HowStuffWorks of the Day (13.11.2005): How Laptops Work

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Introduction to How Laptops Work

In a way, the skyrocketing popularity of laptop computers is ironic. Theyre completely portable, and they use less power and make less noise than desktop models. But, theyre often a little slower and have less graphics and sound processing power, although these differences can be too small for most users to notice.

Laptops are also more expensive than desktops. The price gap is closing, though - laptop prices are falling faster than desktop prices, and laptop PCs actually outsold desktop models for the first time in May of 2005.

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Laptops vs Desktops

Overall, laptop and desktop computers are very similar. They have the same basic hardware, software and operating systems. The primary difference is how their components fit together.

A desktop computer includes a motherboard, video card, hard drive and other components in a large case. The monitor, keyboard, and other peripherals connect wirelessly or with cables. Whether the case sits vertically or horizontally, it has lots of space for add-in cards, cables and air circulation.

A laptop, however, is much smaller and lighter than even the most compact PC tower. Its screen is an integrated part of the unit, as is its keyboard. Instead of a spacious case with lots of room for air circulation, a laptop uses a small, flat design in which all the pieces fit together snugly.

Because of this fundamental design difference and because of a laptop's inherent portability, components have to:

1) Fit into a compact space
2) Conserve power
3) Produce less heat than desktop components

Often, these differences make the components more expensive, which can contribute to higher laptop prices.

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Processor

The microprocessor, or CPU, works with the operating system to control the computer. It essentially acts as the computer's brain. The CPU produces a lot of heat, so a desktop computer uses circulating air, a fan and a heat sink -- a system of plates, channels and radiator fins used to draw heat off of the processor -- to cool off. Since a laptop has far less room for each of these cooling methods, its CPU usually:

Runs at a lower voltage and clock speed - This reduces heat output and power consumption but slows the processor down. Most laptops also run at a higher voltage and clock speed when plugged in, and at lower settings when using the battery.

Mounts to the motherboard without using pins - Pins and sockets take up a lot of room in desktop PCs. Some motherboard processors mount directly to the motherboard without the use of a socket. Others use a Micro-FCBGA (Flip Chip Ball Grid Array), which uses balls instead of pins. These designs save space, but in some cases mean that the processor cannot be removed from the motherboard for replacement or upgrading.

Has a sleep or slow-down mode - The computer and the operating system work together to reduce the CPU speed when the computer is not in use or when the processor does not need to run as quickly. The Apple G4 processor also prioritizes data to minimize battery drain.

Some laptops use desktop CPUs that are set to run at lower clock speeds. Although this can improve performance, these laptops typically run much hotter and have a significantly reduced battery life.

Laptops usually have small fans, heat sinks, heat spreaders or heat pipes to help dissipate the heat from the CPU. Some higher end laptop models reduce heat even further with liquid coolant kept in channels alongside the heat pipe. Also, most laptop CPUs are near the edge of the unit. This allows the fan to move the heat directly to the outside instead of across other components.

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Memory and Storage

A laptop's memory can make up for some of the reduced performance that comes from a slower processor. Some laptops have cache memory on or very near the CPU, allowing it to access data more quickly. Some also have larger busses, allowing data to move between the processor, motherboard and memory more quickly.

Laptops often use smaller memory modules to save space. Memory types used in laptops include:

1) Small Outline Dual Inline Memory Module (SODIMM)
2) Dual Data Rate Synchronous RAM (DDR SDRAM)
3) Single data rate Synchronous RAM (SDRAM)
4) Proprietary memory modules

Some laptops have upgradeable memory and feature removable panels for easy access to the memory modules.

Like a desktop, a laptop has an internal hard disk drive, which stores the operating system, applications and data files. However, laptops generally have less disk space than desktops. A laptop hard drive is also physically smaller than that of a desktop. In addition, most laptop hard drives spin more slowly than desktop hard drives, reducing both heat and power consumption.

Desktop computers have multiple bays for installing additional drives, such as CD and DVD ROM drives. However, space in a laptop is in much shorter supply. Many laptops use a modular design, allowing a variety of drives to fit in the same bay. These drives come in three different designations:

1) Hot Swappable - The computer can stay on while changing the drive.
2) Warm Swappable - The computer can stay on while changing the drive, but the corresponding bus (the path the drive uses to send data to the CPU) must be inactive.
3) Cold Swappable - The computer must be off during the swap.

