Chap : Interfacing processors and peripherals

8.1 Introduction
- I/O can have a significant impact on system performance
- In some cases, we care more about throughput than latency

8.2 I/O performance measures:
- Assessment of an I/O system must take into account a variety of factors, including performance
- Three benchmarks for determining the performance of disk systems are presented

8.3 Tyeos and characteristics of I/O devices
- There is a wide diversity of I/O devices
- Detailed characteristics of mice, disk drives and networks are presented

8.4 Buses

- A Bus is a shared communication link that uses one set of wires to connect multiple subsystems. 
- There are two important bus protocols: sychronous and asynchronous
- Bus arbitration is required to determine who will get the bus
- Different bus characteristics allow the creation of buses optimized for a wide range of different devices

8.5 Interfacing I/O devices to the memory, processor and the operating system
- Processor-to-device communication is accomplished using memory-mapped I/O or special instructions
- Device-to-procesor communication is accomplished using polling or interrupts
- DMA provides an alternative means of transferring data between I/O devices and the processor

8.6 Designing an I/O System
- Designing an I/O system with latency constraint requires designers to determine latency using one of two techniques (queueing theory or simulation) that are not described in the text
- Designing an I/O system with bandwidth constraints requires the use of a methodology based upon finding the weakest link in the I/O system

8.7 Real Stuff: A typical desktop I/O system
- Two dominant standards in the desktop personal computer market (PCI and SCSI) have led to an enormous degree of commonality among I/O systems

8.8 Fallacies and Pitfalls
- Fallacy: A 100 MB/s bus can transfer 100 MB of data in 1 s
- Pitfall: Using the peak transfer rate of a portion of the I/O system to make performance projections or comparisons
- Fallacy: Magnetic storage is on its last legs and will be replaced shortly
- Pitfall: Moving functions from the CPU to the I/O processor, expecting to improve performance without careful analysis