FREE Tutorial
MEMORY TYPES
DESCRIPTION
This tutorial is taken from our A+ Certification PC Hardware Support Module 5 - Motherbaords and Components training course. It explains the differences in memory types usually found within a PC.
|
|
TUTORIAL TAKEN FROM COURSE :
A+ SYLLABUS 10 - MODULE 5 - MOTHERBOARDS AND COMPONENTS
FULL COURSE DETAILS
At the end of this course you will be able to: define the following processor terminology: clock speed, processor cache, data bus, address bus, register, multi-tasking, multi-processing, real mode, protected mode, virtual real mode; define the addressable memory capacity, processing speeds, register size and data bus size of the Intel 486 and Pentium range of processors; describe processor sockets, their characteristics and processor compatibility; describe the following memory types: DRAM, SRAM, WRAM, and give examples of how they are used; describe the characteristics of different types of memory packaging, such as DIPP, SIMM and DIMM; name two different types of memory error detection; describe the standard components of a motherboard including: chipset, clock, I/O ports, memory slots, Level 2 cache; describe the features of AT, ATX, LPX and NLX systems board form factors; describe the features of ISA, MCA, EISA, VESA, PCI and PCMCIA buses. This set of modules will prepare the reader for the exam 220-301.
TO ACCESS THE FULL COURSE AND HUNDREDS OF OTHERS, CLICK HERE.
|
|
Memory Types
RAM and ROM
RAM and ROM are the two basic types of chip-based storage in the PC. RAM and ROM memory are used to store data to which fast access is required. Due to its high cost, RAM and ROM memory is not used to store large amounts of data permanently, such as databases and word-processing documents.
- RAM is most commonly used as the temporary "working space" of the CPU and other components of the PC, such as video cards. RAM is volatile, meaning that the information it holds is dependent on a constant supply of power. All data stored in it will be lost if the computer is rebooted or turned off.
- ROM is typically used to store low-level hardware instructions such as the motherboard and video-card BIOS. ROM is non-volatile and does not require a permanent power source to retain data.
Random Access Memory (RAM) Types
RAM is the workspace of the processor. The CPU uses this storage space to hold both program instructions and associated data.
Dynamic Random Access Memory (DRAM)
DRAM is used as the main or system memory of a PC. It stores the operating system, application programs and data while they are running.
DRAM stores data bits as electrical charges within the structure of a single transistor. Each bit cell is very small but the electrical charge gradually discharges, causing the memory cell to lose its information. In order to preserve the information, dynamic memory has to be refreshed periodically by accessing each bit cell at regular intervals. The refresh cycles slow down the operation of DRAM but it is popular, mainly because of its high-density (MB per chip) and low price.
Standard DRAM does not have any special compatibility issues. A modern system is unlikely to use standard DRAM, but will use one of the following types of DRAM:
Fast Page Mode DRAM
Fast Page Mode (FPM) DRAM offers faster accesses than standard DRAM. While standard DRAM requires that a row and column address be sent for each access to a memory cell, FPM sends the row address just once for many accesses to memory in locations near each other. This improves access time.
Extended Data Output DRAM
Extended Data Output (EDO) DRAM uses a modified chip design that provides improvements in read times of up to 30%. This performance gain is achieved by continuing to output data from one address, while simultaneously setting up the access request for the next one.
Burst Extended Data Output DRAM
Burst Extended Data Output (BEDO) DRAM is supported by some motherboards, but has not gained wide acceptance. It is similar in performance to Synchronous DRAM.
Synchronous DRAM
Synchronous DRAM (SDRAM) is designed to run at the motherboard clock speed. SDRAM can run at much higher clock speeds than other types of DRAM and will be able to cope with faster motherboard designs as they appear on the market.
SDRAM is available in three clock speeds: 66, 100, and 133MHz.. Motherboards are designed to support specific types of RAM. You should always check which types of memory can be fitted before supplying or installing upgrades.
RDRAM (Rambus)
Rambus DRAM (RDRAM) has an effective clock speed of up to 800MHz, compared to SDRAM's 133MHz. However, RDRAM has a bus width of 2 bytes as opposed to SDRAM's bus width of 8 bytes. The result is that RDRAM can achieve speeds of up to 1.6 GB/sec, while SDRAM can achieve speeds of up to 1.064 GB/sec.
RDRAM is a proprietary memory type and manufacturers who want to use it in their products must pay a license fee to Intel and Rambus.
DDR SDRAM
Double Data Rate SDRAM (DDR SDRAM) is a variant of SDRAM where data is transferred twice in one cycle. It is available at speeds from 100Mhz to 166Mhz. The theoretical maximum bandwidth for 100Mhz DDR is 1.6 GB/sec (100Mhz x 2 x 8 bytes). DDR is not as expensive as Rambus.
SDRAM is referred to by the clock speed (PC100, PC133, and so on). DDR and the latest Rambus chips are labeled using the maximum theoretical bandwidth (PC1600, PC2100, and so on) - largely for marketing reasons.
Static Random Access Memory (SRAM)
Static RAM stores data in an electronic circuit called a flip-flop. SRAM is approximately four or five times faster than DRAM. Since every bit cell requires six or more transistors to function under SRAM, compared to one per bit for DRAM, SRAM modules are relatively larger and more expensive than DRAM. They are normally reserved for speed critical functions, such as the system cache.
VRAM
VRAM (or dual-port RAM) is used on high-performance video adapters. Unlike conventional RAM, VRAM has two data ports: one for read operations and one for write operations. This makes it possible for the system to write data to memory at the same time as data is being read, greatly improving video system performance.
VRAM video RAM should not be confused with video RAM. Video RAM is often incorrectly abbreviated to VRAM.
WRAM
Window RAM (WRAM) is a modification of VRAM that improves performance and reduces cost. Designed specifically for use in graphics cards, WRAM is also dual-port RAM, but is about 25% faster than VRAM. WRAM was first made popular by Matrox's Millennium series of graphics cards.
SGRAM
Synchronous Graphics RAM (SGRAM) tackles the poor performance of regular DRAM by greatly increasing the speed at which memory transfers take place. SGRAM is designed to work with acceleration features built into video cards to greatly improve overall video processing speed. SGRAM is single-port RAM, unlike VRAM or WRAM, but, due to its advanced design, SGRAM offers performance that is much closer to VRAM than DRAM.
|
|
|
|
