Transcript presentation source

3/24 How RAM Works.
• Roll Call
• Video Bits (2)
• Lecture:
–
–
–
–
transistors
capacitors
writing to RAM
reading from
RAM
How a Transistor works.
• Two electrical
pathways:
Data OUT
Addresser
Data IN
– addresser
– data
Silicon dioxide
N-type silicon
polysilicon
P-type silicon
How a Transistor works.
• The addresser
sends a small
+
Data IN
Data OUT
positive electrical
+
charge.
• This charge makes
the polysilicon
N-type silicon
polysilicon
positively charged.
P-type silicon
• The silicon dioxide
(SiO2) is inert. It is
unaffected.
Addresser
How a Transistor works.
• The positively
charged polysilicon
Data OUT
attracts negative
charges in the Ptype silicon.
Addresser
Data IN
+
+
--- -- -- --
N-type silicon
polysilicon
P-type silicon
How a Transistor works.
• The negative
charge in the P+
Data IN
Data OUT
type
silicon
--+
provides a bridge
- --- ----- -- -- - - for the “Data”
charge to go from
N-type silicon
polysilicon the N-type silicon
by the Data IN to
P-type silicon
the N-type by the
Data OUT.
Addresser
Capacitors.
Address Line
Capacitor
Data Line
• A capacitor can
store an electric
charge briefly.
• Capacitors in the
RAM are
replenished
thousands of times
per second.
RAM.
• Thousands of these
transistor and
capacitor sets are
on a single chip in
the RAM modules.
• They are organized
with address lines
and data lines.
Address Lines & Data Lines.
• Address lines
locate a spot in the
chip where data
can be stored.
• Data lines send (or
accept) the signal
to (or from) the
location specified.
Writing Data to RAM.
• The address lines
point out the spot.
• The data lines send
electrical pulses to
charge the
capacitors.
Reading Data from RAM.
• The address lines
point out the spot.
• The data lines
sense the electrical
charge put off by
the capacitor.
Types of RAM.
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DRAM
EDO RAM
VRAM
SRAM
SIMMs
DIMMs