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Old 16th May 2020, 5:37 pm   #21
audion_1908
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Default Re: How long can a computer last?

Quote:
Originally Posted by Vintage_RC View Post
I've had failures in PCB vias with multi layer boards in PC's. All PC's internal parts are subjected to regular thermal cycles in normal use and vias which are a very small thin form of inter layer connector are particularly vulnerable to thermal stress cycles. In my experience the weak point is actually the connection between the via and an internal track. The area of the connection is extremely small. The failure mode usually starts as an intermittent fault which can often be made to come and go by flexing the PCB.
I don't see a way of fixing this without digging the PCB open and rebuilding it, no doubt making more problems, so careful handling of the board avoiding bending and shock also avoiding heat cycling would help, but that would be the invisible history of the device?

When I was in college in the early 2000s, I got a free mother board like this, it had to be pressed in just the right places to work, I glued match sticks under the mb in little stacks, it only worked overclocked from 75mhz to 90mhz otherwise the keyboard would not work? and then all the I/O died one port at a time! so I put in an ISA multi I/O card savaged from a 286, the psu was dried up and put interference on the CRT, but worked reliably for 24/7 running the text windows nt4 version of SETI@home on 32mb of ram running Windows 95, I think all the PCI bus was dead and so used only ISA cards?

I have read about how vias are made and it seems like chemistry voodoo! Is it possible the spot likely weak PCBs? One way to fix this would be like with the Amiga 500, new updated PCBs are being made and people transferring the old chips to a new motherboard! But this seems slightly extreme, but very cool.

am I wrong in thinking because the high frequencies invoved patch wires can't be used to bypass the bad vias? How hard is it to find the bad vias to bypass? Would it help to have a good board to compare?

I always thought my old Pentium 75 motherboard had cracked tracks internally I didn't suspect the vias!

Anyway I've got a little bit off track, I was talking more about preventative maintenance than repair

How did you diagnose and repair it?
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Old 16th May 2020, 5:38 pm   #22
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Default Re: How long can a computer last?

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The Voyagers are of course powered by a nuclear reactor,
Not quite (although nuclear decay goes on) a Radioisotope Themoelectric Generator https://en.wikipedia.org/wiki/Radioi...tric_generator

These are not as mass/energy efficient as a fission reactor by any means but they are everso reliable, simple and don't need a control system.

20 light hours away at 160 bits/second, that works out at 2x10^12 bits a second at one mile. And all I get is a paltry 50x10^6 bits a second. A million time worse!
 
Old 16th May 2020, 5:50 pm   #23
audion_1908
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Default Re: How long can a computer last?

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Originally Posted by SiriusHardware View Post
I didn't have time to read the document but one factor which uniquely affects computers and computer controlled devices is the longevity of the firmware code - in older devices for example the programmed firmware code may be held in EPROM where the initial programming is performed by forcing a charge (or no charge) into each memory cell.

Over time this charge gradually fades away and it is a matter of when, not if, the firmware will begin to fail as bits gradually return to their unprogrammed state. So one essential bit of maintenance which needs to be performed on equipment with firmware in EPROM is to 'refresh' the EPROM code by over-programming it every few decades. Every time you do that, you reset the 'data fade' clock back to zero. If you have equipment with EPROMs which were programmed forty or more years ago, they may be getting very close to the onset of bit-rot now. You'll put them away working, and then the next time you get them out they'll be dead or going haywire. The internet is a terrific resource here, though - wherever it is possible to read and archive firmware you will generally find that someone, somewhere, has already done it. With the rise of emulation, firmware for home computers of the 8 and 16 bit eras has been especially widely preserved.

Systems with their firmware programmed in MASK ROM or one-time programmable PROM should not be subject to these problems, although there are no doubt other interesting ways in which they can fail.

More modern computers / computer controlled devices will typically have their firmware code stored in 'flash' memory and this, too, may be subject to gradual degeneration of the firmware code over time although with flash still being a relatively recent technology, that will be for the next generation to worry about.

Whereas with discrete EPROMs it was a simple matter to read and back-up the firmware code while it was still working, most microcontrollers are designed to make their internal code difficult for third parties to read out so it would be much harder to refresh the code in those cases.
So backup all the firmware no matter how it's stored, and reflash your eeproms and eproms every 20 years and flash every 10?
Do they have a parity check or could one be added to detect the start of bit rot on boot? or is it better to add a program in the os to periodically scan them?
Would an EPROM need UV wiping if you are storing the same code?
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Old 16th May 2020, 6:00 pm   #24
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Default Re: How long can a computer last?

