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Memory types- introduction

The capabilities of a server depend on the type and capacity of its

memory. Memory is the internal storage area that stores data and

program instructions. There are various types of memory available

today.

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Introduction to DRAM

The physical memory installed on a server is called RAM. The mostcommon form of RAM is the Dynamic RAM (DRAM). In this type ofmemory data is stored in the form of electrical charges in capacitorsand transistors. Therefore, this type of memory needs to becontinuously refreshed.

DRAM is not recommended for long-term storage

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Types of DRAM

Asynchronous DRAM

SDRAM

RDRAM

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Server Memory Requirements

The type of the memory considered for a server depends on its

functionality and the number of clients. Because servers perform

many operations at a time, a server with large of clients Prefers

DDR and DDR2.

RDRAM is not used on many servers because it is expensive.

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Memory Specification

Different types of memory have different technical specifications.

These specifications determine how processors access memory,

correct errors in data and cache repeatedly used data.

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Technical Specifications of Memory

Memory Interleaving

Error Correction

Memory Buffering

Registered Memory

Caching

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Memory Interleaving

Memory Interleaving is an advanced technique in which is an advanced

technique in which the processor simultaneously accesses more than one

memory bank, rather than accessing sequentially.

This helps increase the memory bandwidth and, in turn, improves memory

performance on multibanked motherboards and chipsets.

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Error Correction

The most basic form of an error detection technique is parity checking. The

Error-Correcting Code (ECC) memory uses these parity checking

operations to test the accuracy of data as data passes in and out of

memory.

On each ECC memory, there are one or two additional chips to store the

parity check bits. As a result, ECC memory is more expensive than

regular memory.

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Extended ECC

Extended ECC is an enhanced version of the ECC. This checking

and correction code protects not only the memory, but also major

system buses such as the PCI bus and IDE buses.

Extended ECC protects the data from intermittent signal faults.

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Memory Buffering

Buffered memory refers to the memory that consists of additionalchips between the memory and chipset. These chips help inbuffering data when the chipset and memory communicate.

In addition, a large amount of memory requires sizable electricalload. The buffer in the memory electrically isolates it and helps thechipset manage the load.

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Registered Memory

Registered memory refers to memory modules comprising resisters.These registers buffer data before it reaches the motherboard.

Also as registered memory makes high-speed access more reliable,high-end motherboards use registered memory. However registeredmemory costs more than non-registered memory.

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caching

Most programs use the same data and instructions repeatedly. Amemory cache is a high speed static RAM (SRAM) that stores thisrepeatedly used data. The CPU can avoid accessing the slow mainmemory by using the data it needs from this high speed memorycache.

This further leads to enhanced processing speed.

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Caching-types

Level 1

Level 2

Level 3

These caches comprise extremely high-speed memory and provide

a place to store instructions and data that may be used again by the

CPU.

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HCL (Hardware Compatibility List)

Manufacturers test certain types of hardware for compatibility withdifferent operating systems. The components that Pass thecompatibility tests are listed in a Hardware Compatibility List.

HCL comprises lists of all computers and peripherals that have beentested for compatibility with the particular operating system.