CST8174_Lecture_9_Introduction to transfer modes

CST8174_Lecture_9_Introduction to transfer modes -...

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May 11, 2009 Matthew O’ Meara Algonquin College CST8174 CST8174 Computer Technology Basics Transferring Data
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May 11, 2009 Matthew O’ Meara Algonquin College CST8174 Transferring Data All ATA devices transfer data by using a standardized protocol There are two methods of transferring data over the ATA interface PIO modes DMA modes
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May 11, 2009 Matthew O’ Meara Algonquin College CST8174 PIO Programmable Input/Output PIO is the oldest method of transferring data over the ATA interface The CPU as well as the supporting hardware directly controlled the transfer of data between the system and the hard drive This technique had a lot of wasteful overhead as the CPU had a lot of involvement with read/write operations
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May 11, 2009 Matthew O’ Meara Algonquin College CST8174 PIO Modes There are five different PIO modes Cycle time represents how many nanoseconds it takes for each transfer to occur PIO Mode Cycle Time (ns) Transfer Rate (MBps) 0 600 3.3 1 383 5.2 2 240 8.3 3 180 11.1 4 120 16.7
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May 11, 2009 Matthew O’ Meara Algonquin College CST8174 DMA Direct Memory Access Allows the hard drive to transfer data to and from memory directly Huge performance increase over PIO Data transfer occurs independent of the CPU Allows CPU to process other instructions instead of waiting for data transfer DMA transfers can be either 16-bits (single word) or 32-bits (double word) wide
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CST8174_Lecture_9_Introduction to transfer modes -...

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