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Originally Posted by Craig Sawyers View Post
Failure of all electrical equipment follows a bathtub failure curve. There is a fast fall initially due to "infant mortality", and after that a long period in the bottom of the bath when failure rate is small, and then a slow rise in failures at end of life.

The stable period failure rate is governed by the Arrhenius equation, which is a chemical rate equation of the form exp(-Ea/kT) where Ea is an "activation energy", and kT is the usual Boltzmann constant and absolute temperature that you find in semiconductor theory.

Anyway, Ea is different for different components. But the general behaviour is that keeping things cool is critical. That is why electrolytic caps fail much quicker at higher temperatures.

See for example https://www.jedec.org/standards-docu...on-reliability

But keep things cool in a computer (or any electronics for that matter) is a good thing for longevity. Periodically open the case and blow dust and grot out (particularly processor and graphics card heatsinks), and clean fan filters is essential maintenance.

But as to long term reliability? Well it is a statistical thing so there is not a hard and fast answer. But keep it cool and clean is a good thing.

Craig
I maintain a computer for a friend, I build it and it's now 12 years old and still going strong, and used daily for Facebook and YouTube, I mainly just use compressed air to clean it out about once a year and by then it needs it! Its used in a dusty environment.
I have only recently needed to add a used old GPU as it used integrated graphics as it was originally specified for word processing email and googling thow using Yahoo then! It does now have a 120gb used sata SSD, that replaced the much older 80gb hard drive from when it was a Pentium 4

Last edited by audion_1908; 16th May 2020 at 6:02 pm. Reason: Missing t
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Old 16th May 2020, 6:04 pm   #25
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Default Re: How long can a computer last?

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Originally Posted by Craig Sawyers View Post
I have experience in space hardware, in which there has to be 100% inspection of solder joints in flight hardware. For that reason ball grid array devices are not allowed.

Reliability in high radiation environments over may years is of course a given.
Would x-rays help?
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Old 16th May 2020, 6:07 pm   #26
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Default Re: How long can a computer last?

Quote:
Originally Posted by jjl View Post
Quote:
Originally Posted by SiriusHardware View Post
I didn't have time to read the document but one factor which uniquely affects computers and computer controlled devices is the longevity of the firmware code - in older devices for example the programmed firmware code may be held in EPROM where the initial programming is performed by forcing a charge (or no charge) into each memory cell.

Over time this charge gradually fades away and it is a matter of when, not if, the firmware will begin to fail as bits gradually return to their unprogrammed state. So one essential bit of maintenance which needs to be performed on equipment with firmware in EPROM is to 'refresh' the EPROM code by over-programming it every few decades. Every time you do that, you reset the 'data fade' clock back to zero. If you have equipment with EPROMs which were programmed forty or more years ago, they may be getting very close to the onset of bit-rot now. You'll put them away working, and then the next time you get them out they'll be dead or going haywire. The internet is a terrific resource here, though - wherever it is possible to read and archive firmware you will generally find that someone, somewhere, has already done it. With the rise of emulation, firmware for home computers of the 8 and 16 bit eras has been especially widely preserved.

Systems with their firmware programmed in MASK ROM or one-time programmable PROM should not be subject to these problems, although there are no doubt other interesting ways in which they can fail.

More modern computers / computer controlled devices will typically have their firmware code stored in 'flash' memory and this, too, may be subject to gradual degeneration of the firmware code over time although with flash still being a relatively recent technology, that will be for the next generation to worry about.

Whereas with discrete EPROMs it was a simple matter to read and back-up the firmware code while it was still working, most microcontrollers are designed to make their internal code difficult for third parties to read out so it would be much harder to refresh the code in those cases.
EPROMs haven't been used much in domestic PCs since the early '90s nor in any system I've been involved with professionally after 1991, but you are correct about them "forgetting" the data programmed into them.
Flash memory is quite similar in construction to EPROM, but there are more recent innovations.
Single bit per cell Flash devices have specified retention times of decades to centuries. This Flash device has a minimum retention time of 20 years and this PIC microcontroller has a typical retention time of 40 years.
Multi bit per cell NAND Flash devices that are used in SSDs, SD cards, USB sticks etc. are likely to be less reliable.

