Unformatted text preview: terrupted, it is called volatile storage.
Obviously, a non-volatile storage is desirable. In almost all computer systems, the
primary storage units are volatile and the secondary storage units are non-volatile.
5. Random access. If the time taken to access a piece of data from the storage unit is
independent of the location of the data in the storage unit, it is called a random access
storage or random access memory (RAM). Each separate location of a RAM is as easy to
access as any other location, and takes the same amount of time. In almost all computer
systems, the primary storage units have random access property and the secondary
storage units have either pseudo-random access (access time is nearly same for all
locations but not exactly same) or sequential access (access time directly depends on the
location of the data) property.
Main Memory Organization A primary storage or main memory of a computer system is made up of several small
storage areas called locations or cells. Each of these locations can store a fixed number of
bits called word length of that particular memory. Thus, as shown in Figure 7.3, a given
memory is divided into N words, where N generally is some power of 2. Each word or
"location has a built-in and unique number assigned to it. This number is called the
address of the location and is used to identify the location. Each location can hold either a
data item or an instruction, and its address remains the same regardless of its contents.
The addresses normally start at 0 and the highest address equals the number of words that
can be stored in the memory minus 1. For example, if a memory has 1024 locations, then
th (c) address ranges between 0 and 1023. Thus, at address 0 we find a word, at address 1
a second word, at address 2 a third word, and so on up to the final word at the largest
There is an important difference between the address number and the contents of the
address. A memory is like a large cabinet containing as many drawers as there are
addresses in m...
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This document was uploaded on 04/07/2014.
- Spring '14