In some cases, these drive bays are not just limited to drives but will also accept extra batteries.

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Graphics Processing, Display and Sound

A graphics processing unit (GPU) is a microprocessor that handles the calculations necessary for 3-D graphics rendering. Like a CPU, a GPU produces a lot of heat. Most laptops have graphics capability built into the motherboard or have smaller graphics cards with a GPU designed specifically for laptop use. GPU manufacturers ATI and nVidia both make GPUs specifically for laptops. Laptops frequently share memory between the CPU and the GPU, saving space and reducing power consumption.

Many people don't notice a laptop's reduced graphics performance. Laptops have plenty of processing power for Web surfing and productivity applications. However, they may struggle with the latest 3-D games. A few specialty laptops, designed for gaming enthusiasts, include more powerful GPUs and additional video memory.

A laptop displays its graphics on a liquid crystal display (LCD) screen. Most screens measure between 12 and 17 inches, and the size of the screen affects the overall size of the laptop. In addition, laptop screens can be:

1) Black-and-white (16 grayscale) or color (65,536 colors)
2) Active or passive matrix
3) Reflective or backlit

Active matrix displays have sharper images and are easier to read, and backlit screens are better for low-level lighting conditions.

Most laptops also have sound cards or integrated sound processing on the motherboard as well as small, built-in speakers. However, there is generally not enough space inside a laptop for a top-of-the-line sound card or a high-quality speaker. Gaming enthusiasts and audiophiles can supplement their laptops' sound capabilities with external sound controllers, which use USB or FireWire ports to connect to the laptop.

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User Interfaces

Like any computer, a laptop needs a way for users to communicate with it. Laptops have keyboards like desktop computers, but the keys are generally smaller and closer together. Many laptops also have a PS/2 or USB connection that people can use to connect a mouse. Most manufacturers also allow people to use a laptop without a mouse by providing a touchpad or a trackpoint.

There are several variations on the design of a touchpad, but the basic principle in all of them is the same. The touchpad has two layers of material. One layer responds to vertical movement while the other responds to horizontal movement. Different designs use wire-sensor grids, semi-conductive gel, electrodes or even tiny springs. In all cases, the pad tracks the movement of a finger and translates it to the movement of the mouse. Some models respond to tapping to simulate clicking the mouse button or allow people to scroll through documents by moving their finger along one vertical edge.

A common alternative to touchpads is Trackpoint devices, which were introduced on IBM laptops. Trackpointers are tiny rubber sensors located between the G, B and H keys on the keyboard. Sensors under the trackpoint translate pressure to the movement of a mouse. Using a system called negative inertia, the cursor feels like it has a natural and comfortable weight when moved by a trackpointer. This makes using a trackpointer a little easier to get used to if you normally use a mouse.

The trackpoint sensor detects changes in the force, predicting changes in direction, and acting accordingly. This result is a quicker response from the cursor than is typical in a touchpad interface.

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Docking and Port Replicators

Many people in the professional world use laptop computers exclusively. This essentially makes their office portable. But spending hours a day in front of a laptop computer with a small keyboard and screen can become tremendously uncomfortable. Many people prefer traditional keyboards, mice and monitors for long sessions. Another limitation of laptops is the available number of ports and slots for additional components. Port replicators and docking stations offer a solution to these issues.

A port replicator is a piece of hardware that connects to the laptop and adds connections for other devices. It gives a laptop all of the connectivity of a desktop computer. The laptop then acts as a desktop tower, allowing people to work with a standard mouse, keyboard and monitor.

Docking stations take this one step further by adding PCI slots and other bays for peripherals traditionally reserved for desktop computers. They also have dedicated power supplies. A docking station virtually eliminates the differences between laptop and desktop computers.

A laptop doesn't have to have a port replicator or a docking station to support added peripherals like printers and mice. Laptops have many of the same types of connections as desktop computers. The devices have the same hot, warm and cold designations as swappable drives. Users can plug in and use any device that is compatible with the ports on the laptop. The limit to these additions is the number of ports on the computer.

