Unit 7: Storage and I/O
In this unit, we will discuss the input/output devices that enable communication between computers and the outside world in some form. The reliability of these devices is important; we will accordingly discuss the related issues of dependability, availability, and reliability. You will also take a look at non-volatile storage mediums, such as disk and flash memory, before learning about mechanisms used to connect the computer to input/output devices. This unit will conclude by discussing disk system performance measures.
Completing this unit should take you approximately 3 hours.
Upon successful completion of this unit, you will be able to:
- calculate the performance of a synchronous bus vs. an asynchronous bus;
- calculate the bandwidth of a synchronous bus using a given block size; and
- discuss storage and I/O devices, their performance measurement, and RAID technology.
7.1: I/O Devices
Watch this lecture, which discusses the basic ideas behind the input/output (I/O) subsystem of a computer system. The lecturer also looks into performance measurement for I/O devices and interfaces used to interconnect I/O devices to the processor. This is the first of two video lectures on I/O. A computer subsystem consists of three major components: processor, memory, and connections. The key words in the previous sentence are subsystem and connections. To be useful, a computer system needs to have connections with external devices to get data and control signals into the computer and to put data and control signals out. The external devices can be other systems or other systems may be connected to the same devices. Thus, our computer system is part of a network of a few or many other subsystems interconnected to perform useful tasks. We are always interested in how well a task is performed, in terms of time, capacity, and cost. In considering performance relative to our useful task, we have to consider processor performance, memory performance, and the performance of the connections, including the performance of the external devices. This first video lecture looks at external or peripheral devices and I/O performance. Next, we will discuss interfaces, buses, and I/O transfer.
7.2: Connecting I/O Devices to the Processor
- Watch this lecture for an introduction to the interconnection schemes used for the input/output (I/O) subsystem of a computer system. This is the second of two lectures on I/O devices. The previous lecture looked at the connection of memory, either cache or main memory, with peripheral devices and the transfer and transformation of data between them. This video lecture analyzes alternative interconnection schemes with a focus on buses. Also, it discusses protocols for the data that flows on the buses: asynchronous and synchronous. A synchronous protocol uses a clock to time sequence the information flow. An asynchronous protocol does not use a clock; the signal carries the sequencing information. Then, the lecture shows a performance comparison of two different protocols.
Be aware that the last example on this resource has an error. When finding the BW, it says 256 x 4 x 1/14400. It should be 256 x 8 x 1/14400. A byte is 8 bits.
7.3: Measuring Disk Performance
Read this article. Disks have various characteristics, which determine quality attributes, such as reliability, performance, etc. Here, we are interested in performance. Think of some characteristics that affect performance. How can performance of a disk be measured?
7.4: Redundant Array of Inexpensive Disks (RAID)
This article will provide you with a description of RAID technology and will introduce you to techniques that are used for studying performance and reliability in general.
Unit 7 Assessment
- Receive a grade
Take this assessment to see how well you understood this unit.
- This assessment does not count towards your grade. It is just for practice!
- You will see the correct answers when you submit your answers. Use this to help you study for the final exam!
- You can take this assessment as many times as you want, whenever you want.