John
I have read the temperature also affects how long modern ssds can retain data, so would these benefit, from being stored and used at low temperatures, and periodic rewriting of all data?
Can ssds be stored in a freezer?

Could the way to go is to use ssds with good firmware and a type that stores the minimum bits per cell so older ssds or enterprise-grade, or to mirror the database half on ssds half on rugged mechanical hard drives, do ruggedized mechanical hard drives make much difference to reliability with lots of vibration?
Would rewriting the data every 20-years be often enough?

Or go more radical, net boot the all the SSD based computers, and have the data copied to them from magnetic tape backup before use if the computer is expected to not be used for a long time?

https://www.ni.com/en-gb/support/doc...endurance.html
Storage Temperature, Max storage duration at end of drive life
(°C)
85, 2 days
80, 4 days
75, 6 days
70, 10 days
65, 18 days
60, 32 days
55, 56 days
50, 104 days
45, 192 days
40, 365 days
35, 1.9 years
30, 3.8 years
25, 7.8 years
20, 16 years
15, 34 years
10, 75 years
75 years for an end of life sdd at 10°C looks good!

Last edited by audion_1908; 16th May 2020 at 6:33 pm. Reason: Missing ,
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Old 16th May 2020, 6:09 pm   #27
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Default Re: How long can a computer last?

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Originally Posted by stevehertz View Post
Surely with computers the issue is not just hardware, but their inability to keep up with up to date apps and stuff? These all require a never ending increase in computing power that old computers just don't have. They become 'outdated', slow and unusable.
Yes, just like a TV22 will not receive digital television broadcasts, a DAC90A will not receive VHF FM broadcasts, a Decola will not play CDs, etc.

I am a somewhat serious computer collector with a couple of hundred machines (not just micros, quite a few PDP11s, a couple of VAXen, Philips minicomputers, etc). Some are 40 years old and still work. I have had to replace ICs in some of them, but I've kept the architecture the same (in other words I might replace a 74xx with a 74LSxx if the circuit can cope with it, but I've not replaced all the innards with an RPi running an emulator). I back up firmware whenever possible (copy-protected microcontrollers, PALs, etc are a PAIN!).

But I do not expect them (or even older PCs) to run the latest programs. They run the software that was current when they were in use.

I have a modern-ish machine to go on the internet, display/print service manuals and data sheets, etc. I do not pretend to understand how it works, I am not able to program it. But I do understand my PDP's, PERQs, HP9830, etc to component level, I understand the CPU microcode. And so on.
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Old 16th May 2020, 6:26 pm   #28
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Default Re: How long can a computer last?

I am intrigued that no one so far has commented about lead free solder. Then this arrived 15 or so years ago I read up on it and found that the military and control systems were allowed to use leaded solder. It was simply more reliable.

I have read numerous threads where people have cooked their motherboard in an oven at140C for a few hours to get the tin solder to reconnect, any others done this?

In the 70's there was a huge amount of discussion about tin dendrites in bipolar PROMs, apparently fixed now, but tin still grows dendrites.

My main work computer is now about 29 years old. A 486-25 with 800MB IDE disc running MS-DOS 5.1. This isn't used so much now but powered on every week or so over that time for an hour or so. Still good, thank goodness, the disc backups I made I can't read for some reason.

Bit like test equipment really, stuff from the 60's still works, no EPROMs though.
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Old 16th May 2020, 6:36 pm   #29
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Default Re: How long can a computer last?

Quote:
Originally Posted by TonyDuell View Post
Quote:
Originally Posted by stevehertz View Post
Surely with computers the issue is not just hardware, but their inability to keep up with up to date apps and stuff? These all require a never ending increase in computing power that old computers just don't have. They become 'outdated', slow and unusable.
Yes, just like a TV22 will not receive digital television broadcasts, a DAC90A will not receive VHF FM broadcasts, a Decola will not play CDs, etc.

I am a somewhat serious computer collector with a couple of hundred machines (not just micros, quite a few PDP11s, a couple of VAXen, Philips minicomputers, etc). Some are 40 years old and still work. I have had to replace ICs in some of them, but I've kept the architecture the same (in other words I might replace a 74xx with a 74LSxx if the circuit can cope with it, but I've not replaced all the innards with an RPi running an emulator). I back up firmware whenever possible (copy-protected microcontrollers, PALs, etc are a PAIN!).

But I do not expect them (or even older PCs) to run the latest programs. They run the software that was current when they were in use.