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Power Supply

Laptops and desktops both run on electricity. Both have small batteries to maintain the real-time clock and, in some cases, CMOS RAM. However, unlike a desktop computer, a laptop is portable and can run on batteries alone.

Nickel-Cadmium (NiCad) batteries were the first type of battery commonly used in laptop computers, and older laptops sometimes still use them. They have a life of roughly two hours between charges, but this life decreases with each charge based on the memory effect. Gas bubbles form in the cell plates, reducing the total amount of available cell space for recharge. The only way around this is to discharge the battery completely before recharging it. The other drawback of NiCad is that if the battery charges too long, it can explode.

Nickel-Metal Hydride (NiMH) batteries are the bridge between NiCad and the newer Lithium-Ion (LiIon) batteries. They last longer between charges than NiCad but overall have a shorter total lifespan. They suffer from the memory effect, but to a lesser extent than NiCad batteries.

LiIon batteries are the current standard for laptop computers. They are light and have long life spans. They do not suffer from the memory effect, can be charged randomly, and won't overheat if overcharged. They are also thinner than any other battery available for laptops, making them ideal for the new ultra-thin notebooks. LiIon batteries can last for anything from about 950 up to 1200 charges.

Many laptops with LiIon batteries claim to have a 5-hour battery life, but this measurement can vary greatly depending on how the computer is used. The hard drive, other disk drives and LCD display all use substantial battery power. Even maintaining wireless Internet connectivity requires some battery power. Many laptop computer models have power management software to extend the battery life or conserve battery power when the battery is low.

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Whitebooks

Many people build custom PCs for themselves or customers. These home-made computers, called whiteboxes, represent a significant portion of the computer market. Some people also modify their computers for cosmetics or performance. This is called modding. But what about building or modding a laptop?

A modded or homemade laptop is called a whitebook. Whitebooks represent about 5 percent of the notebook market right now, and this number is slowly rising. The industry has done a pretty good job of keeping end users out of laptops. They've made it difficult to open, modify and get parts for a laptop. In addition, opening the laptop chassis voids the manufacturer's warranty in most cases.

It is still difficult to find parts to build a laptop from the ground up, but vendors like ASUS and ECS allow some customers to order blank laptop shells. They are especially open to resellers who build whitebooks and sell them to customers. In addition, people can mod or upgrade what came with the shell. Companies like TechStyle have made a business of it.

A laptop shell consists of:

* Chassis
* Motherboard
* Optical drive
* Display
* Keyboard
* Graphics Card

This means that anyone wanting to build a whitebook must find:

* Microprocessor
* RAM
* Wireless card

At this point, there are no real standards for the form factor (shape and design) of laptop parts. Processors designed for laptops are available for sale, but finding a motherboard for those chips is a different story. Hard drives are pretty standard, and SODIMM system memory is easy to come by, but other parts may take some digging.

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Laptop History

In the 1970s, Alan Kay of the Xerox Palo Alto Research Center had a vision for a wireless portable computer roughly the size of a notebook. He called it the Dynabook. Kay's Dynabook never got past sketches and a cardboard model, but it set the wheels in motion for the development of a truly portable computer.

In 1979, William Moggridge of Grid Systems Corporation created the first functioning portable computer: The Grid Compass Computer 1109. It had 340 kilobytes of bubble memory, a die-cast magnesium case and a folding electroluminescent graphics display screen. NASA bought a handful of them at $800 apiece for use in the space program.

Other companies, like Gavilan Computer and Apple, introduced other portable computers in following years. The first commercially viable machine, however, was the IBM PC Convertible, introduced in 1986. The PC Convertible featured:

* An 8088 microprocessor
* 256 kilobytes of memory
* Two 3.5-inch (8.9-cm) floppy drives
* An LCD display
* Parallel and serial printer ports
* Space for an internal modem
* A software suite including basic word processing, appointment calendar, telephone/address book, and calculator software

Weighing in at a hefty 12 lbs (5.4 kg), the PC Convertible sold for $3,500. It was the first portable computer with the clamshell design used in today's laptops. The success of the PC Convertible was the catalyst for competitors like Compaq and Toshiba to switch to the clamshell design in their portable computers. And so began the era of the laptop computer.

M©+square SG

Interesting Article.

I feel that this should have been in IT forum. Embarassed Mr. Green

Thanks anyway!

Cheers