How much RAM could one put in a typical 80386 setup?












15















I read on Wikipedia that 80386 could theoretically handle 4GiB of RAM. Knowing how long ago that was, I find it impossible to believe that anyone could actually connect as much to the CPU. So, given the constraints from motherboards and actual RAM chips existing at that time, how much RAM could one put together with an 80386?










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  • Keep in mind that that's the virtual address space, and many operating systems used it to keep nice round numbers for process-space blocks.

    – chrylis
    12 hours ago











  • I'm not claiming to know of any other kind of computer that used the 386, but when you say, "setup," can we assume that you mean, "made-for-Windows PC?"

    – Solomon Slow
    11 hours ago













  • @chrylis The virtual address space of the 386 was 32 bit, but here we are talking about physical pins connected with wires. It is so physical address space, as it only can be.

    – peterh
    5 hours ago











  • @peterh That was directed at the implicit question of "why so much address space if you couldn't possibly add it to the motherboard?"

    – chrylis
    3 hours ago
















15















I read on Wikipedia that 80386 could theoretically handle 4GiB of RAM. Knowing how long ago that was, I find it impossible to believe that anyone could actually connect as much to the CPU. So, given the constraints from motherboards and actual RAM chips existing at that time, how much RAM could one put together with an 80386?










share|improve this question







New contributor




d33tah is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.





















  • Keep in mind that that's the virtual address space, and many operating systems used it to keep nice round numbers for process-space blocks.

    – chrylis
    12 hours ago











  • I'm not claiming to know of any other kind of computer that used the 386, but when you say, "setup," can we assume that you mean, "made-for-Windows PC?"

    – Solomon Slow
    11 hours ago













  • @chrylis The virtual address space of the 386 was 32 bit, but here we are talking about physical pins connected with wires. It is so physical address space, as it only can be.

    – peterh
    5 hours ago











  • @peterh That was directed at the implicit question of "why so much address space if you couldn't possibly add it to the motherboard?"

    – chrylis
    3 hours ago














15












15








15








I read on Wikipedia that 80386 could theoretically handle 4GiB of RAM. Knowing how long ago that was, I find it impossible to believe that anyone could actually connect as much to the CPU. So, given the constraints from motherboards and actual RAM chips existing at that time, how much RAM could one put together with an 80386?










share|improve this question







New contributor




d33tah is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












I read on Wikipedia that 80386 could theoretically handle 4GiB of RAM. Knowing how long ago that was, I find it impossible to believe that anyone could actually connect as much to the CPU. So, given the constraints from motherboards and actual RAM chips existing at that time, how much RAM could one put together with an 80386?







386






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asked 16 hours ago









d33tahd33tah

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1787




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Check out our Code of Conduct.






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Check out our Code of Conduct.













  • Keep in mind that that's the virtual address space, and many operating systems used it to keep nice round numbers for process-space blocks.

    – chrylis
    12 hours ago











  • I'm not claiming to know of any other kind of computer that used the 386, but when you say, "setup," can we assume that you mean, "made-for-Windows PC?"

    – Solomon Slow
    11 hours ago













  • @chrylis The virtual address space of the 386 was 32 bit, but here we are talking about physical pins connected with wires. It is so physical address space, as it only can be.

    – peterh
    5 hours ago











  • @peterh That was directed at the implicit question of "why so much address space if you couldn't possibly add it to the motherboard?"

    – chrylis
    3 hours ago



















  • Keep in mind that that's the virtual address space, and many operating systems used it to keep nice round numbers for process-space blocks.

    – chrylis
    12 hours ago











  • I'm not claiming to know of any other kind of computer that used the 386, but when you say, "setup," can we assume that you mean, "made-for-Windows PC?"

    – Solomon Slow
    11 hours ago













  • @chrylis The virtual address space of the 386 was 32 bit, but here we are talking about physical pins connected with wires. It is so physical address space, as it only can be.

    – peterh
    5 hours ago











  • @peterh That was directed at the implicit question of "why so much address space if you couldn't possibly add it to the motherboard?"

    – chrylis
    3 hours ago

















Keep in mind that that's the virtual address space, and many operating systems used it to keep nice round numbers for process-space blocks.

– chrylis
12 hours ago





Keep in mind that that's the virtual address space, and many operating systems used it to keep nice round numbers for process-space blocks.

– chrylis
12 hours ago













I'm not claiming to know of any other kind of computer that used the 386, but when you say, "setup," can we assume that you mean, "made-for-Windows PC?"

– Solomon Slow
11 hours ago







I'm not claiming to know of any other kind of computer that used the 386, but when you say, "setup," can we assume that you mean, "made-for-Windows PC?"

– Solomon Slow
11 hours ago















@chrylis The virtual address space of the 386 was 32 bit, but here we are talking about physical pins connected with wires. It is so physical address space, as it only can be.

– peterh
5 hours ago





@chrylis The virtual address space of the 386 was 32 bit, but here we are talking about physical pins connected with wires. It is so physical address space, as it only can be.

