CompTIA A+ 2009 Exam Prep: Understanding Types of RAM

Mike Rodriguez — Wed, 18 Nov 2009 14:00:37 +0000

What is RAM?

RAM, or Random Access Memory, is a type of data storage device used by computer systems to quickly access needed information in any order that it is needed.

RAM can be used for many different things, most commonly as computer memory (primary), it can also be used in your graphics card, as cache in your CPU, in advanced sound cards, etc.

As primary memory in your computer system, RAM is used to store data so it can be accessed by your Central Processing Unit (CPU.) The more RAM you have, the less your CPU needs to reference the Hard Drive. Accessing data from your Hard Drive is a much slower process compared to the high access speeds of RAM.

RAM on the CompTIA A+ Exam

There are a few key changes concerning the types of Random Access Memory (RAM) from the 2006 CompTIA A+ exam (220-601) and the new 2009 A+ exam (220-701). The main change is the addition of Double Data Rate 3 RAM, or DDR3 RAM on the new exam.

I’ll go over each type of RAM in detail to help you get a better understanding of the differences between each one. This article will give you an in-depth view of RAM and is recommended for those who are already familiar with some technical terms, such as: clock speeds, capacitors, and transistors.

I will explain each type of memory using facts and less commentary, to help you get the most of this article and help you prepare for your CompTIA A+ certification.

Types of RAM

One of the objectives on both the 2006 and 2009 versions of the CompTIA A+ exams is to understand the different types of RAM. The types of RAM that you need to be familiar with are:

DRAM, or Dynamic RAM,
SRAM, or Static RAM,
SDRAM, or Synchronous Dynamic RAM,
DDR, or Double Data Rate (and DDR2/DDR3),
RAMBUS, or Rambus Dynamic RAM.

All of these types of RAM are types of volatile memory. Volatile memory is memory that requires constant power to store data, and once power is lost, so is the data.

Below, you will learn about each type of RAM so that you’re able to identify the name, purpose and characteristic of each for your A+ exam.

• DRAM

DRAM, or Dynamic RAM, uses capacitors to store bits of data. Those capacitors need to be refreshed often to store information. The advantage of DRAM as opposed to SRAM (Static RAM,) is that DRAM only needs 1 transistor and one capacitor per bit, as opposed to four transistors in SRAM. However, DRAM is significantly slower than SRAM.

• SRAM

SRAM, which stands for Static RAM, is similar to DRAM, except that since it uses a different type of electronic circuit (bistable latching circuitry,) it does not need to be refreshed. Although SRAM does temporarily hold data after power is lost, it is lost eventually, making it still classified as volatile memory. It is also faster and uses less power than DRAM.

• SDRAM

Synchronous Dynamic RAM, or SDRAM, is essentially DRAM that synchronizes with the system bus. By synchronizing with the system bus, it allows for more complex, albeit slower, operations. SDRAM runs as 3.3V and is described as single data rate memory. It can be found with a capacity of up to 512MB.

• DDR

Double Data Rate (DDR) RAM, is the first revision to SDRAM. It is essentially exactly the same as SDRAM, except it doubles the amount of data sent and/or received per access. DDR SDRAM runs at 2.5V, making it incompatible with SDRAM. You may also find DDR SDRAM that has been set above 2.5V, usually between 2.6 to 2.8V, to allow for faster processing.

DDR SDRAM runs at 133, 166, 200MHz, and less commonly, 275MHz. You can usually find DDR SDRAM labeled as:

“DDR 266” for the 133MHz version which fits into a PC 2100 DIMM slot,
“DDR 333” for the 166MHz version which fits into a PC2700 DIMM slot,
“DDR 400” for the 200MHz version which fits into the PC3200 DIMM slot, and
“DDR 550” for the less common 275MHz version which fits into a PC 4400 slot.

All DDR SDRAM use the 184-pin architecture. DDR memory can be found with a capacity of up to 1GB.

• DDR2

DDR2 RAM doubles the amount of data sent and/or received per access again, making it twice as fast as DDR RAM and four times as fast as SDRAM. Rather than increase the clock rate, DDR2 RAM simply makes internal operations perform in units 4 times as wide as SDRAM, making it run faster, and much cooler (temperature wise) than running at a higher rate.

Clock rates are actually cut in half, meaning rather than run at 400MHz in DDR RAM, it would run at 200MHz and achieve roughly the same speed. Since it runs at a lower clock rate, less voltage is needed to run. DDR2 memory runs standard at 1.8V, but has been set above as far as 2.2V to allow for faster processing.

DDR2 RAM speeds are as follows:

400 (PC2 3200),
533 (PC2 4200),
667 (PC2 5300 and 5400),
800 (PC2 6400),
1000 (PC2 8000),
1066 (PC2 8500) which is arguably the most common,
1100 (PC2 8800),
1150 (PC2 9200),
and 1200 (PC2 9600).

DDR2 memory can be found with a capacity of up to 4GB.

• DDR3

DDR3 RAM doubles the amount of data sent and/or received again, keeping true to the double data rate name. This means DDR3 memory is 8 times as wide as the original SDRAM. Meaning to keep up with 400MHz DDR2 memory, it only needs to run at 200MHz. DDR3 memory usually runs between 1.5V and 1.65V, which is only slightly lower than DDR2 memory, but still an improvement.

DDR3 RAM speeds are as follows:

1066 (PC3 8500),
1333 (PC3 10600, 10660, and 10666),
1600 (PC3 12800),
1800 (PC3 14400),
1866 (PC3 14900 and 15000),
2000 (PC3 16000),
2133 (PC3 17000 and 17066),
and 2200 (17600).

DDR3 memory can be found with a capacity of up to 4GB.

• RAMBUS

Rambus Dynamic RAM (RDRAM,) was developed by Rambus, Inc. for the Nintendo 64 system in 1996. It was introduced into the PC market in 1999.

RDRAM uses the same techniques as DDR systems to double the data rate of information sent and/or received. Compared to most memory standards, RDRAM shows increased latency, heat output, cost, and manufacturing complexity. However, recent improvements in the technology brought about its use in the Sony Playstation 2 (PS2) and Playstation 3 (PS3), though the PS3 version of RDRAM uses a 64-bit architecture, rather than 16 or 32-bit.

RDRAM speeds are as follows:

Single Channel 300MHz (PC 600),
Single Channel 355MHz (PC 700),
Single Channel 400MHz (PC 800),
Single Channel 533MHz (PC 1066 or RIMM 2100),
Single Channel 600MHz (PC 1200 or RIMM 2400),
Dual Channel 400MHz (RIMM 3200),
Dual Channel 533MHz (RIMM 4200),
Dual Channel 600MHz (RIMM 4800),
and Dual Channel 800MHz (RIMM 6400).

What You Need to Remember About RAM

If you’re preparing for your A+ exam, you’ll need to remember, of course, the different types of RAM: DRAM, SRAM, SDRAM, DDR, DDR2, DDR3, and RAMBUS will all be on the test. Knowing the difference between each of them is the key.

I would also recommend memorizing what the different acronyms stand for, in case they are written as such on the exam.

Also remember that volatile memory is memory that requires constant power to restore data, such as RAM, and non-volatile memory is memory that can store data even when no power supply is present, such as a Hard Drive.

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