I have a modern-ish machine to go on the internet, display/print service manuals and data sheets, etc. I do not pretend to understand how it works, I am not able to program it. But I do understand my PDP's, PERQs, HP9830, etc to component level, I understand the CPU microcode. And so on.
That is very cool that you can keep them running, but what if the requirements don't change, like a computer running a power station, factory or an military aircraft carrier or spaceship?
It would be a sad waste to gut a computer and put a Raspberry Pi or equivalent in it.
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Old 16th May 2020, 6:40 pm   #30
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Default Re: How long can a computer last?

If the requirements don't change then a computer will carry on running the programs it always ran.

'Embedded' systems (whether a microprocessor in a bit of test gear or a minicomputer running a power station) are just an example of this.
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Old 16th May 2020, 6:41 pm   #31
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Default Re: How long can a computer last?

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Originally Posted by woodchips View Post
I am intrigued that no one so far has commented about lead free solder. Then this arrived 15 or so years ago I read up on it and found that the military and control systems were allowed to use leaded solder. It was simply more reliable.

I have read numerous threads where people have cooked their motherboard in an oven at140C for a few hours to get the tin solder to reconnect, any others done this?
So I was about to comment on the BGA and you asked the question. Back at some point in the noughties there was a significant issue with BGAs in laptops. My Tosh failed a few weeks out of the extended warranty. Being a media PC it had an NVidia graphics chip that was BGA. The heat cycling and flexing from picking up and putting down caused it to fail. It was a common fault. So a new machine was ordered. Having nothing to lose, I thought I'd see if I could reflow it. This was before the widely used 20 minutes at 190. Since it was a do or die, I personally used a cooks blowtorch and was gobsmacked when it came back to life. It was used as a backup machine for another year before failing again, before it was baked which made it live another 18 months. When it died again I really couldn't be bothered to try again as it was so out of date. That said, the display is currently sat waiting to be turned into a monitor using one of the chinese kits.

Regarding lead free solder, I understand the issue is that lead free solder is way more likely to suffer from tin whiskers. It's 'a bit' inconvenient if some mission critical piece of hardware fails due to a tin whisker, and has to be brought out of orbit for repair. And it has happened. I've seen photos of a tin whisker on a clock crystal that caused the device to be retrieved and return to earth for investigation. Fair enough to allow a bit of lead if it prevents this.
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Old 16th May 2020, 6:49 pm   #32
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Default Re: How long can a computer last?

Quote:
Originally Posted by woodchips View Post
I am intrigued that no one so far has commented about lead free solder. Then this arrived 15 or so years ago I read up on it and found that the military and control systems were allowed to use leaded solder. It was simply more reliable.

I have read numerous threads where people have cooked their motherboard in an oven at140C for a few hours to get the tin solder to reconnect, any others done this?

In the 70's there was a huge amount of discussion about tin dendrites in bipolar PROMs, apparently fixed now, but tin still grows dendrites.

My main work computer is now about 29 years old. A 486-25 with 800MB IDE disc running MS-DOS 5.1. This isn't used so much now but powered on every week or so over that time for an hour or so. Still good, thank goodness, the disc backups I made I can't read for some reason.

Bit like test equipment really, stuff from the 60's still works, no EPROMs though.
Yes I forgot about lead free solder, I tryed it out in my college days and it did not work for me so have stuck with lead tin rosin core solder, I think the lead stops or slows down the tin wiskers, but would a brush down and compressed air in a clean room help every 10 or so years? Or some form of coating?

I have read about old server rooms with layers of abandoned obsolete cabling under the rased floor and the floor panels and supports being made out of zink plated steel forming zink wiskers that eventually grow long enough to snap off and end up frying the computer/server power supplys, and the more it gets disturbed the worse the problem. So no zink plated steel around the computers.

29 year old 486? Would the motherboard be isa only and use through hole TTL chips? If so you may have the most modern computer that can be easily repaired indefinitely using generic TTL chips, thow with a 5v to 3.3v adapter between the CPU and mb an and 5x86 capable of running at 150mhz but depending on your fsb 100 or 133mhz, I would be tempted to do that! What do you use it for?

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Old 16th May 2020, 6:59 pm   #33
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Default Re: How long can a computer last?

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Originally Posted by audion_1908 View Post
...Do they have a parity check or could one be added to detect the start of bit rot on boot? or is it better to add a program in the os to periodically scan them?
Would an EPROM need UV wiping if you are storing the same code?
Reasonable questions.

