System Architecture
Let's study the architecture of modern systems to get a better understanding of how they work.
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Prototypical system architecture
To begin our discussion, let’s look at a “classical” diagram of a typical system, given below.
The picture shows a single CPU attached to the main memory of the system via some kind of memory bus or interconnect. Some devices are connected to the system via a general I/O bus, which in many modern systems would be PCI (or one of its many derivatives); graphics and some other higher-performance I/O devices might be found here. Finally, even lower down are one or more of what we call a peripheral bus, such as SCSI, SATA, or USB. These connect slow devices to the system, including disks, mice, and keyboards.
One question you might ask is: why do we need a hierarchical structure like this? Put simply: physics, and cost. The faster a bus is, the shorter it must be; thus, a high-performance memory bus does not have much room to plug devices and such into it. In addition, engineering a bus for high performance is quite costly. Thus, system designers have adopted this hierarchical approach, where components that demand high performance (such as the graphics card) are nearer the CPU. Lower performance components are further away. The benefits of placing disks and other slow devices on a peripheral bus are manifold; in particular, you can place a large number of devices on it.
Modern system architecture
Of course, modern systems increasingly use specialized chipsets and faster point-to-point interconnects to improve performance. The figure below shows an approximate diagram of
Along the top, the CPU connects most closely to the memory system, but also has a high-performance connection to the graphics card (and thus, the display) to enable gaming (oh, the horror!) and other graphics-intensive applications.
The CPU connects to an I/O chip via Intel’s proprietary DMI (Direct Media Interface), and the rest of the devices connect to this chip via a number of different interconnects. On the right, one or more hard drives connect to the system via the eSATA interface; ATA (the AT Attachment, in reference to providing connection to the IBM PC AT), then SATA (for Serial ATA), and now eSATA (for external SATA) represent an evolution of storage interfaces over the past decades, with each step forward increasing performance to keep pace with modern storage devices.
Below the I/O chip are a number of USB (Universal Serial Bus) connections, which in this depiction enable a keyboard and mouse to be attached to the computer. On many modern systems, USB is used for low-performance devices such as these. Finally, on the left, other higher performance devices can be connected to the system via PCIe (Peripheral Component Interconnect Express). In this diagram, a network interface is attached to the system here; higher performance storage devices (such as NVMe persistent storage devices) are often connected here.
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