File Name: bus and memory transfer in computer architecture .zip
A digital system composed of many registers, and paths must be provided to transfer information from one register to another. The number of wires connecting all of the registers will be excessive if separate lines are used between each register and all other registers in the system.
- Direct memory access
- Computer Organization : 2CSE205
- Bus and Memory Transfers
- Registers in Computer Architecture
Direct memory access
A typical digital computer has many register and paths must be provided to transfer information from one register to another. The number of wires will be excessive if seperate lines are used between each register and all other registers in the system. A more efficien scheme for transferring information between registers in a multiple register configuration is a common bus system. A bus structure consists of a set of common lines one for each bit of aregister, through which binary informatio is transferred one at a time.
The multiplexers select the source registre whose binary information is then placed on the bus. A shared communication path consist of one and more lines is called bus and data transfer through this bus is called bus transfer.
What a data read from memory or stored in memory is called memory transfer. When an information is read from memory word is called read operation and data stored in memory is called write operation. The computer has a "bus" where all information travels. It connects all the hardware together. The processor cpu calls for a piece of information and it addresses the bus to find that memory location and retrieve it for the operation that needed it. All of the memory cards are hardware plugged into the bus.
Introduction to the concept of a bus A bus, in computing, is a set of physical connections cables, printed circuits, etc.
The purpose of buses is to reduce the number of "pathways" needed for communication between the components, by carrying out all communications over a single data channel. This is why the metaphor of a "data highway" is sometimes used. If only two hardware components communicate over the line, it is called a hardware port such as aserial port or parallel port. Characteristics of a bus A bus is characterised by the amount of information that can be transmitted at once.
This amount, expressed in bits, corresponds to the number of physical lines over which data is sent simultaneously. A wire ribbon cable can transmit 32 bits in parallel. The term "width" is used to refer to the number of bits that a bus can transmit at once. Additionally, the bus speed is also defined by its frequency expressed in Hertz , the number of data packets sent or received per second.
Each time that data is sent or received is called a cycle. This way, it is possible to find the maximum transfer speed of the bus, the amount of data which it can transport per unit of time, by multiplying its width by its frequency. Bus subassembly In reality, each bus is generally constituted of 50 to distinct physical lines, divided into three subassemblies:.
It is a unidirectional bus. It is a bidirectional bus. It is a bidirectional bus, as it also transmits response signals from the hardware. The internal bus allows the processor to communicate with the system's central memory the RAM. The chipset A chipset is the component which routes data between the computer's buses, so that all the components which make up the computer can communicate with each other.
The chipset originally was made up of a large number of electronic chips, hence the name. The tembridge is generally used to designate a component which connects two buses. It is interesting to note that, in order to communicate, two buses must have the same width. The explains why RAM modules sometimes have to be installed in pairs for example, early Pentium chips, whose processor buses were bit, required two memory modules each 32 bits wide. Here is a table which gives the specifications for the most commonly used buses:.
Depending on the type of memory your chipset and therefore motherboard is designed to handle, the North Bridge runs the memory bus at various speeds. The best solution is if the memory bus runs at the same speed as the processor bus. Running memory at the same speed as the processor bus negates the need for having cache memory on the motherboard. That is why when the L2 cache moved into the processor, nobody added an L3 cache to the motherboard.
However, the most recent high-performance chips, such as the new Pentium Extreme Edition, use only L1 and L2 cache. Thus, it appears that L2 cache will continue to be the most common type of secondary cache for the foreseeable future. The bus and its associated expansion slots are needed because basic systems can't possibly satisfy all the needs of all the people who buy them.
The most basic computer components, such as sound cards and video cards, can be plugged into expansion slots; you also can plug in more specialized devices, such as network interface cards, SCSI host adapters, and others. In most modern PC systems, a variety of basic peripheral devices are built in to the motherboard. Most systems today have at least dual primary and secondary IDE interfaces, four USB ports, a floppy controller, two serial ports, a parallel port, keyboard, and mouse controller built directly into the motherboard.
Many add even more items, such as a built-in sound card, video adapter, SCSI host adapter, network interface or IEEE a port, that also are built in to the motherboard. In essence, even though they are built in, they act as if they were cards plugged into the system's bus slots, including using system resources in the same manner.
Clearly, a better solution is to take the CPU out of the picture entirely, and have the hard disk and system memory communicate directly. Direct memory access or DMA is the generic term used to refer to a transfer protocol where a peripheral device transfers information directly to or from memory, without the system processor being required to perform the transaction.
DMA is discussed in full detail here. The first set of modes are single word DMA modes. There are or were! As I discussed in the page on PIO, maximum transfer rate is double the reciprocal of the specific cycle time for each mode. Obviously, these are not impressive transfer rate numbers by today's standards. Further, performing transfers of a single word at a time is horribly inefficient--each and every transfer requires overhead to set up the transfer.
Here are the multiword DMA transfer modes:. So all DMA accesses today including Ultra DMA are actually multiword; the term "multiword" is now often assumed and no longer specifically mentioned.
The "third party" is the DMA controller. Unfortunately, these DMA controllers are old and very slow--they are basically unchanged since the earliest days of the PC. They are also pretty much tied to the old ISA bus, which was abandoned for hard disk interfaces for performance reasons.
At that point, the old way of doing DMA transfers had to be changed. The term "first party" means that the peripheral device itself does the work of transferring data to and from memory, with no external DMA controller involved. This is also called bus mastering, because when such transfers are occurring the device becomes the "master of the bus". Bus mastering allows the hard disk and memory to work without relying on the old DMA controller built into the system, or needing any support from the CPU.
