Types
of RAM
1.
Dynamic Random Access Memory (DRAM)
•Contents
are constantly refreshed 1000 times per second
•Access
time 60 – 70 nanoseconds
Note: a nanosecond
is one billionth
of a second
2.
Synchronous Dynamic Random Access Memory (SDRAM)
•Quicker
than DRAM
•Access
time less than 60 nanoseconds
3.
Direct Rambus
Dynamic Random Access Memory (DRDRAM)
•New
type of RAM architecture
•Access
time 20 times faster than DRAM
•More
expensive
:+mn- �oo�[�
mso-color-index:1;mso-font-kerning:12.0pt;language:en-GB'>is one billionth
of a second!4. Static Random Access Memory (SRAM)
•Doesn’t
need refreshing
•Retains
contents as long as power applied to the chip
•Access
time around 10 nanoseconds
•Used
for cache
memory
•Also
for date
and time settings as powered
by small battery
5.
Cache memory
•Small
amount of memory typically 256 or 512 kilobytes
•Temporary
store for often used instructions
•Level 1
cache is built within the CPU (internal)
•Level 2
cache may be on chip or nearby (external)
•Faster
for CPU to access than main memory
•Also
for date
and time settings as powered
by small battery
6.
Video Random Access memory
•Holds
data to be displayed on computer screen
•Has
two data paths allowing READ and WRITE to occur at the same time
•A
system’s amount of VRAM relates to the number of colours and resolution
•A
graphics card may have its own VRAM chip on board
lD�lc�[�or-index:1;mso-font-kerning:12.0pt;language:en-GB;
font-weight:bold'>Level 2
cache may be on chip or nearby (external)
•Faster
for CPU to access than main memory
7.
Virtual memory
•Uses
backing storage e.g. hard disk as a temporary location for programs and
data where insufficient RAM available
•Swaps
programs and data between the hard-disk and RAM as the CPU requires them for
processing
•A
cheap method of running large or many programs on a computer system
•Cost
is speed: the CPU can access RAM in nanoseconds but hard-disk in milliseconds
(Note: a millisecond is a thousandth of a second)
•Virtual
memory is much slower than RAM
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