Dual-Channel Architecture

1. Brad Traina April 7, 2009 Dual-Channel Architecture

2. Memory Hierarchy

3. Physical Memory • Physical memory, also known as RAM, stores data for use by the CPU • There are many types of physical memory, the most common used today being SDRAM

4. Random Access Memory • Random Access Memory (RAM) : stored data is to be accessed at random • Any piece of data can be returned at a constant time, regardless of its physical location • RAM is volatile, meaning all information is lost when the power is shut off

5. Who Invented RAM? • In 1966, Robert Dennard invented DRAM (dynamic random access memory) • He received a patent for his idea in 1968.

6. Computer Memory • A computer's memory (RAM) is a temporary storage area for data that needs to be accessed at high speeds. • This can help programs run more efficiently. • The processor can only work as fast as data can be passed to it from the CPU. • If the CPU is waiting on data from the memory, it is not working at its full potential. The memory needs to keep up with the CPU.

7. Single-Channel Memory • Single-Channel memory is like a funnel that feeds data to the processor through a single pipe • Data is transferred 64 bits at a time • This can create a bottleneck

8. Dual-Channel Memory • With dual-channel memory it is like having two funnels feeding data through two pipes • With two channels, data can be transferred 128 bits at a time

9. Memory Controller • The memory controller manages the data flow between the processor and the memory • Data gets sent to the memory controller which decides whether to store it in memory or send it to the processor

10. Memory Controller

11. Single-Channel Memory • Single Channel memory can be though of as a one lane street. • Data needs to flow both in and out of memory on this one lane street.

12. Dual-Channel Memory • Dual-Channel memory doubles the maximum amount of data that can be transferred between the CPU and the memory • We now have a two lane road capable of sending and receiving data at the same time.

13. Peak Bandwidth • Peak bandwidth describes the maximum amount of data processed by memory in a given time period. • It is calculated by the following formula: Memory Speed * Number of bytes transferred per channel * Number of channels

14. Performance • Notice that these transfer rates are theoretical. • They are calculated assuming that a data transfer will occur each clock cycle. • In reality, no CPU or memory controller will be transferring data 100% of the time. • For this reason 100% theoretical performance increase does not translate into a 100% performance increase of your computer.

15. Synchronous Dual-Channel • For the best dual-channel memory performance you must use identically paired memory • In order for memory to be considered Identical it must have: • The same capacity • The same speed • The same latency • This setup is referred to as synchronous dual-channel. It is the standard when you think of dual-channel memory.

16. Asynchronous dual-channel • Asynchronous dual-channel memory is quite new, and provides less performance gain when compared to synchronous dual-channel • In order to use this you must have memory: • With the same speed • With the same latency • In this case the capacity of the memory does not matter

17. Triple-Channel Memory • The new intel core i7 processor supports triple channel memory. • The memory controller is now built into the processor. • It is capable of transferring 192 bits at a time

18. End

19. Resources • http://en.wikipedia.org/wiki/Dual-channel_architecture • “Everything You Need to Know About Dual Channel • By Gabriel Torres • http://www.hardwaresecrets.com/article/133/1 • http://www.devhardware.com/c/a/Memory/Dual-Channel/ • “Intel Dual-Channel DDR Memory Architecture White Paper” • By Infineon Technologies and Kingston Technology • http://www.kingston.com/newtech/MKF_520DDRWhitepaper.pdf