pace it - introduction to ram

Random access memory (RAM).

Instructor, PACE-IT Program – Edmonds Community College

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PC Hardware

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Qualifications Summary

Education

M.B.A., IT Management, Western Governor’s University

B.S., IT Security, Western Governor’s University

Entrepreneur, executive leader, and proven manger

with 10+ years of experience turning complex issues

into efficient and effective solutions.

Strengths include developing and mentoring diverse

workforces, improving processes, analyzing

business needs and creating the solutions

required— with a focus on technology.

PACE-IT.

– Introducing RAM.

– Types of dynamic RAM.

– Special consideration of RAM.

Random access memory.

When most people talk about computer memory, they are talking about dynamic random access memory (DRAM).

DRAM is not the only type of memory that is

present, but it is the one that most people are

familiar with. DRAM is used to hold data and pass it

between the CPU and storage devices. We use

DRAM because it is quicker and more responsive

than using the storage device itself, and it can hold a

lot more data than the CPU.


– How it works.» Uses transistors and capacitors to hold electrical

charges.

» Uses arrays of transistors (registers) to hold binary data.

» The registers are either on or off (binary 1 or 0).

» No electricity, no memory.

– Static RAM (SRAM).» Located on the CPU die, or just off of it (commonly called

cache or cache memory).

» Super fast.

» Expensive.

– Dynamic RAM.» Always located off the die.

» Fast, but not as fast as SRAM.

» Relatively inexpensive.


The dual inline memory module (DIMM) is both obsolete and cutting edge.

Before the introduction of the DIMM, memory

modules could only receive current through one side

of their electrical contacts. This limited the memory

bus to only being 32 bits wide. The DIMM could

receive electrical current through both sides of the

contact and the memory bus grew to 64 bits wide.

All current RAM are a type of DIMM.


– Synchronous dynamic RAM (SDRAM).» True beginning of modern RAM (industry standard

beginning in 1993).

» Synchronized with the system clock and could perform

an operation with every cycle of the clock.

» Currently considered obsolete.

– Double data rate (DDR) RAM.» Introduced in 1996.

» Effectively doubled the possible rate of data transfer by

taking advantage of the rising and falling edges of the

clock cycle (two operations per cycle).

» Speed of the RAM is determined by a specific formula:

clock rate X 2 X 64 /8 = MB transfer rate.


– Rambus DRAM (RDRAM).» A proprietary standard developed by Rambus, Inc. that

was initially supported by Intel.

» Had to either be installed in pairs, or it had to use a

special device called a continuity module (also called a

RIMM) in order to function.

» Not as cost effective as DDR.

– DDR2 and DDR3.» DDR2 doubled DDR’s performance = clock rate X 4 X 64

/8.

» DDR3 doubled DDR2’s performance = clock rate X 8 X

64 /8.

– Small outline dual inline memory

module (SODIMM).» Compact memory modules that are used in small form

factor computers (laptops in most cases).

» They can be DDR, DDR2, DDR3, etc.


– Parity vs. non-parity RAM.» Parity RAM modules have an extra bit (a parity bit) that is

used to check for errors in RAM. They can’t fix the error.

» More expensive than non-parity RAM and not really

needed anymore.

– Error-correcting code (ECC) vs.

non-ECC RAM.» ECC RAM can detect and recover from (correct) errors in

memory.

» Much more expensive, but should be used in situations

where an error can’t be tolerated.

– Dual sided vs. single sided RAM.» Dual sided RAM is when the memory modules on a stick

are separated in ranks; only one rank may be accessed

at a time.

» Single sided RAM is when the memory modules are not

separated into ranks; it is faster but more expensive than

dual sided RAM.


– Single channel vs. multi-channel RAM.» Single channel: all banks (slots) of RAM share a single

64 bit bus to the CPU.

» Multi-channel RAM: the banks of RAM may be grouped

together to form a wider bus to the CPU (128 bit or 192

bit).

» To take advantage of the multi-channel capabilities, the

RAM must be installed in matched sets.

» Follow the motherboard documentation when installing

multi-channel RAM.

– Know what type of RAM your MB

supports.» A motherboard will only support one type of RAM (DDR,

DDR2, DDRs); you can’t mix them together.

» The RAM modules are keyed on the bottom so that they

can’t be placed in the wrong type of RAM slots.

» You can install different speeds of RAM together, but the

RAM will only function at the speed of the slowest

module.



Computer memory usually refers to dynamic random access memory.

SRAM is quicker but much more expensive.

Topic

Introducing RAM.

Summary

The DIMM is both ancient and new. All modern RAM is a type of DIMM.

Modern RAM started with SDRAM and is currently working through DDR3.

Parity RAM uses an extra bit to check for errors, but can’t recover from

(correct) those errors. ECC RAM can recover from (correct) memory errors

but is very expensive. Double sided RAM uses ranks; single sided doesn’t.

Types of RAM.

RAM may be used in single or multi-channel configurations, depending on

the motherboard. When used in a multi-channel situation, follow the

motherboard’s installation instructions. RAM may not be mixed and

matched between types, but it can be done by speed. When RAM speeds

don’t match, all RAM functions at the speed of the slowest.

Special considerations of

RAM.

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