– peterh
5 hours ago













@peterh That was directed at the implicit question of "why so much address space if you couldn't possibly add it to the motherboard?"

– chrylis
3 hours ago





@peterh That was directed at the implicit question of "why so much address space if you couldn't possibly add it to the motherboard?"

– chrylis
3 hours ago










3 Answers
3






active

oldest

votes


















23














I very much doubt that anyone would ever have seriously considered fitting 4 GiB in a 386-based system, let alone designing such a beast. (To put this into context, I remember seeing early 1 GiB Alpha servers on the factory floor of Digital’s plant in Scotland in 1994, and those machines were priced at around $250,000...)



The Red Hill hardware guide provides a number of examples. 386SX systems were limited to 16 MiB at most anyway, because of the limited number of address lines. For 386DX systems, a common configuration included 8 SIMM slots, for up to 32 MiB of RAM, but Red Hill’s golden oldies page lists one SIPP-based motherboard which might have been usable with 64 MiB. Some manufacturers produced expansion boards to add more memory — e.g. ALR systems had expansion boards supporting up to 48 MiB each. In early 1993, in the US, 4 MiB of RAM cost over $100.



I bought a 386DX/33 in 1992, with 8 MiB of RAM out of a maximum 32 MiB, and that was considered large at the time — enough to run Windows 3.1 or OS/2 very comfortably. I kept that system for four years, eventually switching to Linux, and never needed to add more memory.



In those days, even servers had “small” base configurations as presented in advertisements — see this 1990 ALR advert with a 386/33 and 5 MiB of RAM for a cool $6,290...






share|improve this answer


























  • The limit by address lines is the important factor one could not put 4 GiB memory into a 386 setup. There were practical reasons that beat theory.

    – Bernhard Döbler
    14 hours ago






  • 1





    @Bernhard I’m not sure I understand — are you saying the 386 didn’t have enough address lines for 4 GiB of RAM?

    – Stephen Kitt
    14 hours ago











  • Sorry, I dont want to create confusion. The processors sure had the addresses. I always believed motherboards were not equipped to handle that much memory as it was not needed.

    – Bernhard Döbler
    14 hours ago






  • 1





    Ah, right, yes — adding lines costs money and would only be done if it was useful!

    – Stephen Kitt
    14 hours ago











  • Well, it was obviously Intel 80x86 architecture you were talking about, so just as a side note I remember a tech guy at my uni showing me his fully packed Sparcstation 10 in 1994, which had 512mb, so half of the GB.

    – Gnudiff
    9 hours ago



















14














We can see the datasheet of the 386DX here. The most important part is its pinout.



We have address lines from A2 to A31. It means, that yes, it could have handled 4GB memory on a motherboard. Although it is very unlikely, that any ordinary PC motherboard had been built with the required number of memory sockets at the time.



It is more likely, that it was used at most to make memory-mapped IO easier in embedded environments.1



(A0 and A1 are missing, because the cpu could address only 4byte memory operations. Essentially, it was an only 30-bit CPU, working with 32-bit "bytes". This trick is usual since the early 16-bit era.)



For example, the Weitek Abacus FPU was memory-mapped to 0x0C000000. Floating-point calculations could be done by writing the commands into a 64kB-block starting at far higher as any physical RAM ever could end (at the time... 192MByte), and then reading out the result with mov operands.





enter image description here






share|improve this answer





















  • 1





    Exactly, thanks. It’s worth noting that the 386, while it addressed 32-bit words as you point out, could operate on individual octets by using the bus enable pins (BE0–3).

    – Stephen Kitt
    14 hours ago






  • 1





    Why didn’t they reduce the address pins to a more reasonable number? I mean … nobody expected you to have the full 2^32 bytes of RAM back then, right? A2–A24 for 32MiB RAM should have been perfectly sufficient.

    – Michael
    13 hours ago






  • 1





    Would be fun to see someone fitting a modern 4GiB RAM module via some type of adapter to a real 386 chip and get it to work.

    – Ruslan
    13 hours ago






  • 4





    @Michael I think they had two reasons: 1) they didn't know at the moment, how strongly should they remain compatible with their own CPU sockets of the future. At the time it was yet a real possibility that 586, 686 will be still socket-compatible (or will have at least a socket-compatible version) 2) These CPUs wasn't designed only for PCs, but also for embedded environments. If you access some hardware by memory-mapped IO, it means that you communicate with the chip with memory read/write operations. Essentially, the CPU can see the chip as if it would be a memory module.

    – peterh
    13 hours ago






  • 2





    @Michael The 386SX did that... it narrowed the address bus to 16MB, which was much more realistic in terms of installed RAM. On 386DX hardware, there were also products like the Weitek 1167/3167 FPU's that were memory mapped into addresses way beyond 16MB. (These devices accepted their instruction stream over the address bus, in fact.)

