1. 3/24 How RAM Works. Roll Call Video Bits (2) Lecture: –transistors –capacitors –writing to RAM –reading from RAM

2. How a Transistor works. Two electrical pathways: –addresser –data Addresser Data INData OUT polysiliconN-type silicon P-type silicon Silicon dioxide

3. How a Transistor works. The addresser sends a small positive electrical charge. This charge makes the polysilicon positively charged. The silicon dioxide (SiO 2 ) is inert. It is unaffected. polysiliconN-type silicon P-type silicon + + Addresser Data INData OUT

4. How a Transistor works. The positively charged polysilicon attracts negative charges in the P- type silicon. polysiliconN-type silicon P-type silicon + + -- - - - - - - - Addresser Data INData OUT

5. How a Transistor works. The negative charge in the P- type silicon provides a bridge for the “Data” charge to go from the N-type silicon by the Data IN to the N-type by the Data OUT. polysiliconN-type silicon P-type silicon + + --- --- -- - -- - - - - - - - - - Addresser Data INData OUT

6. Capacitors. A capacitor can store an electric charge briefly. Capacitors in the RAM are replenished thousands of times per second. Capacitor

7. 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.

8. 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.

9. Writing Data to RAM. The address lines point out the spot. The data lines send electrical pulses to charge the capacitors.

10. Reading Data from RAM. The address lines point out the spot. The data lines sense the electrical charge put off by the capacitor.

11. Types of RAM. DRAM EDO RAM VRAM SRAM SIMMs DIMMs