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Memory

Memory. What is memory and Why it is required. A computer uses memory to hold temporary instructions and data needed to complete tasks. This enables the computer ’ s Central Processing Unit, to access instructions and data stored in memory very quickly. Difference between Memory and storage.

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Memory

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  1. Memory 22 Jun 2006

  2. What is memory and Why it is required • A computer uses memory to hold temporary instructions and data needed to complete tasks. • This enables the computer’s Central Processing Unit, to access instructions and data stored in memory very quickly. 22 Jun 2006

  3. Difference between Memory and storage • The term memory refers to the amount of RAM installed in the computer, whereas the term storage refers to the available amount of hard disk capacity. • Another important difference between memory and storage is that the information stored on a hard disk remains intact even when the computer is turned off. However, any data held in memory is cleared when the computer is turned off. • The computer memory holds any changes you make to a document until you save the changes to a disk. If anything interrupts the computer’s operation— such as a power outage or system error— any changes made, but not saved, are lost. 22 Jun 2006

  4. Types of Memory • DDR • DDR-2 Further it is classified into • Registered • Unbuffered • FBD 22 Jun 2006

  5. What is DDR memory • DDR stands for Double Data Rate • DDR reads data on both the rising and falling edges of the clock signal. • The double data rate architecture is essentially a 2n prefetch architecture, with an interface designed to transfer two data words per clock cycle at the I/O pins. 22 Jun 2006

  6. DDR Memory Number of Pin=184 Voltage Requirement=2.5V 22 Jun 2006

  7. DDR-2 Memory • Number of Pins=240 • Voltage=1.8V • The I/O buffers are clocked at twice the core frequency. In order to satisfy the output, DDR I prefaces 2 bits, DDR II needs to prefects four bits with every read command and pipeline them for time multiplexed output. 22 Jun 2006

  8. Registered Memory • On Registered DIMM's the address and control signals from your motherboards chipset get intercepted and buffered by two or three register chips on the module . • Store and forward method is implemented. • Because the address and control signals only have to go to the register chips on a Registered DIMM, instead of each and every RAM chip on all the memory modules installed in your computer, the load on your motherboard chipset's address and control pins is greatly decreased. • This decrease in load allows the motherboard's chipset to drive the address and control signals quickly enough to remain stable when a large amount of memory is installed. 22 Jun 2006

  9. Registered Memory 22 Jun 2006

  10. Unbuffered Memory • Memory controller drives the memory directly. • Suitable for Gaming application 22 Jun 2006

  11. Single Channel and Dual Channel Memory 22 Jun 2006

  12. To illustrate the difference between single- and dual-channel In this illustration, single-channel memory is like a funnel that feeds data to the processor engine through a single pipe. Data is transferred 64 bits at a time. Peak Bandwidth is calculated as: Memory Speed x Number of bytes transferred per channel x Number of Channels (its data rate) (8 Bytes or 64 bits) (one or two) For PC3200, also known as DDR400, modules on a dual-channel motherboard, Peak Bandwidth = (400 MHz) x (8 Bytes) x (2 Channels) = 6400 Megabytes per second (MB/s) or 6.4 Gigabytes per second (GB/s) 22 Jun 2006

  13. How to calculate how much memory is in a module • A module consists of a group of chips. If you add together the capacities of all the chips on the module, you get the total capacity of the module. 22 Jun 2006

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  15. It's easy to calculate the capacity of a memory module if you know the capacities of the chips on it. • If there are eight 64Mbit chips, it's a 512Mbit module. • The capacity of a module is described in megabytes, not megabits, you have to convert bits to bytes. 22 Jun 2006

  16. What are the components present in a memory module • PCB • DRAM • SPD - When a computer system boots up, it must “detect” the configuration of the memory modules in order to run properly. Parallel Presence Detect is the traditional method of relaying the required information by using a number of resistors. PPD is the method SIMMs and some DIMMs use to identify themselves. Serial Presence Detect uses an EEPROM (Electrically Erasable Programmable Read-Only Memory) to store information about the module. 22 Jun 2006

  17. DDR/DDR-2 Comparison 22 Jun 2006

  18. Error Correction Code Technique • It is a more comprehensive method of data-integrity checking that can detect and correct single-bit errors. Due to price competition, it is becoming more common among personal computer manufacturers not to use data integrity checking. They are eliminating the need for more expensive parity memory, for example, to lower the price of their computers. (This trend is complemented by the increased quality of memory components available from certain manufacturers and, as a result, the relative infrequency of memory errors.) 22 Jun 2006

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