My query

+3 Hamza Nasim · February 29, 2016
What maximum memory can we install on a 32 bit architecture? And what is the maximum upgrade of memory we can have on a 64-bit system? 

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+1 Pere Garau Burguera · February 29, 2016
For 32 bit the maximum is usually 4GB, for 64 bit the maximum is so high you will never get to the limitation, so you can put as much memory as you want.
+2 Perverse Programmer · March 1, 2016
You're talking about a brand ("32 bit architecture") as though you understand it, but you don't... It's just a brand. It's meaningless. People often use it to refer to:


  • The largest unit of memory in a processor, in which case even the Pentiums from 1995 should be considered 128 bit processors

  • The width of the bus (more commonly, the number of traces that the bus contains on the mainboard, this is technically correct), in which case many "64 bit" systems are actually 48 bit systems.

  • The amount of addressable memory, AKA the "address space", which as we shall see isn't necessarily limited by any of the above, though it does seem many mainboard manufacturers limit this to 2TB per drive (which is well below 48 bit, let alone 64 bit).



Do you think the 286 (a "16 bit" processor) was limited to a 16 bit address space? I want some of what you're smoking... It's documented to operate with up to 2MB of RAM, which is 32x greater than if a 16-bit bus were limited to a 16-bit address space. They likely used tricks similar to what they used for hard drives.

This leads me on to another point: You must have been living in a sad world if your 32-bit systems from the ~2000-2006 (and a little beyond that) era were limited to 4GB. It isn't uncommon to discover 20GB (and larger) hard drives in such systems at the dump.

What do we consider "memory"? Does it matter whether it's volatile or non-volatile? Does it matter whether it's installed into DIMMs, or behind a drive controller? Perhaps it's integrated directly into the CPU. As we'll soon find out when primary and secondary memory are merged (I'll give it ten years), no, it doesn't matter. We can treat primary memory as secondary, and vice-versa...

... and the maximum amount of either type of memory has no direct correlation to the "number of bits in the architecture"...
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