This chapter begins with generic discussion of storage devices, which it means as a category that covers all the media covered in the chapter. A storage device of any sort, we are told, must have a read/write mechanism and a storage medium.
The chapter gives us a list of characteristics that separate storage devices from each other. The two most important are speed and volatility.
Speed refers to the speed with which a device can be used. The text gives us an example of a processor with a 1 GHz clock rate, and remarks that it would be best to use storage devices that can supply new instructions at that rate. Otherwise, the storage devices introduce wait states for the processor. In general, there is no wait for anything already stored in a register, a short wait for anything stored in RAM, and a longer wait for any other kind of storage. The text discusses the fact that access time is the same for all addresses in RAM, but it can vary from one part of a hard drive to another.
We see a short exercise at the bottom on page 160, showing us a method for calculating the data transfer rate for a de-ice. The calculation is done by taking the inverse of the access time of the device and multiplying it by the word size of the device in bytes.
Volatility has to do with loss of data over time. It is usually related to whether a device needs to be powered in order to retain its data. As I have stated earlier in the notes, the text tells us that primary storage is generally volatile, and secondary storage is generally nonvolatile. It also tells us that devices tend to suffer from a decay of their stored data over time, which makes them all somewhat volatile if they are kept around long enough.
The text continues with a discussion of three access methods that might be used, regardless of the type of storage device:
The text also discusses portability and the relationship between cost and capacity. It should be obvious to anyone who has purchased system components that they cost more the more they can do. Portability is in the eye of the beholder. If we can put a component in a machine, we can take it back out.
The text amplifies on its thoughts about primary storage for a few pages. It classes RAM in two main groups, and a variation:
The text also discusses a few types of nonvolatile memory (NVM). The reader may be familiar with ROM (read only memory) and EEPROM (electronically erasable programmable ROM). These are often used for functions on a motherboard. The text also mentions flash RAM, most often used in memory sticks.
The text discusses several features of hard drives and magnetic tape that have already been mentioned.
The text mentions some facts about solid state drives on page 183. They are better for causing fewer wait states, but still cost a great deal more than hard drives of comparable storage capacity.
The chapter ends with a discussion of optical storage devices, which are read with reflected laser light. The basic information is summarized on page 190:
many things that happen in the Central Processing Unit of a computer. First, we are reminded that a CPU will contain at least three components: the Arithmetic Logic Unit (which does the computation and comparisons), the Control Unit (which moves data and instructions to and from secondary storage, RAM, and registers), and registers (volatile memory in the CPU itself).
The chapter spends the next several pages discussing
electronic notation and physical factors that affect all electrical
equipment, such as heat, electrical resistance, and circuit length. It
also discusses some possible improvements in computing that have in
fact been discussed for years but have yet to be realized.