It requires the use of the PCI bus--older buses like MCA also supported bus mastering but are no longer in common use. Bus-mastering DMA allows for the efficient transfer of data to and from the hard disk and system memory. Interestingly, despite the obvious advantages of bus mastering DMA, the use of bus-mastering multiword DMA mode 2 never really caught on.
There are several reasons for this. The most important was the poor state of support for the technology for the first couple of years. Using PIO required no work and was very simple; DMA was not supported by the first version of Windows 95, so special drivers had to be used. Problems with implementing bus mastering DMA on systems in the to time frame were numerous: issues with buggy drivers, software the didn't work properly, CD-ROM drives that wouldn't work with the drivers, and so on.
In the face of these problems, DMA didn't offer much incentive to make the switch. Given little upside potential, many people including this author stayed away from using DMA, to avoid the compatibility and stability problems that sometimes resulted. Support for DMA was also cleaned up and made native in Windows 9x, and most of the problems with the old drivers were eliminated.
Today, the use of Ultra DMA is the standard in the industry. See here for details on the Ultra DMA modes. What Is a Memory Bus? This section of the chipset also connects directly to the central processing unit and the graphics system. In computing, a bus transfers information from one location to another.
Most modern computers have a large number of buses that cross-connect all sorts of different areas. The northbridge area of the chipset has four main buses.
Each of these busses act independently of one another in most cases. The biggest exception to this is the front side bus and the memory bus. Basic calculations will often sit idle and occupy processor space while they wait for follow-up information. This can create periods of latency, even on a fast computer.
Oddly, more strenuous operations are rarely affected by a slow memory bus, as the time it takes for the processor to compete its operations is often greater than the transferal time. On a technical level, the memory bus is made of two parts. The data bus transfers information between the memory and the chipset. This portion of the bus is often incorrectly referred to as the memory bus, as it does the job most often associated with that part.
The second part of the memory bus is the address bus. The address bus tells the system where information may be stored as it comes into memory and where the information is when it needs to leave memory. The speed of the address bus affects every action on a computer, since all applications need some access to the memory. Regardless of how fast that information comes and goes from the system, it is limited by the speed at which the address bus directs it.
Apparatus for controlling data transfer between a bus and memory array and method for operating same A structure and method of controlling data transfer between a memory and a bus. For write operations, a write buffer is coupled between the bus and the memory array. Data that has been transferred into the write buffer is transferred from the write buffer to the memory array at a faster rate than data is transferred from the bus to the write buffer. For read operations, a read buffer is coupled between the bus and the memory array.
Data is transferred from the memory array to the read buffer at a faster rate than data is transferred from the read buffer to the bus. It is also used forcommunications between the CPU and the processorsupport chipset. Thesize of the processor bus matches the size of the datawords used by CPU.
Computer Organization : 2CSE205
A typical computer has many registers and we need to transfer the information between these registers. A way to transfer the information is using the common bus system. In this article we shall discuss the common bus system using multiplexers. The construction of this bus system for 4 registers is shown above. There are 2 select inputs S0 and S1 which are connected to the select inputs of the multiplexers. The output 1 of register A is connected to input 0 of MUX 1 and similarly other connections are made as shown in the diagram.
BUS. If a computer has 16 registers, each holding 32 bits, how many wires are needed to connect every register to.
Bus and Memory Transfers
We shall study the common bus system of a very basic computer in this article. A basic computer has 8 registers, memory unit and a control unit. The diagram of the common bus system is as shown below. Connections: The outputs of all the registers except the OUTR output register are connected to the common bus.
A Register is a group of flip-flops with each flip-flop capable of storing one bit of information. An n-bit register has a group of n flip-flops and is capable of storing binary information of n-bits. A register consists of a group of flip-flops and gates.
Registers in Computer Architecture
Direct memory access DMA is a feature of computer systems that allows certain hardware subsystems to access main system memory random-access memory independent of the central processing unit CPU. Many hardware systems use DMA, including disk drive controllers, graphics cards , network cards and sound cards. DMA is also used for intra-chip data transfer in multi-core processors. Similarly, a processing element inside a multi-core processor can transfer data to and from its local memory without occupying its processor time, allowing computation and data transfer to proceed in parallel.
If a computer has 16 registers, each holding 32 bits, how many wires are needed to connect every register to every other? A BUS is a single shared set of wires connecting all registers. Bus, 4 8-bit registers connected for input and output. Wire one MUX. Clock speed is limited by the propagation delay through the MUX and wires. Only one register's contents can be on the bus for a given clock cycle. Which of the following are legal?
A typical digital computer has many register and paths must be provided to transfer information from one register to another. The number of wires will be excessive if seperate lines are used between each register and all other registers in the system. A more efficien scheme for transferring information between registers in a multiple register configuration is a common bus system. A bus structure consists of a set of common lines one for each bit of aregister, through which binary informatio is transferred one at a time. The multiplexers select the source registre whose binary information is then placed on the bus.
Tech, M. Common Bus System. While inexpensive, the system must manage its signals carefully, and some parts wait until others finish communicating and relinquish control of the bus.
The basic computer has eight registers , a memory unit, and a control unit. Paths must be provided to transfer information from one register to another and between memory and registers. The number of wires will be excessive if connections are made between the outputs of each register and the inputs of the other registers. A more efficient scheme for transferring information in a system with many registers is to use a common bus.
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