Traditional EPROMs don't have any kind of inbuilt error checking per se. Once upon a time it used to be common practice to write or print the 16-bit checksum of the data on the EPROM label so that if you suspected a dud EPROM you could read it, the reader would tell you the checksum and if the checksum did not match you knew you had a corrupted EPROM.

Very often the firmware and the 'OS' is one and the same thing and held in EPROM or EEPROM. Yes, you could make the first task of the firmware be to check its own integrity but that relies on the code for the check itself being the last thing to get corrupted.

No, you don't normally need to erase an EPROM before refreshing it as long as the code you are trying to over-programme it with is identical to the code already in it. The programmer will come up with a warning like 'Device is not blank, are you sure you want to proceed?', to which the answer is YES.

If you are certain that the EPROM in question is currently 100% OK, read it, save a copy of the code and stash copies literally everywhere, and only then do you over-programme the original EPROM. if something goes awry, at least then you haven't destroyed what was your only working copy of the code.

As has been said, other programmable devices pose a much greater problem because their code is often intentionally protected from being read, so the premature death of a microcontroller or programmable logic device can spell disaster - you can buy another blank device but the only person likely to have the code that needs to go in it is the manufacturer, who may not be around any more.

I have a third-party Atari ST HDD interface PCB which is unfortunately in this position - one of the GALs has failed, and the manufacturer is long gone. Luckily, as it was the controller and not the HDD which failed, I was able to connect the drive itself to a SCSI card plonked in a Linux PC and make an exact image of it, so at least I have been able to recover the drive contents.

That drive image is now on an SD card which is in a little box which the Atari ST 'thinks' is an original external HDD unit. I would like to get the original unit going again, but I would probably need a whole replacement HDD interface PCB.
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Old 16th May 2020, 7:01 pm   #34
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Default Re: How long can a computer last?

Quote:
Originally Posted by duncanlowe View Post
Quote:
Originally Posted by woodchips View Post
I am intrigued that no one so far has commented about lead free solder. Then this arrived 15 or so years ago I read up on it and found that the military and control systems were allowed to use leaded solder. It was simply more reliable.

I have read numerous threads where people have cooked their motherboard in an oven at140C for a few hours to get the tin solder to reconnect, any others done this?
So I was about to comment on the BGA and you asked the question. Back at some point in the noughties there was a significant issue with BGAs in laptops. My Tosh failed a few weeks out of the extended warranty. Being a media PC it had an NVidia graphics chip that was BGA. The heat cycling and flexing from picking up and putting down caused it to fail. It was a common fault. So a new machine was ordered. Having nothing to lose, I thought I'd see if I could reflow it. This was before the widely used 20 minutes at 190. Since it was a do or die, I personally used a cooks blowtorch and was gobsmacked when it came back to life. It was used as a backup machine for another year before failing again, before it was baked which made it live another 18 months. When it died again I really couldn't be bothered to try again as it was so out of date. That said, the display is currently sat waiting to be turned into a monitor using one of the chinese kits.

Regarding lead free solder, I understand the issue is that lead free solder is way more likely to suffer from tin whiskers. It's 'a bit' inconvenient if some mission critical piece of hardware fails due to a tin whisker, and has to be brought out of orbit for repair. And it has happened. I've seen photos of a tin whisker on a clock crystal that caused the device to be retrieved and return to earth for investigation. Fair enough to allow a bit of lead if it prevents this.
I think lead free solder is more likely to have hidden dry joints as well, and that baking partially fixes.
I can't imagine the baking dose the capacitors much good!

Taking a cooks blowtorch to a laptop GPU to fix it would get a lot of YouTube views now!
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Old 16th May 2020, 7:13 pm   #35
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Default Re: How long can a computer last?

Quote:
Originally Posted by SiriusHardware View Post
Quote:
Originally Posted by audion_1908 View Post
...Do they have a parity check or could one be added to detect the start of bit rot on boot? or is it better to add a program in the os to periodically scan them?
Would an EPROM need UV wiping if you are storing the same code?
Reasonable questions.

Traditional EPROMs don't have any kind of inbuilt error checking per se. Once upon a time it used to be common practice to write or print the 16-bit checksum of the data on the EPROM label so that if you suspected a dud EPROM you could read it, the reader would tell you the checksum and if the checksum did not match you knew you had a corrupted EPROM.

