Cards also come in several thicknesses, which are meaningful only because a
slightly thicker card can hold more circuitry than a thinner one.
The most common card designs follow:
Type I.A 3.3mm-thick card, often used for RAM, flash memory, and
other simple devices.
Type II.A 5mm-thick card, used for more complex devices such as NIC
and WiFi cards. You can even buy a tiny hard drive that fits in this slot.
Type II slots can also accept thinner Type I cards.The PC Card specification was also intended to allow for two other forms:
Type III.A 10.5mm-thick card originally intended for use with removable
hard drives.Type IV.Not widely used, this design could accommodate thicker, more
complex, or multipurpose cards with more than one function.Newer and improved! USB 2.0...........................................................
Limits don’t last long in a hot high-tech market, and one of the most useful
barrier busters is the Universal Serial Bus. The USB opened up laptops (and
desktops) to almost limitless expansion that works from the outside in.
A modern laptop that includes a USB port (especially one that complies with
USB 2.0 or a later version of the standard) can easily work with small external
hard drives, CD or DVD drives, modems, network interfaces, wireless adapters,
audio cards, specialized video capture and output devices — just about any
expansion that can be applied to a PC of any size. USB was introduced in 1996,
and the considerably faster 2.0 version arrived in 2001.
Here’s the skinny on USB 2.0:
If your laptop has it, use it.If your laptop doesn’t have it, add it.
If your laptop offers the older, slower USB 1.1, upgrade to USB 2.0.The numbers tell the story: USB 2.0 is capable of moving data at a top speed
of 480 Mbps, with a promise of even faster speed in future versions. And it
gets better: A laptop (or a desktop) can connect as many as 127 devices in a
single chain.Best of all, each USB port used a single set of interrupts, direct
memory access (DMA),and memory resources no matter how many devices
are attached. DMA is a way to bypass the microprocessor when it is neces-
sary to transfer data from one location in memory to another.
Chapter 16: Breaking Out of the Box: PC Cards, USB, and FireWire 243