megahertz processor to work, a 80 MHz crystal oscillator is required, respectively, to get 25 MHz I ordered a new 50 MHz oscillator. Decreasing the system bus frequency is a controversial solution, it brings a drop in the speed of working with RAM and cache. Will doubling the processor frequency compensate for this? Test results at an honest 25 megahertz returned the system performance to the level of the original 386DX-40. Turn on doubling: this is done using the console utility, the launch of which will have to be written in autoexec.bat. So, the final results:

20904 points in CheckIt, an increase of 76%, 60 times faster than IBM PC XT! But the speed of floating-point calculations has fallen - due to the lower frequency of the system bus.

But the result in Speedsys was less than in 40 MHz without doubling. The speed of the cache on the chip has increased, the speed of the cache on the motherboard and regular RAM has fallen. The results of measuring the throughput of the video card and hard drive decreased. Most importantly, the result in Doom, as in a real application, remained the same as in the “40 MHz without doubling” mode - 10.39 fps versus 10.37.

I will finish this quest for now, although there are ways to increase productivity even more. Can I overclock this processor? An attempt to start it with a frequency of 33 MHz and a doubling of the processor frequency to 66 MHz failed - it does not start. Judging by the reviews on the Vogons forum, the maximum possible here is 55 megahertz on the processor and 27.5 on the bus. You can try changing the settings of the processor itself - there are quite a lot of them, and not all optimizations are enabled by default.

Finally, you can try to get either an even more powerful “upgrade” or a full-fledged active adapter that allows you to install the “real” 486th. But wait, because my adapter allows me to install the 486th processor. The main thing is to comply with the power requirements - the model must be with an operating voltage of 5 volts. And of course I tried, and of course it didn’t work out for me - the IBM DX2-66 processor from the picture above, tested on a normal 486th motherboard, didn’t work on 386. Ideally, you should look for IBM processors in the Blue Lightning series, designed to work on 386 systems. Such were produced with frequencies up to 100 megahertz, but are now a collector's rarity. Finally, in this threadon the Vogons forum you can see the benchmarks of the 386th PC with a 160 MHz AMD Am5x86 processor installed through a more complex (than mine) 486HPi adapter. This is a very fast 386th, but the same processor at the same frequency, installed in the normal 486th motherboard, works on average one and a half to two times faster.

By the way, how is my franken386 compared to the real system on the 486th processor? A little later I will find out in practice, but for now, you can look into this large collective testing of 80486 on the Vogons forum. In the Speedsys test, a cheap 486SX with a frequency of 25 megahertz scored a comparable 9.1 points. The result of 486DX-33 is 12.5 points.

Prices
How much did such an upgrade cost? In June 1994, PC Magazine lists the following prices:

145 dollars ($ 250 including inflation) for Cyrix or TI 486DLS-40 is probably the best purchase, 33-50% performance gain after the simplest upgrade. The TI SXL2-50 costs $ 299 ($ ​​515), and this is a dubious purchase: the two 486DLC prices give only 30% of the performance gain in the best case scenario, and 7% in Doom. But pay attention to the widest range: upgrade to the “type 486” was possible even on 16-bit systems with 80286 or 386SX processors. There is even an IBM BL3 with a triple frequency of 100 megahertz and a cost of $ 749 ($ 1292).

How justified was it? A new computer based on an 80486 processor with a frequency of 66 megahertz (25 points in Speedsys, three times faster than my computer after the upgrade) cost $ 1,300-1600 ($ 2250-2700), but it is a system with a case, a keyboard and a monitor. Independent upgrade was less common then, but the advertisement above gives an approximate idea of ​​this option. A motherboard with the same DX2-66 costs $ 430 ($ 740). Most likely you will have to buy both memory and a VLB standard video card - the same Doom at some point rests on the performance of 16-bit video, and not on the processor. The conclusion is this: if you upgraded yourself in 1994, then it was quite justified, but you should not have expected performance equal to the “real” 80486. It is much worse if you sold such a DLC under the guise of (and at a price) of the real 486th .In about this scenario, I was sold Celeron in 2001 under the guise of a real Pentium III. But this is a completely different story.

The final table with the results. Available on Google Docs here .

findings
In this ambiguous (and expensive, considering the cost of a sealed box with TI SXL2) method, I got the opportunity to play on the 386th computer in Doom, not only at the minimum. The “full screen” indicators are still far from ideal, but if you slightly reduce the size of the window, then everything works fine. Of course, I asked myself such a typical collector’s question: I just had the authentic 386th, and now it’s not clear what, some 486 is at the minimum, and why is this all? Probably it was important for me to repeat the experience of the owner of such a system in the early nineties. I got a very non-standard system, which is still compatible with old hardware and software. If desired, I can "slow it down" to the level of 386 or even the 286th PC: disable frequency doubling, cache on the processor and motherboard. The pleasure of spinning old glands that,besides, they work and are not even buggy - it is worth the cost.

Thus, I finalized the basic configuration of my 386th computer. It turned out this:

• TI SXL2-50 processor with 8kB cache
• Motherboard with 256KB cache (20ns) and 8 ISA expansion slots
• 16 megabytes of RAM with parity (4 modules 4MB 60ns)
• Diamond SpeedStar Pro graphics card with Cirrus Logic GD5426 chipset and 1 megabyte of memory
• WinBond multicard with IDE, FDD controllers, two serial and parallel ports
• Hard disk USB flash drive 256 MB per IDE-CF adapter
• Sound Card Creative Sound Blaster Pro 2
• HardMPU MIDI controller and Roland MT32 external synthesizer

Construction continues!

Source: https://habr.com/ru/post/undefined/