Very often the firmware and the 'OS' is one and the same thing and held in EPROM or EEPROM. Yes, you could make the first task of the firmware be to check its own integrity but that relies on the code for the check itself being the last thing to get corrupted.

No, you don't normally need to erase an EPROM before refreshing it as long as the code you are trying to over-programme it with is identical to the code already in it. The programmer will come up with a warning like 'Device is not blank, are you sure you want to proceed?', to which the answer is YES.

If you are certain that the EPROM in question is currently 100% OK, read it, save a copy of the code and stash copies literally everywhere, and only then do you over-programme the original EPROM. if something goes awry, at least then you haven't destroyed what was your only working copy of the code.

As has been said, other programmable devices pose a much greater problem because their code is often intentionally protected from being read, so the premature death of a microcontroller or programmable logic device can spell disaster - you can buy another blank device but the only person likely to have the code that needs to go in it is the manufacturer, who may not be around any more.

I have a third-party Atari ST HDD interface PCB which is unfortunately in this position - one of the GALs has failed, and the manufacturer is long gone. Luckily, as it was the controller and not the HDD which failed, I was able to connect the drive itself to a SCSI card plonked in a Linux PC and make an exact image of it, so at least I have been able to recover the drive contents.

That drive image is now on an SD card which is in a little box which the Atari ST 'thinks' is an original external HDD unit. I would like to get the original unit going again, but I would probably need a whole replacement HDD interface PCB.
I understand that having the EPROM code check it's own checksum is not fool proof but it could be a good fist line of protection, like old pcs counting and checking its RAM on boot

So copy protection might be my enemy! Protect a company that's long gone!

Also the EPROM burner can do a read verify after burning.

The GAL it's like a small FPGA? Could it be reverse engineered or you get the code from somebody else's good one, maybe somebody on the nets has reverse engineered it?
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Old 16th May 2020, 7:20 pm   #36
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Default Re: How long can a computer last?

Quote:
Originally Posted by TonyDuell View Post
Quote:
Originally Posted by stevehertz View Post
Surely with computers the issue is not just hardware, but their inability to keep up with up to date apps and stuff? These all require a never ending increase in computing power that old computers just don't have. They become 'outdated', slow and unusable.
Yes, just like a TV22 will not receive digital television broadcasts, a DAC90A will not receive VHF FM broadcasts, a Decola will not play CDs, etc.

I am a somewhat serious computer collector with a couple of hundred machines (not just micros, quite a few PDP11s, a couple of VAXen, Philips minicomputers, etc). Some are 40 years old and still work. I have had to replace ICs in some of them, but I've kept the architecture the same (in other words I might replace a 74xx with a 74LSxx if the circuit can cope with it, but I've not replaced all the innards with an RPi running an emulator). I back up firmware whenever possible (copy-protected microcontrollers, PALs, etc are a PAIN!).

But I do not expect them (or even older PCs) to run the latest programs. They run the software that was current when they were in use.

I have a modern-ish machine to go on the internet, display/print service manuals and data sheets, etc. I do not pretend to understand how it works, I am not able to program it. But I do understand my PDP's, PERQs, HP9830, etc to component level, I understand the CPU microcode. And so on.
How do you get round copy-protected microcontrollers, PALs, etc? And how are they copy protected?
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Old 16th May 2020, 7:27 pm   #37
audion_1908
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Default Re: How long can a computer last?

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Originally Posted by SiriusHardware View Post
I didn't have time to read the document but one factor which uniquely affects computers and computer controlled devices is the longevity of the firmware code - in older devices for example the programmed firmware code may be held in EPROM where the initial programming is performed by forcing a charge (or no charge) into each memory cell.

Over time this charge gradually fades away and it is a matter of when, not if, the firmware will begin to fail as bits gradually return to their unprogrammed state. So one essential bit of maintenance which needs to be performed on equipment with firmware in EPROM is to 'refresh' the EPROM code by over-programming it every few decades. Every time you do that, you reset the 'data fade' clock back to zero. If you have equipment with EPROMs which were programmed forty or more years ago, they may be getting very close to the onset of bit-rot now. You'll put them away working, and then the next time you get them out they'll be dead or going haywire. The internet is a terrific resource here, though - wherever it is possible to read and archive firmware you will generally find that someone, somewhere, has already done it. With the rise of emulation, firmware for home computers of the 8 and 16 bit eras has been especially widely preserved.

