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This article mainly introduces "how much GB memory can only be supported by 32-bit windows operating system". In daily operation, I believe many people have doubts about how much GB memory can only be supported by 32-bit windows operating system. Xiaobian consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the question of "how much GB memory can only be supported by 32-bit windows operating system". Next, please follow the editor to study!

Bus structure and composition of motherboard

Speaking of bus, we must be familiar with it, and we must have dealt with it at ordinary times. when we copy data with a USB disk, we have to connect the USB disk to the computer through the USB interface before we can copy it. USB interface is actually a kind of bus, which is generally called USB bus (also known as Universal Serial bus). A long time ago, there was no USB bus. At that time, each peripheral adopted its own interface standard, to cite the simplest example: mouse manufacturers use mouse-specific interfaces, keyboard manufacturers use keyboard-specific interfaces, so PCs have to provide a lot of interfaces, which increases the difficulty and cost of hardware design until the emergence of USB interfaces. It unifies the standards of many peripheral interfaces, which not only makes it easy for users to connect some peripherals, but also enhances the scalability of PC. So now you can see the mouse, keyboard, U disk, printer and other peripherals can be directly plugged into the computer through the USB interface.

Bus is a very important concept in computer system. It is because of bus that all components can work together and work together. In the PC a long time ago, the three-bus structure was adopted, that is, data bus, address bus and control bus. They are used to transmit different types of data, the data bus is used to transmit data, the address bus is used to transmit addresses, and the control bus is used to transmit some control signals. The following picture clearly shows the three-bus structure:

With the development of the times, this simple bus structure has been gradually eliminated. The following picture shows the structure used in modern computing:

In fact, this is also the structure adopted by the modern motherboard, of course, some places may be slightly different (the general structure is similar), friends who have carefully observed the composition of the motherboard may be familiar with the picture above. There are two main parts on the motherboard: North Bridge (North Bridge also known as Host Bridge) and South Bridge (South Bridge). The north bridge is mainly responsible for the data transmission of CPU, memory and graphics cards, while the south bridge is mainly responsible for the communication between the Icano equipment, external storage devices and BIOS. Now some motherboards no longer have the North Bridge, because the chip manufacturers have integrated the functions of the North Bridge directly into the CPU (but let's discuss the model of the sub-image above).

In the above sub-figure, I did not draw the data bus and address bus, etc., because they are integrated in some bus standards, for example, in the PCI bus, the address bus and the data bus are always time-sharing multiplexed (that is, if the PCI bus has a 32-bit data bus, the 32-bit bus can act as the data bus at one time and the address bus at the next). Some buses provide both data bus and address bus.

Let's talk about the functions of several major buses and north-south bridges:

FSB bus: that is, the front-end bus (Front Side Bus), the bridge between CPU and North Bridge, all the data transmitted by CPU and North Bridge must pass through FSB bus. It can be said that the frequency of FSB bus directly affects the speed of CPU accessing memory.

North Bridge: North Bridge is the only bridge for data exchange between CPU and memory, graphics cards and other components, which means that if CPU wants to communicate with any other parts, it must go through the North Bridge. Northbridge chips are usually integrated with memory controllers, which are used to control the communication with memory. Now the north bridge can no longer be seen on the motherboard, and its functions have been integrated into CPU.

PCI bus: PCI bus is a high-performance local bus, which is not limited by CPU and constitutes a high-speed channel between CPU and peripherals. For example, today's graphics cards generally use PCI slots, PCI bus transmission speed is fast, can well let the video card and CPU data exchange.

Nanqiao: it is mainly responsible for the communication between Iamp O devices. If CPU wants to access peripherals, it must go through Nanqiao chip.

With these basics in mind, let's explain why 32-bit systems support up to 4GB memory.

Origin

When using a computer, the maximum supported memory is determined by both the operating system and hardware.

First of all, let's talk about the hardware factors. the address bus has been mentioned above. the number of CPU address buses in the computer determines the addressing range of the CPU. The address corresponding to the address bus is called the physical address. If CPU has 32 address buses (generally 32-bit CPU address bus is 32-bit, and some 32-bit CPU address buses are 36-bit, for example, CPU used as a server), then the addressable physical address range provided is 232=4GB (note here that 32-bit CPU and 64-bit CPU refer to the data width that CPU can handle at a time, that is, bit width, not the number of address buses). Since the advent of 64-bit CPU, 64-bit data can be processed at one time, and its address bus usually uses 36-bit or 40-bit (that is, the physical address space that CPU can address is 64GB or 1T). When CPU accesses any other parts, it needs an address, just like a courier delivers a courier, he doesn't know where to deliver without an address. For example, if CPU wants to read data from a video memory unit, it must know the actual physical address of the video memory cell to be read. Similarly, reading data from the memory cell on the memory bar also needs to know the physical address of the memory unit. In other words, any storage unit that CPU accesses must know its physical address.

The maximum memory that a user can access when using a computer is determined not only by the number of bits of the CPU address bus, but also by the implementation of the operating system. In fact, when the user is using the computer, the address accessed by the process is a logical address, not a real physical address. This logical address is provided by the operating system. CPU needs to transform the logical address of the instruction into a physical address before reading or writing data to the corresponding storage unit (note that the logical address and the physical address correspond to each other).

For the 32-bit windows operating system, the number of address bits used for logical address coding is 32 bits, then the logical address addressing range provided by the operating system is 4GB, while under the intel x86 architecture, the memory mapping technology (Memory-Mapped MMIO) is adopted, that is to say, a part of the 4GB logical address should be divided and mapped with the physical addresses of BIOS ROM, CPU registers and IAMO devices. Then there must be no 4GB in the space in which the logical address can be mapped to the physical address of the memory stick. Just take a look at the following figure:

So when we install a 32-bit windows operating system, even if we buy a 4GB stick of memory, what can actually be accessed by the operating system is definitely less than 4GB, generally around 3.2GB. If the number of address bus bits does not have 32 bits, say 20 bits, then CPU can address to the physical address space of 1MB. Even if the operating system can support the logical address space of 4GB and assume that the memory strip is 4GB, the space that can be accessed by users will not be larger than 1MB (virtual memory technology is not considered here, of course). Therefore, the maximum memory space that users can access is determined by both the hardware and the operating system, both of which are restricted.

For 64-bit operating systems, the number of address bits used for logical address coding is 40 bits, which can support a maximum logical address space of 1T. Consider a situation, if the CPU is 64-bit, the number of address bus bits is 40 bits, the operating system is also 64-bit, the number of address bits used for logical address coding is also 40 bits, and the size of the memory strip is 64GB, can all the 64GB of the memory strip be utilized? The answer is not necessarily, because there is also a factor to consider is the memory controller, the memory controller is located in the North Bridge (now basically in the CPU), the actual address line of the memory controller determines the amount of memory that can be supported, that is to say, if there is no 40-bit address line between the memory controller and the memory slot, it is impossible to make full use of the storage space of the memory bar of 64GB. Of course, there is almost no need to think about memory controllers, because most memory controllers now use at least a 40-bit address bus.

At this point, the study on "how much GB memory a 32-bit windows operating system can only support" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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