Figure 1-5.Semiconductor memory chip exposed.
Some of the advantages of semiconductor storage
are fast internal processing speeds, high reliability, low
power consumption, high density (many circuits), and
low cost. However, a drawback to this type of storage is
that it must have a constant power source. The term for
this is volatile storage. An example of volatile storage is
RAM. When you turn the power to the computer off, all
the stored data is lost. Also, when there is a power
failure and you do not have a backup power supply, all
the stored data is lost. As mentioned, this is not the case
with magnetic core storage. With core storage, the data
is retained even when there is a power failure or
breakdown, since data is stored in cores in the form of
magnetic charges, not electric current.
BUBBLE STORAGE. Bubble memory is one of
the newer storage technologies, generally used in
laptops. It consists of a very thin crystal made of
semiconductor material. The molecules of the crystal
act as tiny magnets.
Data is stored by changing the
polarity of these molecules, called magnetic domains.
The magnetic domains can be switched in an opposite
direction by passing a current through a control circuit
imprinted on top of the crystal. Like magnetic core
storage, bubble memory is nonvolatile. The data is
retained even when the power is turned off or there is a
power failure. Unlike magnetic storage, reading from
bubble memory is nondestructive. The data does not
have to be regenerated; it is still present after being read.
If we were to view these magnetic domains under a
microscope, they would look like tiny bubbles; hence,
the name, bubble memory. (See figure 1-6.)
Memory Types by Function
Functionally, we can classify memory by its
operational features: random-access memory (RAM),
Figure 1-6.Bubble memory.