Systems with their firmware programmed in MASK ROM or one-time programmable PROM should not be subject to these problems, although there are no doubt other interesting ways in which they can fail.

More modern computers / computer controlled devices will typically have their firmware code stored in 'flash' memory and this, too, may be subject to gradual degeneration of the firmware code over time although with flash still being a relatively recent technology, that will be for the next generation to worry about.

Whereas with discrete EPROMs it was a simple matter to read and back-up the firmware code while it was still working, most microcontrollers are designed to make their internal code difficult for third parties to read out so it would be much harder to refresh the code in those cases.
How do they hide the code? And how many times can an eprom or eeprom be rewritten? If once every 20 years it probably won't matter! Lol as long as its atleast 5 that gets you a century!
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Old 16th May 2020, 7:28 pm   #38
audion_1908
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Default Re: How long can a computer last?

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Originally Posted by Craig Sawyers View Post
I have experience in space hardware, in which there has to be 100% inspection of solder joints in flight hardware. For that reason ball grid array devices are not allowed.

Reliability in high radiation environments over may years is of course a given.
How are the solder joints inspected? With a microscope? I would not like that job!
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Old 16th May 2020, 7:36 pm   #39
audion_1908
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Default Re: How long can a computer last?

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Originally Posted by GMB View Post
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I know mechanical parts can be unreliable too, but hard drives can be replaced with SSDs,
SSDs big feature is that they are fast and generally survive being dropped while powered, unlike their mechanical cousins. But all Flash technology intrinsically has a finite life so I am not sure they last longer than hard drives under ideal conditions.

The biggest worry for any microprocessor-based thing is loss of firmware - because apart from the oldest examples, they use EPROM and Flash which have a finite life so are certain to die one day, although the best examples seem to have outlived their specified life expectancy. So make sure you have copies - but that is hard because there is a lot of sneaky firmware like the programming of gate arrays, and some peripherals have their own processors (e.g. modern hard drives).

Very high density chips will enevitably fail due to solid state diffusion - so that's another vote for keeping cool and using older technology. In fact, looking back at my pile of dead PCs I think that is the thing that did for most of them.

A number of very early computers still work because their main worry was tin-whiskers in germanium transistors - but easily replaced, so maintainable. And of course the very early computers came with absolutely everything documented. Wouldn't that be nice?
I know SSD are not perfect, but I think they will be more reliable if you pulled a 40+ year mechanical hard drive and ssd off the parts shelf the SSD is more likely to work, unless bit rot has taken out the firmware! But they are in the same boat.

How long is solid state diffusion likely to take before it starts killing chips? I presume chips with smaller transistors running at higher temperatures are more susceptible. So good cooling over stock, could help.

I know having good documentation makes the difference between a piece of unrepairable junk and an easy fix
I have a basic 10mhz CRT scope that's probably 30 or 40 year's old but I can't find a schematic and it has toasted resistors, and mystery capacitors, so I am stuck on how to fix it, if I had a schematic it would be easy.

I know the IBM XT was fully documented, but how far did it go? where there fully documented TTL only through hole, 486 motherboard?

How do modern hard drives use sneaky firmware?

Last edited by audion_1908; 16th May 2020 at 7:43 pm.
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Old 16th May 2020, 7:45 pm   #40
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Default Re: How long can a computer last?

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Originally Posted by audion_1908 View Post
The GAL it's like a small FPGA? Could it be reverse engineered or you get the code from somebody else's good one, maybe somebody on the nets has reverse engineered it?
Some of that does go on. Not having been involved I don't know how that problem is approached, whether they sometimes 'extract' the underlying code via a process which is not supposed to work - early PICs microcontrollers were apparently susceptible to that sort of attack - or whether it's always just done by analysis of how a (known working) chip responds to external stimuli.

Taking a simple case, GALs are sometimes used as custom address decoders, so that when the value of the address on the data bus is within a certain range, one particular IC or set of ICs on the bus is selected. When the value of the address on the bus is within another range, another IC or set of ICs is selected. Sometimes other lines are involved as well, such as the read data / write data lines.

You can take this chip, use a test circuit or a microcontroller to apply every possible address and control line combination to the inputs of a known good GAL and record the states of the GAL outputs in each case, then, having created a 'truth table' for the GAL, you can recreate the code which needs to go into that type of GAL to make it behave in that way. This of course depends on your having either the original device, still working, or a working one borrowed from another unit, so you can analyse its behaviour.
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