    – mschaef
    12 hours ago



















5














As someone who had a 386, I was happy just to upgrade from 4MB RAM to 8MB RAM. Just think of all the cool things I can do now?! At that point, my motherboard could not contain anymore RAM IC's, so the only way to upgrade further would have been to get denser chips. But by the time I needed more RAM I was on to a 486. Yes, you're correct about the theoretical maximum but, at least for consumer level machines, ain't nobody doin' that.






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  • 1





    My family had a 386sx machine that capped out at 5MB, assuming it was fully populated with 1MB SIMMs (and 1MB was soldered on the motherboard). A few years later, we had a 486 that could go to 32MB if you used 4MB SIMMs, and then to 64MB via a machine-specific memory expansion board. (We never took that machine past 8MB.)

    – mschaef
    12 hours ago











  • IME there were no programs that really needed more than what half of what your RAM could be, for any x86. Modern, "typical", memory-hungry programs are a relatively new invention. If you ever rocked an x86 maxed-out, it was past its service length (and affordable) or doing something atypical.

    – Mazura
    6 hours ago












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3 Answers
3






active

oldest

votes








3 Answers
3






active

oldest

votes









active

oldest

votes






active

oldest

votes









23














I very much doubt that anyone would ever have seriously considered fitting 4 GiB in a 386-based system, let alone designing such a beast. (To put this into context, I remember seeing early 1 GiB Alpha servers on the factory floor of Digital’s plant in Scotland in 1994, and those machines were priced at around $250,000...)



The Red Hill hardware guide provides a number of examples. 386SX systems were limited to 16 MiB at most anyway, because of the limited number of address lines. For 386DX systems, a common configuration included 8 SIMM slots, for up to 32 MiB of RAM, but Red Hill’s golden oldies page lists one SIPP-based motherboard which might have been usable with 64 MiB. Some manufacturers produced expansion boards to add more memory — e.g. ALR systems had expansion boards supporting up to 48 MiB each. In early 1993, in the US, 4 MiB of RAM cost over $100.



I bought a 386DX/33 in 1992, with 8 MiB of RAM out of a maximum 32 MiB, and that was considered large at the time — enough to run Windows 3.1 or OS/2 very comfortably. I kept that system for four years, eventually switching to Linux, and never needed to add more memory.



In those days, even servers had “small” base configurations as presented in advertisements — see this 1990 ALR advert with a 386/33 and 5 MiB of RAM for a cool $6,290...






share|improve this answer


























  • The limit by address lines is the important factor one could not put 4 GiB memory into a 386 setup. There were practical reasons that beat theory.

    – Bernhard Döbler
    14 hours ago






  • 1





    @Bernhard I’m not sure I understand — are you saying the 386 didn’t have enough address lines for 4 GiB of RAM?

    – Stephen Kitt
    14 hours ago











  • Sorry, I dont want to create confusion. The processors sure had the addresses. I always believed motherboards were not equipped to handle that much memory as it was not needed.

    – Bernhard Döbler
    14 hours ago






  • 1





    Ah, right, yes — adding lines costs money and would only be done if it was useful!

    – Stephen Kitt
    14 hours ago











  • Well, it was obviously Intel 80x86 architecture you were talking about, so just as a side note I remember a tech guy at my uni showing me his fully packed Sparcstation 10 in 1994, which had 512mb, so half of the GB.

    – Gnudiff
    9 hours ago
















23














I very much doubt that anyone would ever have seriously considered fitting 4 GiB in a 386-based system, let alone designing such a beast. (To put this into context, I remember seeing early 1 GiB Alpha servers on the factory floor of Digital’s plant in Scotland in 1994, and those machines were priced at around $250,000...)



The Red Hill hardware guide provides a number of examples. 386SX systems were limited to 16 MiB at most anyway, because of the limited number of address lines. For 386DX systems, a common configuration included 8 SIMM slots, for up to 32 MiB of RAM, but Red Hill’s golden oldies page lists one SIPP-based motherboard which might have been usable with 64 MiB. Some manufacturers produced expansion boards to add more memory — e.g. ALR systems had expansion boards supporting up to 48 MiB each. In early 1993, in the US, 4 MiB of RAM cost over $100.



I bought a 386DX/33 in 1992, with 8 MiB of RAM out of a maximum 32 MiB, and that was considered large at the time — enough to run Windows 3.1 or OS/2 very comfortably. I kept that system for four years, eventually switching to Linux, and never needed to add more memory.



In those days, even servers had “small” base configurations as presented in advertisements — see this 1990 ALR advert with a 386/33 and 5 MiB of RAM for a cool $6,290...






share|improve this answer


























  • The limit by address lines is the important factor one could not put 4 GiB memory into a 386 setup. There were practical reasons that beat theory.

    – Bernhard Döbler
    14 hours ago






  • 1





    @Bernhard I’m not sure I understand — are you saying the 386 didn’t have enough address lines for 4 GiB of RAM?

    – Stephen Kitt
    14 hours ago











  • Sorry, I dont want to create confusion. The processors sure had the addresses. I always believed motherboards were not equipped to handle that much memory as it was not needed.

