Upgrading & Fixing Laptops DUMmIES

Staying current with modern memory ..............................................

The good news is that memory makers keep coming up with ways to boost the

speed and capacity of RAM. And even better, they have generally managed to

keep the relative prices of memory on a steep downward spiral: you almost

certainly pay the same or less today for a memory module that is significantly

larger than last year’s (or last month’s) latest and greatest. The not-quite-so-

good news is that there is a dizzying array of available memory types, and

you’ve got to match your module to the laptop you are upgrading. Start with

the memory type and then find it in the proper physical module size.

Here’s a quick tour of the most modern RAM designs used in laptops.

DDR

Double Data Rate (DDR)is an advanced form of SDRAM (about which you

read more in a moment). The most common means of identifying DDR is like

this: PC1600, PC2100, PC2700, and PC3200.

In that usage, the numbers refer to the total bandwidth of the entire module,

whether there is one, two, four, or however many memory chips soldered to

the little SODIMM. The higher the number, the greater the bandwidth and there-

fore the faster the memory can work with your system.

Less commonly, DDR can also be rated in this way: DDR333, DDR400, and so

on. In this usage, the designer identifies the data transfer rate of the compo-

nents. PC1600 was originally designed for systems with a 100 MHz front-side

bus. Since these modules are DDR — Double Data Rate, you recall — that

means they are capable of 200 mega-transfers per second (MT/s). You’re deal-

ing with computer words of eight bits, so you’ve got 200 MT/s times eight, or

1,600. A PC1600 module has a total bandwidth of 1.6GB of data per second,

which is where the 1600 number comes from.

88 Part II: Explaining What Could Possibly Go Wrong

when computer designers talk about a 16K chip

they mean a circuit capable of dealing with

16 ×1,204 bits of information, or 16,384 bits.

In large numbers like those on a hard disk drive,

the math starts to get fuzzy. Consider the giga-

byte: In technical terms a gigabyteis 1,024

megabytes or 1,024×1,024×1,024. A designer may

come up with a 40GB hard drive, and that’s what

it is called in the lab because it contains 40 giga-

bytes. But if you convert the binary to decimal,

the capacity totes up to 43,980,465,111,040 bytes.

When the marketing department gets hold of

that new drive, they start printing up labels that

say: “44GB.”

(continued)