Computer Memory Works
memory is technically any form of electronic storage,
it is used most often to identify fast, temporary forms
of storage. If your computer's CPU had to constantly
access the hard drive to retrieve every piece of data
it needs, it would operate very slowly. When the information
is kept in memory, the CPU can access it much more quickly.
Most forms of memory are intended to store data temporarily.
CPU accesses memory according to a distinct hierarchy.
Whether it comes from permanent storage (the hard drive)
or input (the keyboard), most data goes in random access
memory (RAM) first. The CPU then stores pieces of data
it will need to access, often in a cache, and maintains
certain special instructions in the register. We'll
talk about cache and registers later.
of the components in your computer, such as the CPU,
the hard drive and the operating system, work together
as a team, and memory is one of the most essential parts
of this team. From the moment you turn your computer
on until the time you shut it down, your CPU is constantly
using memory. Let's take a look at a typical scenario:
turn the computer on.
computer loads data from read-only memory (ROM)
and performs a power-on self-test (POST) to make
sure all the major components are functioning properly.
As part of this test, the memory controller checks
all of the memory addresses with a quick read/write
operation to ensure that there are no errors in
the memory chips. Read/write means that data is
written to a bit and then read from that bit.
computer loads the basic input/output system (BIOS)
from ROM. The BIOS provides the most basic information
about storage devices, boot sequence, security,
Plug and Play (auto device recognition) capability
and a few other items.
computer loads the operating system (OS) from the
hard drive into the system's RAM. Generally, the
critical parts of the operating system are maintained
in RAM as long as the computer is on. This allows
the CPU to have immediate access to the operating
system, which enhances the performance and functionality
of the overall system.
you open an application, it is loaded into RAM.
To conserve RAM usage, many applications load only
the essential parts of the program initially and
then load other pieces as needed.
an application is loaded, any files that are opened
for use in that application are loaded into RAM.
you save a file and close the application, the file
is written to the specified storage device, and
then it and the application are purged from RAM.
the list above, every time something is loaded or
opened, it is placed into RAM. This simply means
that it has been put in the computer's temporary
storage area so that the CPU can access that information
more easily. The CPU requests the data it needs
from RAM, processes it and writes new data back
to RAM in a continuous cycle. In most computers,
this shuffling of data between the CPU and RAM happens
millions of times every second. When an application
is closed, it and any accompanying files are usually
purged (deleted) from RAM to make room for new data.
If the changed files are not saved to a permanent
storage device before being purged, they are lost.