    – Bernhard Döbler
    14 hours ago






  • 1





    Ah, right, yes — adding lines costs money and would only be done if it was useful!

    – Stephen Kitt
    14 hours ago











  • Well, it was obviously Intel 80x86 architecture you were talking about, so just as a side note I remember a tech guy at my uni showing me his fully packed Sparcstation 10 in 1994, which had 512mb, so half of the GB.

    – Gnudiff
    9 hours ago














23












23








23







I very much doubt that anyone would ever have seriously considered fitting 4 GiB in a 386-based system, let alone designing such a beast. (To put this into context, I remember seeing early 1 GiB Alpha servers on the factory floor of Digital’s plant in Scotland in 1994, and those machines were priced at around $250,000...)



The Red Hill hardware guide provides a number of examples. 386SX systems were limited to 16 MiB at most anyway, because of the limited number of address lines. For 386DX systems, a common configuration included 8 SIMM slots, for up to 32 MiB of RAM, but Red Hill’s golden oldies page lists one SIPP-based motherboard which might have been usable with 64 MiB. Some manufacturers produced expansion boards to add more memory — e.g. ALR systems had expansion boards supporting up to 48 MiB each. In early 1993, in the US, 4 MiB of RAM cost over $100.



I bought a 386DX/33 in 1992, with 8 MiB of RAM out of a maximum 32 MiB, and that was considered large at the time — enough to run Windows 3.1 or OS/2 very comfortably. I kept that system for four years, eventually switching to Linux, and never needed to add more memory.



In those days, even servers had “small” base configurations as presented in advertisements — see this 1990 ALR advert with a 386/33 and 5 MiB of RAM for a cool $6,290...






share|improve this answer















I very much doubt that anyone would ever have seriously considered fitting 4 GiB in a 386-based system, let alone designing such a beast. (To put this into context, I remember seeing early 1 GiB Alpha servers on the factory floor of Digital’s plant in Scotland in 1994, and those machines were priced at around $250,000...)



The Red Hill hardware guide provides a number of examples. 386SX systems were limited to 16 MiB at most anyway, because of the limited number of address lines. For 386DX systems, a common configuration included 8 SIMM slots, for up to 32 MiB of RAM, but Red Hill’s golden oldies page lists one SIPP-based motherboard which might have been usable with 64 MiB. Some manufacturers produced expansion boards to add more memory — e.g. ALR systems had expansion boards supporting up to 48 MiB each. In early 1993, in the US, 4 MiB of RAM cost over $100.



I bought a 386DX/33 in 1992, with 8 MiB of RAM out of a maximum 32 MiB, and that was considered large at the time — enough to run Windows 3.1 or OS/2 very comfortably. I kept that system for four years, eventually switching to Linux, and never needed to add more memory.



In those days, even servers had “small” base configurations as presented in advertisements — see this 1990 ALR advert with a 386/33 and 5 MiB of RAM for a cool $6,290...







share|improve this answer














share|improve this answer



share|improve this answer








edited 15 hours ago

























answered 16 hours ago









Stephen KittStephen Kitt

39.3k8160173




39.3k8160173













  • The limit by address lines is the important factor one could not put 4 GiB memory into a 386 setup. There were practical reasons that beat theory.

    – Bernhard Döbler
    14 hours ago






  • 1





    @Bernhard I’m not sure I understand — are you saying the 386 didn’t have enough address lines for 4 GiB of RAM?

    – Stephen Kitt
    14 hours ago











  • Sorry, I dont want to create confusion. The processors sure had the addresses. I always believed motherboards were not equipped to handle that much memory as it was not needed.

    – Bernhard Döbler
    14 hours ago






  • 1





    Ah, right, yes — adding lines costs money and would only be done if it was useful!

    – Stephen Kitt
    14 hours ago











  • Well, it was obviously Intel 80x86 architecture you were talking about, so just as a side note I remember a tech guy at my uni showing me his fully packed Sparcstation 10 in 1994, which had 512mb, so half of the GB.

    – Gnudiff
    9 hours ago



















  • The limit by address lines is the important factor one could not put 4 GiB memory into a 386 setup. There were practical reasons that beat theory.

    – Bernhard Döbler
    14 hours ago






  • 1





    @Bernhard I’m not sure I understand — are you saying the 386 didn’t have enough address lines for 4 GiB of RAM?

    – Stephen Kitt
    14 hours ago











  • Sorry, I dont want to create confusion. The processors sure had the addresses. I always believed motherboards were not equipped to handle that much memory as it was not needed.

    – Bernhard Döbler
    14 hours ago






  • 1





    Ah, right, yes — adding lines costs money and would only be done if it was useful!

    – Stephen Kitt
    14 hours ago











  • Well, it was obviously Intel 80x86 architecture you were talking about, so just as a side note I remember a tech guy at my uni showing me his fully packed Sparcstation 10 in 1994, which had 512mb, so half of the GB.

