ENVS 1000 Lecture Notes - Lecture 17: Industry Standard Architecture, Conventional Pci, Usb
10 May 2018
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ENVS 1000 Tutorial 17 Notes – Actual Direct
Introduction
• Although the illustration implies that these pathways represent actual direct
connections between the various component blocks, this is not actually true.
• The connections could be direct or they could be electronic switches that provide the
connections at the time they are required.
• For example, memory and the I/O modules could each be attached to different buses
that are connected together when DMA takes place.
• The I/O module could be attached by separate connections both to memory and to the
CPU.
• These differences constitute different computer system architectures, representing
different vendors, different goals, and different design philosophies.
• In nearly every system, one or more buses form the backbone for connection of the
various components, memory and I/O, to the CPU.
• In simplest form, a single system bus could connect the CPU to memory and to all the
various modules that control I/O devices.
• Of course this approach would subject the overall performance of the system to the
limited bandwidth of a single bus.
• More commonly, the system bus in bus architecture connects through one or more bus
interface circuits to a number of different interconnected buses.
• A more realistic general bus interface configuration is shown
• The bus organization of a PC, for example, often consists of the system bus, a video
display bus, a PCI-Express and/or PCI bus.
• A serial or parallel ATA bus for the disk drives, probably a Universal Serial Bus, and
sometimes an ISA bus or other buses.
• The system bus, which is the primary interface with the CPU, is sometimes referred to as
the front side bus (FSB).
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