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Explaining Windows Memory Requirements

written by: John Lister•edited by: Christian Cawley•updated: 6/13/2009

Memory is one of the most important factors in running a PC. Here we explore the numbers behind how much memory you need to run different editions of Windows - both in theory and practice.

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    Introductory note

    Explanatory note: There are two types of processor in common use today. Most computers made in the past 15 years had 32-bit processors. 64-bit processors became viable for home computers about five years ago and are now more common than 32-bit in new machines; there are still plenty of 32-bit machines in use though. An operating system like Windows has to be designed in different ways to work with 32-bit and 64-bit machines: XP and Vista are both available in 32-bit and 64-bit editions, as will be Windows 7.

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    Crunching the numbers

    64MB is the bare minimum needed to run XP according to Microsoft.

    128MB is Microsoft’s recommended minimum to run XP.

    700MB is what one tech journalist found was needed simply to run Vista before launching any other applications. (The figures as for XP and other operating systems are much lower.)

    1GB is the bare minimum needed to run Vista according to Microsoft.

    2GB is what Microsoft recently suggested is the right amount of memory for Vista to get “good results, especially for higher knowledge worker scenarios”. That’s been interpreted as an admission that 1GB really isn’t enough for most people running Vista. Many current computers can house up to 2GB memory.

    2GB is also the maximum amount of memory that 32-bit computers can allocate to one program. The 2GB limit isn’t specific to Vista – it’s a simply mathematical limit of a 32-bit system – but it has come to people’s attention with some video games designed for Vista run into problems by hitting this limit. It’s possible to get round this limit, but it’s a complicated process. It’s possible future games may have to be made in 64-bit only editions, which would likely harm sales.

    4GB is the most memory a 32-bit computer can cope with in total. However, when running Vista, only 3 to 3.5 GB of this can actually be used for programs as the rest is reserved for making sure hardware works properly – plus, of course, Vista uses memory itself. Some analysts have questioned whether Windows 7 – which could well require even more memory in practical use – is really going to be suitable for 32-bit machines.

    4GB is also what TechRadar writer Jeremy Laird says is really needed for Vista if you plan to run several programs at once, particularly image or video editing software. He explained this claim by saying that the 700MB needed to run Vista takes up too high a proportion of memory in a 2GB machine. 4GB machines are still relatively rare, though that may change in the next few years.

    8GB is the most memory that can be used by the 64-bit edition of Vista Basic. This is a specific limit placed in Vista.

    16GB is the most memory that can be used by the 64-bit edition of Vista Home Premium, while the remaining editions can use up to 128GB memory. Machines with this amount of memory are not really financially viable for most users, particularly as they often require a special type of motherboard – the PC equivalent of a human skeleton, physically housing the various chips and connecting to the hard drives, DVD drive and so on.

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    The 64-bit edition of WindowsResults from a computer memory scan by