    – Gnudiff
    9 hours ago

















The limit by address lines is the important factor one could not put 4 GiB memory into a 386 setup. There were practical reasons that beat theory.

– Bernhard Döbler
14 hours ago





The limit by address lines is the important factor one could not put 4 GiB memory into a 386 setup. There were practical reasons that beat theory.

– Bernhard Döbler
14 hours ago




1




1





@Bernhard I’m not sure I understand — are you saying the 386 didn’t have enough address lines for 4 GiB of RAM?

– Stephen Kitt
14 hours ago





@Bernhard I’m not sure I understand — are you saying the 386 didn’t have enough address lines for 4 GiB of RAM?

– Stephen Kitt
14 hours ago













Sorry, I dont want to create confusion. The processors sure had the addresses. I always believed motherboards were not equipped to handle that much memory as it was not needed.

– Bernhard Döbler
14 hours ago





Sorry, I dont want to create confusion. The processors sure had the addresses. I always believed motherboards were not equipped to handle that much memory as it was not needed.

– Bernhard Döbler
14 hours ago




1




1





Ah, right, yes — adding lines costs money and would only be done if it was useful!

– Stephen Kitt
14 hours ago





Ah, right, yes — adding lines costs money and would only be done if it was useful!

– Stephen Kitt
14 hours ago













Well, it was obviously Intel 80x86 architecture you were talking about, so just as a side note I remember a tech guy at my uni showing me his fully packed Sparcstation 10 in 1994, which had 512mb, so half of the GB.

– Gnudiff
9 hours ago





Well, it was obviously Intel 80x86 architecture you were talking about, so just as a side note I remember a tech guy at my uni showing me his fully packed Sparcstation 10 in 1994, which had 512mb, so half of the GB.

– Gnudiff
9 hours ago











14














We can see the datasheet of the 386DX here. The most important part is its pinout.



We have address lines from A2 to A31. It means, that yes, it could have handled 4GB memory on a motherboard. Although it is very unlikely, that any ordinary PC motherboard had been built with the required number of memory sockets at the time.



It is more likely, that it was used at most to make memory-mapped IO easier in embedded environments.1



(A0 and A1 are missing, because the cpu could address only 4byte memory operations. Essentially, it was an only 30-bit CPU, working with 32-bit "bytes". This trick is usual since the early 16-bit era.)



For example, the Weitek Abacus FPU was memory-mapped to 0x0C000000. Floating-point calculations could be done by writing the commands into a 64kB-block starting at far higher as any physical RAM ever could end (at the time... 192MByte), and then reading out the result with mov operands.





enter image description here






share|improve this answer





















  • 1





    Exactly, thanks. It’s worth noting that the 386, while it addressed 32-bit words as you point out, could operate on individual octets by using the bus enable pins (BE0–3).

    – Stephen Kitt
    14 hours ago






  • 1





    Why didn’t they reduce the address pins to a more reasonable number? I mean … nobody expected you to have the full 2^32 bytes of RAM back then, right? A2–A24 for 32MiB RAM should have been perfectly sufficient.

    – Michael
    13 hours ago






  • 1





    Would be fun to see someone fitting a modern 4GiB RAM module via some type of adapter to a real 386 chip and get it to work.

    – Ruslan
    13 hours ago






  • 4





    @Michael I think they had two reasons: 1) they didn't know at the moment, how strongly should they remain compatible with their own CPU sockets of the future. At the time it was yet a real possibility that 586, 686 will be still socket-compatible (or will have at least a socket-compatible version) 2) These CPUs wasn't designed only for PCs, but also for embedded environments. If you access some hardware by memory-mapped IO, it means that you communicate with the chip with memory read/write operations. Essentially, the CPU can see the chip as if it would be a memory module.

    – peterh
    13 hours ago






  • 2





    @Michael The 386SX did that... it narrowed the address bus to 16MB, which was much more realistic in terms of installed RAM. On 386DX hardware, there were also products like the Weitek 1167/3167 FPU's that were memory mapped into addresses way beyond 16MB. (These devices accepted their instruction stream over the address bus, in fact.)

    – mschaef
    12 hours ago
















14














We can see the datasheet of the 386DX here. The most important part is its pinout.



We have address lines from A2 to A31. It means, that yes, it could have handled 4GB memory on a motherboard. Although it is very unlikely, that any ordinary PC motherboard had been built with the required number of memory sockets at the time.



It is more likely, that it was used at most to make memory-mapped IO easier in embedded environments.1



(A0 and A1 are missing, because the cpu could address only 4byte memory operations. Essentially, it was an only 30-bit CPU, working with 32-bit "bytes". This trick is usual since the early 16-bit era.)



For example, the Weitek Abacus FPU was memory-mapped to 0x0C000000. Floating-point calculations could be done by writing the commands into a 64kB-block starting at far higher as any physical RAM ever could end (at the time... 192MByte), and then reading out the result with mov operands.





enter image description here






share|improve this answer





















  • 1





    Exactly, thanks. It’s worth noting that the 386, while it addressed 32-bit words as you point out, could operate on individual octets by using the bus enable pins (BE0–3).

