Computer Buses
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In this video I will
In this video I will look at the buses that are used inside a computer. A bus is a communication pathway that allows data to travel between different components inside a computer. Understanding how buses work will give you a better understanding of what you can achieve with a computer. This will help you determine where potential bottlenecks in system performance may occur when the computer is put under load.
Download the PDF handout: http://itfreetraining.com/handouts/ap...
What is a Bus?
0:23 To start with, let’s consider the question what is a computer bus or as it’s better known, a system bus? A bus inside a computer is essentially a group of electrical wires that carry a signal. On a motherboard, these wires are called traces.
The bus carries data, but you need to control the movement of the data and determine where it is going.
In order to do this, a typical system bus is divided into three parts. The first part is the data bus. This bus carries the data. A computer bus works just like a regular bus used to carry people. The regular bus will have a limited number of seats. A system bus will have a limited number of bits it can send at once. For example, a 32-bit bus can send 32 bits at once. Think of it like a bus with 32 seats and, in order for the bus to leave, it needs to have all 32 seats occupied. A 32-bit bus always sends 32 bits of data at once, no more, no less.
The next step is that the data needs to know where it is going. This is achieved by using the address bus. The address bus essentially tells the computer where the data is going. For example, going to the main memory or to memory on a device. More on that later in the video.
Lastly, there is the control bus. The control bus determines when data is sent. Without any control the computer would not be able to determine when data is sent and when it is complete. Previous data would get mixed up with new data and thus transfer errors would occur.
Simple Bus Example
2:04 To understand the bus better, let’s consider a simple example of how a bus may work. In the old days of computing this is how buses worked. Later in the video, we will see the problems with using a bus designed like this and how modern buses work differently to overcome these problems.
To start with, let’s consider there are 16 wires for the address bus. This will allow us to access 64 kilobytes of memory, not a lot by today’s standards. Now let’s consider that we have a 16-bit data bus. 16 bits can be sent or received on the data bus at once, which is two bytes.
Lastly, we have our control bus. In this example there are only four wires. This is a simple example and you would generally have more. But for this example, there is a read, write, transfer acknowledgment and a clock signal wire.
The clock signal will determine when data is sent. The read and write wires determine if data is being sent and received and the transfer acknowledgment wire determines if the data went through o.k. So essentially, set the address bus to the address you want to read or write to, place or receive your data on the data bus and use the control wires to determine when to start the transfer, what sort of transfer, be it either read or write and if it was received.
This is a very simple example that you may find in a very old computer, but it is not without its problems. Consider that with this example we have 36 wires. Consider now that we wanted to send 32 or 64 bits at once. This would greatly increase the number of wires required, however having extra wires is not the only problem this would create.
Serial vs Parallel
3:52 This brings us to the topic of serial versus parallel. Serial transmission is when data is transferred using one channel. Each bit follows the previous bit, as in ‘follow the leader’. Parallel is when multiple channels are used at the same time. Think of it like line dancing, where everyone is in a line and dancing in sync with each other
Description to long for YouTube. Please see the following link for the rest of the description. http://itfreetraining.com/ap/1b75
References
“The Official CompTIA A+ Core Study Guide (Exam 220-1001)” Chapter 3 position 6269-6554, 7999-8198
“CompTIA A+ Certification Exam Guide Ninth Edition” pages 240-243
“Bus (computing)” https://en.wikipedia.org/wiki/Bus_(co...)
“Address bus” https://en.wikipedia.org/wiki/Address...
“Control Bus” https://en.wikipedia.org/wiki/Control...
“Wait state” https://en.wikipedia.org/wiki/Wait_state
“Fun and Easy PCIE - How the PCI Express Protocol works” Fun and Easy PCIE - How the PCI Expre...
“Picture PCI Express” https://de.wikipedia.org/wiki/Datei:P...
Credits
Trainer: Austin Mason http://ITFreeTraining.com
Voice Talent: HP Lewis http://hplewis.com
Quality Assurance: Brett Batson http://www.pbb-proofreading.uk
Download the PDF handout: http://itfreetraining.com/handouts/ap...
What is a Bus?
0:23 To start with, let’s consider the question what is a computer bus or as it’s better known, a system bus? A bus inside a computer is essentially a group of electrical wires that carry a signal. On a motherboard, these wires are called traces.
The bus carries data, but you need to control the movement of the data and determine where it is going.
In order to do this, a typical system bus is divided into three parts. The first part is the data bus. This bus carries the data. A computer bus works just like a regular bus used to carry people. The regular bus will have a limited number of seats. A system bus will have a limited number of bits it can send at once. For example, a 32-bit bus can send 32 bits at once. Think of it like a bus with 32 seats and, in order for the bus to leave, it needs to have all 32 seats occupied. A 32-bit bus always sends 32 bits of data at once, no more, no less.
The next step is that the data needs to know where it is going. This is achieved by using the address bus. The address bus essentially tells the computer where the data is going. For example, going to the main memory or to memory on a device. More on that later in the video.
Lastly, there is the control bus. The control bus determines when data is sent. Without any control the computer would not be able to determine when data is sent and when it is complete. Previous data would get mixed up with new data and thus transfer errors would occur.
Simple Bus Example
2:04 To understand the bus better, let’s consider a simple example of how a bus may work. In the old days of computing this is how buses worked. Later in the video, we will see the problems with using a bus designed like this and how modern buses work differently to overcome these problems.
To start with, let’s consider there are 16 wires for the address bus. This will allow us to access 64 kilobytes of memory, not a lot by today’s standards. Now let’s consider that we have a 16-bit data bus. 16 bits can be sent or received on the data bus at once, which is two bytes.
Lastly, we have our control bus. In this example there are only four wires. This is a simple example and you would generally have more. But for this example, there is a read, write, transfer acknowledgment and a clock signal wire.
The clock signal will determine when data is sent. The read and write wires determine if data is being sent and received and the transfer acknowledgment wire determines if the data went through o.k. So essentially, set the address bus to the address you want to read or write to, place or receive your data on the data bus and use the control wires to determine when to start the transfer, what sort of transfer, be it either read or write and if it was received.
This is a very simple example that you may find in a very old computer, but it is not without its problems. Consider that with this example we have 36 wires. Consider now that we wanted to send 32 or 64 bits at once. This would greatly increase the number of wires required, however having extra wires is not the only problem this would create.
Serial vs Parallel
3:52 This brings us to the topic of serial versus parallel. Serial transmission is when data is transferred using one channel. Each bit follows the previous bit, as in ‘follow the leader’. Parallel is when multiple channels are used at the same time. Think of it like line dancing, where everyone is in a line and dancing in sync with each other
Description to long for YouTube. Please see the following link for the rest of the description. http://itfreetraining.com/ap/1b75
References
“The Official CompTIA A+ Core Study Guide (Exam 220-1001)” Chapter 3 position 6269-6554, 7999-8198
“CompTIA A+ Certification Exam Guide Ninth Edition” pages 240-243
“Bus (computing)” https://en.wikipedia.org/wiki/Bus_(co...)
“Address bus” https://en.wikipedia.org/wiki/Address...
“Control Bus” https://en.wikipedia.org/wiki/Control...
“Wait state” https://en.wikipedia.org/wiki/Wait_state
“Fun and Easy PCIE - How the PCI Express Protocol works” Fun and Easy PCIE - How the PCI Expre...
“Picture PCI Express” https://de.wikipedia.org/wiki/Datei:P...
Credits
Trainer: Austin Mason http://ITFreeTraining.com
Voice Talent: HP Lewis http://hplewis.com
Quality Assurance: Brett Batson http://www.pbb-proofreading.uk
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