Information Technology Reference
In-Depth Information
Electrically Erasable Programmable ROM
(EEPROM)
ROM that can be erased and repro-
grammed with electricity.
◾
ROM-BIOS: A motherboard has an
EEPROM
chip that contains
the low-level startup instructions for the hardware. To prevent cor-
ruption that would prevent the system from starting up, this chip is
not rewritable except with a special utility program.
◾
Caches:
The caches in a CPU are a type of static RAM (SRAM).
◾
USB flash drives, memory cards, and solid-state hard drives:
These devices use a type of EEPROM to store data. This type of
EEPROM is also called flash memory; its enhanced technology allows
data to be written and rewritten to it multiple times.
Understanding System Memory
Each computer has a certain amount of
system memory
, also called
RAM or main memory. It is dynamic RAM (DRAM), so it loses its con-
tents if it is not constantly being electrically refreshed.
system memory
The main pool of dynamic
RAM (DRAM) on the motherboard.
System memory forms a workspace that the operating system uses. When
you open an application, that application is placed in system memory,
and when you open a data file, it is placed there too. When you make
changes to a data file, those changes wait in memory until you write
them to a more permanent storage area by saving your work. The more
system memory you have, the more applications and files you can have
open at once.
paging file
The area of the hard drive set aside
for use as virtual memory. Also called a
swap file
.
virtual memory
Memory that is simulated
by swapping data out of memory and storing it
temporarily on the hard drive.
Windows also uses
virtual memory
to help prevent a computer from running out of memory. Virtual memory
is a file on the hard drive used as an extension to main memory. This file is called the
paging file
or
swap
file.
When the physical memory gets full (or nearly full), Windows moves some data to the paging file on the
hard drive. When a program requests that data, Windows moves something else out of memory, swaps the
old data back in again, and then responds to the request.
NOTE
dual inline memory module (DIMM)
A
small rectangular circuit board that holds DRAM,
fitting into a memory slot on a motherboard.
Physically, system memory comes mounted on small rectangular circuit
boards called
dual inline memory module (DIMM)
. These circuit
boards fit into memory slots on the motherboard. There are differ-
ent types and speeds of DIMMs, so you must match the memory
to the motherboard's requirements. Figure 2.3 shows two different
types of DIMMs. For notebook computers,
small outline DIMMs
(SO-DIMMs)
are used instead; they do the same thing as DIMMs but
are a different size and shape.
synchronous dynamic RAM (SDRAM)
DRAM that operates at the speed of the
system clock.
single data rate SDRAM (SDR SDRAM)
SDRAM that performs one action per clock tick.
double.data rate SDRAM (DDR SDRAM)
SDRAM that performs two actions per clock tick.
© iStockphoto.com/aguirre_mar, © iStockphoto.com/mkos83
Figure.2 3
Some DIMMs have a metal plate covering the chips for better heat dissipation.