    – Stephen Kitt
    14 hours ago






  • 1





    Why didn’t they reduce the address pins to a more reasonable number? I mean … nobody expected you to have the full 2^32 bytes of RAM back then, right? A2–A24 for 32MiB RAM should have been perfectly sufficient.

    – Michael
    13 hours ago






  • 1





    Would be fun to see someone fitting a modern 4GiB RAM module via some type of adapter to a real 386 chip and get it to work.

    – Ruslan
    13 hours ago






  • 4





    @Michael I think they had two reasons: 1) they didn't know at the moment, how strongly should they remain compatible with their own CPU sockets of the future. At the time it was yet a real possibility that 586, 686 will be still socket-compatible (or will have at least a socket-compatible version) 2) These CPUs wasn't designed only for PCs, but also for embedded environments. If you access some hardware by memory-mapped IO, it means that you communicate with the chip with memory read/write operations. Essentially, the CPU can see the chip as if it would be a memory module.

    – peterh
    13 hours ago






  • 2





    @Michael The 386SX did that... it narrowed the address bus to 16MB, which was much more realistic in terms of installed RAM. On 386DX hardware, there were also products like the Weitek 1167/3167 FPU's that were memory mapped into addresses way beyond 16MB. (These devices accepted their instruction stream over the address bus, in fact.)

    – mschaef
    12 hours ago














14












14








14







We can see the datasheet of the 386DX here. The most important part is its pinout.



We have address lines from A2 to A31. It means, that yes, it could have handled 4GB memory on a motherboard. Although it is very unlikely, that any ordinary PC motherboard had been built with the required number of memory sockets at the time.



It is more likely, that it was used at most to make memory-mapped IO easier in embedded environments.1



(A0 and A1 are missing, because the cpu could address only 4byte memory operations. Essentially, it was an only 30-bit CPU, working with 32-bit "bytes". This trick is usual since the early 16-bit era.)



For example, the Weitek Abacus FPU was memory-mapped to 0x0C000000. Floating-point calculations could be done by writing the commands into a 64kB-block starting at far higher as any physical RAM ever could end (at the time... 192MByte), and then reading out the result with mov operands.





enter image description here






share|improve this answer















We can see the datasheet of the 386DX here. The most important part is its pinout.



We have address lines from A2 to A31. It means, that yes, it could have handled 4GB memory on a motherboard. Although it is very unlikely, that any ordinary PC motherboard had been built with the required number of memory sockets at the time.



It is more likely, that it was used at most to make memory-mapped IO easier in embedded environments.1



(A0 and A1 are missing, because the cpu could address only 4byte memory operations. Essentially, it was an only 30-bit CPU, working with 32-bit "bytes". This trick is usual since the early 16-bit era.)



For example, the Weitek Abacus FPU was memory-mapped to 0x0C000000. Floating-point calculations could be done by writing the commands into a 64kB-block starting at far higher as any physical RAM ever could end (at the time... 192MByte), and then reading out the result with mov operands.





enter image description here







share|improve this answer














share|improve this answer



share|improve this answer








edited 9 hours ago

























answered 14 hours ago









peterhpeterh

551418




551418








  • 1





    Exactly, thanks. It’s worth noting that the 386, while it addressed 32-bit words as you point out, could operate on individual octets by using the bus enable pins (BE0–3).

    – Stephen Kitt
    14 hours ago






  • 1





    Why didn’t they reduce the address pins to a more reasonable number? I mean … nobody expected you to have the full 2^32 bytes of RAM back then, right? A2–A24 for 32MiB RAM should have been perfectly sufficient.

    – Michael
    13 hours ago






  • 1





    Would be fun to see someone fitting a modern 4GiB RAM module via some type of adapter to a real 386 chip and get it to work.

    – Ruslan
    13 hours ago






  • 4





    @Michael I think they had two reasons: 1) they didn't know at the moment, how strongly should they remain compatible with their own CPU sockets of the future. At the time it was yet a real possibility that 586, 686 will be still socket-compatible (or will have at least a socket-compatible version) 2) These CPUs wasn't designed only for PCs, but also for embedded environments. If you access some hardware by memory-mapped IO, it means that you communicate with the chip with memory read/write operations. Essentially, the CPU can see the chip as if it would be a memory module.

    – peterh
    13 hours ago






  • 2





    @Michael The 386SX did that... it narrowed the address bus to 16MB, which was much more realistic in terms of installed RAM. On 386DX hardware, there were also products like the Weitek 1167/3167 FPU's that were memory mapped into addresses way beyond 16MB. (These devices accepted their instruction stream over the address bus, in fact.)

    – mschaef
    12 hours ago














  • 1





    Exactly, thanks. It’s worth noting that the 386, while it addressed 32-bit words as you point out, could operate on individual octets by using the bus enable pins (BE0–3).

