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CompTIA® A+™ Core 1 Exam Notes :Compare And Contrast Ram Types And Features

1.3 Compare and contrast RAM types and features

1. There are basically two important types of RAM (Short for Random Access Memory):

  1. a. SRAM - Static RAM being expensive, primarily used for Cache memory. DRAM, being cheaper, is used for main memory. SRAM is widely used for Level 1, Level 2 or Level 3 cache memory. Level 1 cache is internal to the processor, and level 2 and level 3 caches are external to the processor, it resides on the motherboard.

  2. b. DRAM: Dynamic RAM holds its data if it is continuously accessed by special logic called a refresh circuit. If the memory is not refreshed regularly, then the DRAM will lose its contents. This refreshing action is why the memory is called dynamic. All PCs use DRAM for their main system memory, instead of SRAM, even though DRAMs are slower than SRAMs and require the overhead of the refresh circuitry. The reason that DRAMs are used is that they are much cheaper and take up much less space.

2. RAM is much faster than ROM is, due to the nature of how it stores information. For this reason, RAM is often used to shadow the BIOS ROM to improve performance when executing BIOS code. PROM (Programmable ROM) is also a version of ROM and is slower compared to RAM.

3. The computer main memory usually consists of some type of DRAM. Types of DRAM Packages and DRAM Memory are explained below:

  1. a. 168 pin DIMM (SDRAM): It can run at much higher clock speeds than conventional memory. SDRAM actually synchronizes itself with the CPU's bus and is capable of running at 133 MHz and twice as fast EDO DRAM .

  2. b. 184 pin DIMM (DDR-SDRAM): It supports data transfers on both edges of each clock cycle, effectively doubling the memory chip's data throughput. DDR-SDRAM is also called SDRAM II. DDR stands for Double Data Rate.

  3. c. 240 DIMM (DDR2-SDRAM): It supports higher speeds than it's predecessor DDR SDRAM.DDR2 SDRAM is a double data rate synchronous dynamic random-access memory interface. It supersedes the original DDR SDRAM specification and has itself been superseded by DDR3 SDRAM. DDR2 is neither forward nor backward compatible with either DDR or DDR3.

  4. d. 240 DIMM (DDR3-SDRAM): It supports speeds faster than DDR2 SDRAM. DDR3 SDRAM, an abbreviation for double data rate type three synchronous dynamic random access memory, is a modern kind of dynamic random access memory (DRAM) with a high bandwidth interface, and has been in use since 2007. DDR3 SDRAM is neither forward nor backward compatible with any earlier type of random access memory (RAM) due to different signaling voltages, timings, and other factors

4. PC ratings and corresponding DDR bandwidth are given below:

  1. DDR266 = PC2100

  2. DDR333 = PC2700

  3. DDR400 = PC3200

  4. DDR2-400 = PC2-3200

  5. DDR2-533 = PC2-4200

  6. DDR2-667 = PC2-5300

  7. DDR2-800 = PC2-6400

  8. DDR3-800 = PC3-6400

  9. DDR3-1066 = PC3-8500

  10. DDR3-1333 = PC3-10600

  11. DDR3-1600 = PC3-12800

  12. DR400 memory is also referred to as PC3200 memory. 400MHz DDR2 memory would be listed as PC2-3200, and so on.

5. The first 3 octets of a MAC address provide the manufacturer of the NIC (Network Interface Card). For example, consider the MAC address given below:

  1. 00-22-75-76-D7-91

  2. 00-22-75 will uniquely identify the manufacturer of the NIC, which in this case turns out to be Belkin International Inc.

  3. However, please note that identifying the manufacturer is only half a job, and you may need to try different drivers from that manufacturer to troubleshoot the problem

6. Dual-channel-enabled memory controllers in a PC system architecture utilize two 64-bit data channels. Dual channel should not be confused with double data rate (DDR), in which data exchange happens twice per DRAM clock. The two technologies are independent of each other and many motherboards use both, by using DDR memory in a dual-channel configuration. Dual-channel architecture requires a dual-channel-capable motherboard and two or more DDR, DDR2 SDRAM, or DDR3 SDRAM memory modules.

7. Error-correcting code memory (ECC memory)

  1. a. ECC is a type of computer data storage that can detect and correct the more common kinds of internal data corruption.

  2. b. ECC memory is used in most computers where data corruption cannot be tolerated under any circumsta nces, such as for scientific or financial computing. Error-Correcting Code (ECC) memory is often seen in high-end motherboards that provide important services or software functions. Unlike normal parity memory, ECC memory can find and fix errors.

  3. c. ECC memory generally costs more, so you usually see motherboards designed for ECC memory when there's a specific need. ECC memory maintains a memory system effectively free from single-bit errors: the data that is read from each word is always the same as the data that had been written to it, even if a single bit actually stored, or more in some cases, has been flipped to the wrong state.

  4. d. ECC memory is used where the data needs to be very accurate, and the memory is required to have self correcting capability. It adds cost to the memory module and used in server level computers where data accuracy is very important. Some non-ECC memory with parity support allows errors to be detected, but not corrected; otherwise errors that may occur are not detected.

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