Hardware Reference
In-Depth Information
Figure 1.17
Motherboard layout for a modern PC supporting multiple bus
standards
Most memory device consist of a matrix of cells arranged on the basis of
rows and columns. A
row address strobe
(RAS) signal is used to latch the row
address of a particular memory location whilst a
column address strobe
(CAS)
signal is used to latch the column address of a particular memory location into
the row-column matrix of a RAM device.
CAS latency
is the ratio of column
access time to clock cycle time.
In addition, modern large-scale memories are based on dynamic RAM
(DRAM) technology in which the data is stored as a tiny electric charge which
will leak away if it is not periodically
refreshed
. The process of reading and
then writing back the data stored in a DRAM device is known as
refreshing
,
and this process must operate continuously otherwise data will be lost.
Memory organization
The memory in a PC is usually arranged in
banks
. Many modern PCs have
two or more memory banks (i.e. Bank A, Bank B, and so on) and each bank
comprises a group of adjacent sockets or modules. The banks are usually easily