    – Stephen Kitt
    14 hours ago






  • 1





    Why didn’t they reduce the address pins to a more reasonable number? I mean … nobody expected you to have the full 2^32 bytes of RAM back then, right? A2–A24 for 32MiB RAM should have been perfectly sufficient.

    – Michael
    13 hours ago






  • 1





    Would be fun to see someone fitting a modern 4GiB RAM module via some type of adapter to a real 386 chip and get it to work.

    – Ruslan
    13 hours ago






  • 4





    @Michael I think they had two reasons: 1) they didn't know at the moment, how strongly should they remain compatible with their own CPU sockets of the future. At the time it was yet a real possibility that 586, 686 will be still socket-compatible (or will have at least a socket-compatible version) 2) These CPUs wasn't designed only for PCs, but also for embedded environments. If you access some hardware by memory-mapped IO, it means that you communicate with the chip with memory read/write operations. Essentially, the CPU can see the chip as if it would be a memory module.

    – peterh
    13 hours ago






  • 2





    @Michael The 386SX did that... it narrowed the address bus to 16MB, which was much more realistic in terms of installed RAM. On 386DX hardware, there were also products like the Weitek 1167/3167 FPU's that were memory mapped into addresses way beyond 16MB. (These devices accepted their instruction stream over the address bus, in fact.)

    – mschaef
    12 hours ago








1




1





Exactly, thanks. It’s worth noting that the 386, while it addressed 32-bit words as you point out, could operate on individual octets by using the bus enable pins (BE0–3).

– Stephen Kitt
14 hours ago





Exactly, thanks. It’s worth noting that the 386, while it addressed 32-bit words as you point out, could operate on individual octets by using the bus enable pins (BE0–3).

– Stephen Kitt
14 hours ago




1




1





Why didn’t they reduce the address pins to a more reasonable number? I mean … nobody expected you to have the full 2^32 bytes of RAM back then, right? A2–A24 for 32MiB RAM should have been perfectly sufficient.

– Michael
13 hours ago





Why didn’t they reduce the address pins to a more reasonable number? I mean … nobody expected you to have the full 2^32 bytes of RAM back then, right? A2–A24 for 32MiB RAM should have been perfectly sufficient.

– Michael
13 hours ago




1




1





Would be fun to see someone fitting a modern 4GiB RAM module via some type of adapter to a real 386 chip and get it to work.

– Ruslan
13 hours ago





Would be fun to see someone fitting a modern 4GiB RAM module via some type of adapter to a real 386 chip and get it to work.

– Ruslan
13 hours ago




4




4





@Michael I think they had two reasons: 1) they didn't know at the moment, how strongly should they remain compatible with their own CPU sockets of the future. At the time it was yet a real possibility that 586, 686 will be still socket-compatible (or will have at least a socket-compatible version) 2) These CPUs wasn't designed only for PCs, but also for embedded environments. If you access some hardware by memory-mapped IO, it means that you communicate with the chip with memory read/write operations. Essentially, the CPU can see the chip as if it would be a memory module.

– peterh
13 hours ago





@Michael I think they had two reasons: 1) they didn't know at the moment, how strongly should they remain compatible with their own CPU sockets of the future. At the time it was yet a real possibility that 586, 686 will be still socket-compatible (or will have at least a socket-compatible version) 2) These CPUs wasn't designed only for PCs, but also for embedded environments. If you access some hardware by memory-mapped IO, it means that you communicate with the chip with memory read/write operations. Essentially, the CPU can see the chip as if it would be a memory module.

– peterh
13 hours ago




2




2





@Michael The 386SX did that... it narrowed the address bus to 16MB, which was much more realistic in terms of installed RAM. On 386DX hardware, there were also products like the Weitek 1167/3167 FPU's that were memory mapped into addresses way beyond 16MB. (These devices accepted their instruction stream over the address bus, in fact.)

– mschaef
12 hours ago





@Michael The 386SX did that... it narrowed the address bus to 16MB, which was much more realistic in terms of installed RAM. On 386DX hardware, there were also products like the Weitek 1167/3167 FPU's that were memory mapped into addresses way beyond 16MB. (These devices accepted their instruction stream over the address bus, in fact.)

– mschaef
12 hours ago











5














As someone who had a 386, I was happy just to upgrade from 4MB RAM to 8MB RAM. Just think of all the cool things I can do now?! At that point, my motherboard could not contain anymore RAM IC's, so the only way to upgrade further would have been to get denser chips. But by the time I needed more RAM I was on to a 486. Yes, you're correct about the theoretical maximum but, at least for consumer level machines, ain't nobody doin' that.






share|improve this answer








New contributor




StealthKK is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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  • 1





    My family had a 386sx machine that capped out at 5MB, assuming it was fully populated with 1MB SIMMs (and 1MB was soldered on the motherboard). A few years later, we had a 486 that could go to 32MB if you used 4MB SIMMs, and then to 64MB via a machine-specific memory expansion board. (We never took that machine past 8MB.)

