CompTIA A+ Certification All-in-One Exam Guide, Exams 220-1001 & 220-1002

by Mike Meyers

B. Disconnected CPU fan

There’s nothing wrong. It usually takes a couple of days for RAM to acclimate to the new system.

A. He forgot to disconnect the CPU fan.

B. He forgot to apply thermal paste between the CPU and the heat-sink and fan assembly.

1001

DDR SDRAM for desktops comes in 184-pin DIMMs.

DDR SDRAM for laptops comes in either 200-pin SO-DIMMs or 172-pin micro-DIMMs (see

pin DDR SDRAM micro-DIMM (photo courtesy of Kingston/Joint Harvest)

DDR, DDR RAM, and the weird hybrid, DDRAM.

To determine the bytes per second, take the MHz speed and multiply by 8 bytes (the width of all DDR SDRAM sticks). So 400 MHz multiplied by 8 is 3200 megabytes per second (MBps). Put the abbreviation “PC” in the front to make the new term: PC3200.

DDR Speeds

DDR4. Make sure you know their individual characteristics and differences. DDR3 DIMMs have 240 pins, for example, and DDR3 SO-DIMMs have 204 pins. DDR3 doubles the buffer of DDR2 from 4 bits to 8 bits, giving it a huge boost in bandwidth over older RAM. Not only that, but some DDR3 (and later) modules also include a feature called XMP, or Extreme Memory Profile, that enables power users to overclock their RAM easily, boosting their already fast memory. DDR3 modules also use higher-density memory chips, up to 16-GB DDR3 modules. AMD’s version of XMP is called AMP, for AMD Memory Profile. NOTE Do not confuse DDRx with GDDRx; the latter is a type of memory used solely in video cards (e.g., GDDR5). See Chapter 17, “Display Technologies,” for the scoop on video-specific types of memory. Some motherboards that support DDR3 also support features called triple-channel architecture or quad-channel architecture, which work a lot like dual-channel, but with three or four sticks of RAM instead of two. More recently, Intel and AMD systems have switched back to dual-channel, although there’s plenty of systems out there using triple- or quad-channel memory. EXAM TIP Be sure you are familiar with single-, dual-, triple-, and quad-channel memory architectures.

Virtual Memory Computers use a portion of the hard drive (or solid-state drive) as an extension of system RAM called virtual

from memory Figure 4-24 Program B stored in the page file, making room for Program D

Mass Storage Technologies

Historical/Conceptual

Magnetic Hard Drives

traditional hard disk drive (HDD) is composed of individual disks, or platters, with read/write heads on actuator arms controlled by a servo motor—

The aluminum platters are coated with a magnetic medium. Two tiny read/write heads service each platter, one to read the top of the platter and the other to read the bottom of the platter (see Figure 8-2). Each head has a bit-sized transducer to read or write to each spot on the drive. Many folks refer to traditional HDDs as magnetic hard drives, rotational drives, or sometimes platter-based hard drives.

1001

Hard drives run at a set spindle speed, with the spinning platters measured in revolutions per minute (RPM).

Faster drives generally equate to better performance, but they also generate more noise and heat. Excess heat cuts the life of hard drives dramatically. A rise of 5 degrees (Celsius) may reduce the life expectancy of a hard drive by as much as two years.

Hot systems get flaky and lock up at odd moments. Many things can impede the airflow—jumbled-up ribbon cables (used by older storage systems, USB headers, and other attachments), drives squished together in a tiny case, fans clogged by dust or animal hair, and so on.

Magnetic hard drives are manufactured in two standardized form factors, 2.5-inch and 3.5-inch (see Figure 8-4). A desktop system can use either form factor size; most laptops use the 2.5-inch form factor.

Figure 8-4 2.5-inch drive stacked on top of a 3.5-inch drive

The form factor only defines size.

Solid-State Drives

Booting up a computer takes time in part because a traditional hard drive needs to spin up before the read/write heads can retrieve data off the drive and load it into RAM.

All

In simple terms, SSDs use flash memory chips to store data instead of all those pesky metal spinning parts used in platter-based hard drives (see Figure 8-5).

EXAM TIP Although you can still buy mSATA cards as we go to print, the technology is definitely on its way out for both laptop and desktop computers, replaced by M.2. The latter standard is half the physical size and offers substantially better performance. The M.2 form factor is incorrectly referred to as M2 (with no dot) in CompTIA A+ 1001 exam objective 3.4. M.2 slots come in a variety, keyed for different sorts of mass storage uses. The keys have a letter associated. M.2 slots that use Key B, Key M, or Keys B+M support mass storage devices, for example, like in Figure 8-7. Other slots like Key A and Key E are used in wireless networking devices. The specifics of the keys are beyond the current A+ exam, but M.2 looks like it’s here to stay, so you need to be aware of the variations. SSDs use nonvolatile flash memory such as NAND that retains data when power is turned off or disconnected. (See Chapter 10, “Essential Peripherals,” for the scoop on flash memory technology.)

Cost

Less expensive SSDs ...

implement less reliable multi-level cell (MLC) memory technology in place of the more efficient single-level cel...

That process is hidden from the operating system by presenting an electronic façade to the OS that makes the SSD appear to be a traditional magnetic hard drive.

Performance Variables

Sequential Read/Write Performance

A common measure of a storage device’s top speed is its throughput,

or the...

at which it can read and write long sequ...

For context, traditional hard drives generally have sequential read/write speeds that top out at 200 MBps; SATA SSDs can hit 600 MBps; and NVMe SSDs roll at 2500 MBps or faster. These numbers are useful if you know your drives will frequently read and write huge files, but very few real-world systems do.

These measurements are all typically expressed as a number of input/output operations per second (IOPS),

MBps.

For context, traditional hard drives typically clock in at fewer than 150 IOPS, whereas the latest NVMe SSDs boas...

La...

It’s also useful to look at a drive’s response time, access time, or latency, which measures how quickly it responds to a single request. Latency is usually expressed in milliseconds (ms) or microseconds (µs). Low-latency storage is critical for high-performance file and databa...

For context, traditional hard drives often...

under 20 ms, whereas SSDs commonly clock in w...

The quality of the SSD matters for boot-up time and application load, but the machine will rarely break a sweat after that.

A workstation for high-end video editing, on the other hand, may read and write massive files for hours on end. A large file server may need to read and write thousands of tiny files a minute.