2.0 Laptop and Portable Devices
2.1 Identify the fundamental principles of using laptops and
A laptop computer is primarily intended to be portable. The
characteristics of a portable device are given below:
Lesser weight: People prefer to carry a laptop that weights,
say 5lb (approx. 2 kg) than one that weight 20lb (or 8 kg). A laptop
typically weighs less than 10 lbs compared to a typical desk top that weighs
Lesser power consumption: laptops consume much less power
compared to desk tops. Typically, a DC converter is used to feed DC power to
a laptop computer. The DC converter converts the AC power (US:110V, EU:220V)
to required DC voltage. An internal battery supplies power to the laptop
when there is no AC power available.
Rugged: All the components of a laptop are ruggedized to
enable safe transport from one place to another. A laptop consists of
smaller form factor assemblies that are ruggedized for both heat and
vibration. We will be discussing the sub-assemblies form factor at a later
Slim display: Usually all laptops have integrated LCD (or
TFT) display as compared to desk tops that have CRT displays. CRT displays
are bulkier and consumes more energy.
Integrated Keyboard and Mouse: A laptop has integrated
keyboard, and mouse. However, it is possible to connect external mouse and
keyboard for convenience on most of the laptops.
Functionally, there is no difference between a laptop and a
desktop computer. Both run same operating systems, and applications.
We now discuss the said characteristics of laptops in more
Laptops widely use
SO-DIMM (Small Outline Dual In-line Memory
Module), a smaller version of regular DIMM components used in desktops. The
figure below provides a comparison of SO-DIMM and a regular DIMM package:
Above: A regular 144-pin
Above: a 200-pin DDR
Above, 240-pin DDR2
As can be seen from the above figure, a SODIMM is roughly half the size of
a regular DIMM used in desktop computers.
SDRAM (Synchronous Dynamic Random Access Memory) has a synchronous
interface. It waits for a clock pulse before transferring data and is
therefore synchronous with the computer system bus and processor. This greatly
improved performance over asynchronous DRAM. Notebook SDRAM modules are
usually 144-pin SO-DIMMs, as shown in fingure above.
(DDR stands for Double Data Rate) sends and receives data twice
as often as SDRAM. This is achieved by transferring data on both the rising
edge and the falling edge of a clock cycle. DDR memory usually comes in the
form of a 200-pin DDR SO-DIMM (see image above).
Second generation DDR memory provides greater bandwidth and works on a
voltage of 1.8V instead of the 2.5V used by DDR memory modules, DDR2 consumes
less power than its predecessor, helping to extend notebook battery life. DDR2
memory modules are 240-pin DDR2 SO-DIMMs.
Memory Speed: Two factors are used for this measurement. 1. The operating
frequency and 2. the bandwidth. SDRAM rated PC100 and PC133 work at
100MHz and 133MHz and provide 800MB/s and 1066MB/s bandwidth respectively.
SDRAM and DDR/DDR2 SDRAM all use 8-byte (64bit) wide DIMM (transfer 8-byte
data per clock cycle).
DDR and DDR2 memory uses different notation. DDR266 memory works at 266MHz,
providing 2100MB/s bandwidth (Corresponding to the PC2100 designation). DDR400
memory is called PC3200 for its 3200MB/s bandwidth. The DDR2 533 is also
called PC2 4200 or PC2 4300 but 'PC2' is used here to refer to DDR2 instead.
DDR2 800 is the same as PC2 6400.
The bandwidth above is for single channel use. When memory is used in dual
channel mode, the bandwidth doubles - for instance, dual channel DDR400
provides 6400MB/s (or 6.4GB/s) bandwidth as opposed to 3200MB/s for single
Recommended Laptop Memory Size:
Mainstream Users: 512MB or more
A capacity of 512MB is the minimum required to run multiple simultaneous
current-day programs. A capacity of 256MB can sufficient for everyday
applications such as Web surfing, chatting, and office work.
Business Users: 1GB or more
If you often open and work on many large documents simultaneously, a
memory of 1GB is recommended for faster switching between applications as
most application data is stored in RAM instead of being accessed from the
hard drive every time it is needed (relatively slow).
Multimedia Users/Gamers: 1GB or more
A memory of 1GB is the recommended minimum if you play any latest games.
For multimedia processing tasks, which are similarly resource intensive, a
memory of 1GB is recommended.
Mobile Workstation Users: 2GB
Professional developers require as much memory as possible. Typical
applications involve image processing, video/audio editing, etc. A memory of
at least 2GB memory is recommended for smooth performance.
2. Laptop Hard disks:
Laptop hard disks primarily differ from that of desktop hard disks in size
and reliability. Given below are the important characteristics of laptop hard
A desktop computer has 3.5-inch drives, whereas a notebook computer, on the
other hand, has a smaller 2.5-inch or 1.8-inch notebook hard drive. 1.8”
hard drives are mainly installed and used in ultra-portable notebooks.
Like other notebook components, hard drive is specifically designed for
reduced power consumption. The average operating power consumption of a 7,200
RPM 3.5-inch internal hard drive currently exceeds 10 watts. A typical 7200
RPM notebook hard drive consumes about 2 watts by comparison.
Though current notebook hard drives spin at speeds of up to 5,400 RPM and
even 7,200 RPM, the noise-reduction technologies employed in current hard
drives mean that hard drives can run quetly.
Quite unlike desktop computers, notebook computers are often moved from one
place to another. To this end, enhanced vibration and shock protection are
important for laptop hard drives. A typical notebook computer hard drive can
take more than double the shock/vibration to that of a desktop hard drive.
Important specifications are given below:
Notebook hard drives offer capacities of over 100GB. Hard drives of
capacities 20GB, 40GB, 60GB, 80GB, 100GB, 120GB, 160GB and 200GB models are
The spindle speeds determines the performance of a hard drive. Most
of the notebooks have hard drives with 5,400 RPM. Other available speeds
include 7,200 RPM and 4,200 RPM drives. A 7,200RPM provides better performance
(at more power consumption), and a 4,200 RPM hard drive consumes less power
but offers slower performance level.
Hard drive cache helps to improve the performance by holding the data
temporarily for rapid access. A larger cache is recommended for better
performance of a hard drive. Notebook hard drives typically come with 2 MB,
8MB or 16MB cache options.
Two interface standards available with notebook hard drives are: 1.
parallel ATA (also known as IDE) and 2. serial ATA (known as SATA). Most
parallel ATA notebook hard drives follow the ATA-6 specification for 100MB/s
I/O throughput. SATA notebook hard drives follow SATA 150 for a throughput of
1.5 Gb/s (150MB/s), or SATA 3.0 Gb/s for a throughput of 3.0 Gb/s (300MB/s).
Two notebook hard drive form factors widely used are: 2.5-inch and
1.8-inch. The former is widely applied in most notebook types, while the
latter is typically found in ultra-thin notebooks. The thickness of hard
drives may differ. Therefore, even if you find a 2.5 inch hard drive is
recommended for your laptop, ensure that the thickness of the hard drive is
also complying the specified value. For example, a 2.5-inch hard drive with a
thickness of 12.5 mm is not suitable if your notebook will only hold a
2.5-inch hard drive that is 9.5mm thick.