    – mschaef
    12 hours ago











  • IME there were no programs that really needed more than what half of what your RAM could be, for any x86. Modern, "typical", memory-hungry programs are a relatively new invention. If you ever rocked an x86 maxed-out, it was past its service length (and affordable) or doing something atypical.

    – Mazura
    6 hours ago
















5














As someone who had a 386, I was happy just to upgrade from 4MB RAM to 8MB RAM. Just think of all the cool things I can do now?! At that point, my motherboard could not contain anymore RAM IC's, so the only way to upgrade further would have been to get denser chips. But by the time I needed more RAM I was on to a 486. Yes, you're correct about the theoretical maximum but, at least for consumer level machines, ain't nobody doin' that.






share|improve this answer








New contributor




StealthKK is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
















  • 1





    My family had a 386sx machine that capped out at 5MB, assuming it was fully populated with 1MB SIMMs (and 1MB was soldered on the motherboard). A few years later, we had a 486 that could go to 32MB if you used 4MB SIMMs, and then to 64MB via a machine-specific memory expansion board. (We never took that machine past 8MB.)

    – mschaef
    12 hours ago











  • IME there were no programs that really needed more than what half of what your RAM could be, for any x86. Modern, "typical", memory-hungry programs are a relatively new invention. If you ever rocked an x86 maxed-out, it was past its service length (and affordable) or doing something atypical.

    – Mazura
    6 hours ago














5












5








5







As someone who had a 386, I was happy just to upgrade from 4MB RAM to 8MB RAM. Just think of all the cool things I can do now?! At that point, my motherboard could not contain anymore RAM IC's, so the only way to upgrade further would have been to get denser chips. But by the time I needed more RAM I was on to a 486. Yes, you're correct about the theoretical maximum but, at least for consumer level machines, ain't nobody doin' that.






share|improve this answer








New contributor




StealthKK is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.










As someone who had a 386, I was happy just to upgrade from 4MB RAM to 8MB RAM. Just think of all the cool things I can do now?! At that point, my motherboard could not contain anymore RAM IC's, so the only way to upgrade further would have been to get denser chips. But by the time I needed more RAM I was on to a 486. Yes, you're correct about the theoretical maximum but, at least for consumer level machines, ain't nobody doin' that.







share|improve this answer








New contributor




StealthKK is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|improve this answer



share|improve this answer






New contributor




StealthKK is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









answered 13 hours ago









StealthKKStealthKK

511




511




New contributor




StealthKK is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.





New contributor





StealthKK is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






StealthKK is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.








  • 1





    My family had a 386sx machine that capped out at 5MB, assuming it was fully populated with 1MB SIMMs (and 1MB was soldered on the motherboard). A few years later, we had a 486 that could go to 32MB if you used 4MB SIMMs, and then to 64MB via a machine-specific memory expansion board. (We never took that machine past 8MB.)

    – mschaef
    12 hours ago











  • IME there were no programs that really needed more than what half of what your RAM could be, for any x86. Modern, "typical", memory-hungry programs are a relatively new invention. If you ever rocked an x86 maxed-out, it was past its service length (and affordable) or doing something atypical.

    – Mazura
    6 hours ago














  • 1





    My family had a 386sx machine that capped out at 5MB, assuming it was fully populated with 1MB SIMMs (and 1MB was soldered on the motherboard). A few years later, we had a 486 that could go to 32MB if you used 4MB SIMMs, and then to 64MB via a machine-specific memory expansion board. (We never took that machine past 8MB.)

    – mschaef
    12 hours ago











  • IME there were no programs that really needed more than what half of what your RAM could be, for any x86. Modern, "typical", memory-hungry programs are a relatively new invention. If you ever rocked an x86 maxed-out, it was past its service length (and affordable) or doing something atypical.

    – Mazura
    6 hours ago








1




1





My family had a 386sx machine that capped out at 5MB, assuming it was fully populated with 1MB SIMMs (and 1MB was soldered on the motherboard). A few years later, we had a 486 that could go to 32MB if you used 4MB SIMMs, and then to 64MB via a machine-specific memory expansion board. (We never took that machine past 8MB.)

– mschaef
12 hours ago





My family had a 386sx machine that capped out at 5MB, assuming it was fully populated with 1MB SIMMs (and 1MB was soldered on the motherboard). A few years later, we had a 486 that could go to 32MB if you used 4MB SIMMs, and then to 64MB via a machine-specific memory expansion board. (We never took that machine past 8MB.)

– mschaef
12 hours ago













IME there were no programs that really needed more than what half of what your RAM could be, for any x86. Modern, "typical", memory-hungry programs are a relatively new invention. If you ever rocked an x86 maxed-out, it was past its service length (and affordable) or doing something atypical.

– Mazura
6 hours ago





IME there were no programs that really needed more than what half of what your RAM could be, for any x86. Modern, "typical", memory-hungry programs are a relatively new invention. If you ever rocked an x86 maxed-out, it was past its service length (and affordable) or doing something atypical.

– Mazura
6 hours ago










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