Memory
Memory is like an electronic scratch pad inside the computer. When you launch a program, it is
loaded into and run from memory. Data used by the program is also loaded into memory for fast
access. As new data is entered into the computer, it is also stored in memory-but only
temporarily. The most common type of memory is called random access memory, or RAM.
As a result, the term memory is commonly used to mean RAM. Data is both written to and read
from this memory. (For this reason, RAM is also sometimes called read/write memory.)
Perhaps the most important thing to remember about RAM is that it is volatile, so it needs a
constant supply of power. When you turn off a computer, everything in RAM disappears. Thus,
you should save your data files to a storage device frequently.
One of the most important factors affecting the speed and power of a computer is the amount of
RAM it has. Generally, the more RAM a computer has, the more it can do and the faster it can
perform certain tasks. The most common measurement unit for describing a computer's memory
is the byte—the amount of memory it takes to store a single character, such as a letter of the
alphabet or a numeral. When referring to a computer's memory, the numbers are often so large
that it is helpful to use terms such as kilobyte (KB), megabyte (MB), gigabyte (GB), and
terabyte (TB) to describe the values (see Table 1A.1).
Today's personal computers commonly have at least 256 million bytes of random access memory
(or 256 MB). Many newer systems feature 512 MB or more.
Computers use other types of memory, too. Examples are read-only memory (ROM), which
permanently stores instructions that the computer needs to operate; flash memory, like the kind
used in digital cameras to store images; and cache memory, which helps the CPU retrieve data
and instructions more quickly.
Table 1A.1:Units of Measure for Computer Memory and Storage
Approx. Value Actual Value
Measuring Unit Abbreviation
(bytes) (bytes)
Kilobyte KB 1,000 1,024
1,000,000
Megabyte MB 1,048,576
(1 million)
1,000,000,000
Gigabyte GB 1,073,741,824
(1 billion)
1,000,000,000,000
Terabyte TB 1,099,511,627,776
(1 trillion)
Storage
A computer can function with only processing, memory, input, and output devices. To be really
useful, however, a computer also needs a place to keep program files and related data when they
are not in use. The purpose of storage is to hold data permanently.
You may think of storage as an electronic file cabinet and RAM as an electronic
worktable. When you need to work with a program or a set of data, the computer locates it in
the file cabinet and puts a copy on the table. After you have finished working with the program
or data, you put it back into the file cabinet. The changes you make to data while working on it
replace the original data in the file cabinet (unless you store it in a different place).
Novice computer users often confuse storage with memory. Although the functions of storage
and memory are similar, they work in different ways. There are three major distinctions
between storage and memory:
A. There is more room in storage than in memory, just as there is more room in a file cabinet
than there is on a tabletop.
B. Contents are retained in storage when the computer is turned off, whereas the programs or the
data you put into memory (RAM) disappear when you shut down the computer.
C. Storage is very slow compared to memory, but it is much cheaper than memory.
There are many storage devices; the most common storage medium is the magnetic disk—such
as the hard drive or the old 3.5” floppy disks. Other storage devices include compact discs
CD’s, digital video disk DVD’s, and flash drive memory sticks.
Memory and Storage Questions
1. If you were a salesperson at Best Buy, and customer wanted to buy more memory for
their computer, what would you sell them? RAM or ROM?
2. Why would a person want to buy more memory?
3. How is memory or storage measured? What is the unit of measure? (Inches, pounds,
kilograms?) List three common units of measure.
4. How much memory and storage does a typical 15” laptop computer come with today?
Visit a computer manufacturer like, Dell Computers at http://www.dell.com and record
your findings.
5. Explain the difference between storage and memory.