From the KnowledgeBase
An Introduction to PC
Hardware
CPU Chip
One of the more highly visible aspects of a chip is the "clock speed." Clock
speed is defined as the speed at which a microprocessor executes instructions.
Every computer contains an internal clock that regulates the rate at which
instructions are executed and synchronizes all the various computer components.
The CPU requires a fixed number of clock ticks (or clock cycles) to execute
each instruction. The faster the clock, the more instructions the CPU can
execute per second.
Clock speeds are expressed in megahertz (MHz), 1 MHz being equal to 1 million
cycles per second. The CPUs of personal computers currently have clock speeds
of anywhere from 500 MHz to over 2,000 MHz, or 2 gigahertz. It's important
to note that the clock speed of a PowerPC chip cannot be directly compared
to an Athlon or a Pentium chip. Because the command set for Apple's PowerPC
chips is different, a smaller clock speed results in the same computing speed.
CPU is short for Central Processing Unit. As
its name implies, the CPU chip is the part of your computer which processes
data and makes calculations and is the most important element of the computer.
Consumer PCs are usually equipped with either a Pentium (Intel), Athlon (AMD)
or PowerPC (Apple, IBM, Motorola) chip.
Memory
An acronym for Read-Only Memory, ROM is computer memory on which data has
been prerecorded. Once data has been written onto a ROM chip, it cannot be
removed and can only be read. ROM retains its contents even when the computer
is turned off, so it is referred to as being nonvolatile.
An acronym for Random Access Memory, RAM is a type of computer memory that
can be accessed randomly; that is, any byte of memory can be accessed without
touching the preceding bytes. RAM is the most common type of memory found
in computers and other devices, such as printers. RAM is volatile, meaning
it loses its contents when the power is turned off.
The CPU can process information much faster than the RAM can send and receive
that information. The L2 cache, sometimes called the secondary memory cache,
helps to bridge that gap by caching some of the data which goes to the CPU;
when the CPU needs to access the data again, it can get it from the secondary
cache rather than having to wait to be fed by the RAM.
Slots
Make sure you understand the difference between slots, which are on the
motherboard, and bays, which are empty racks inside the computer tower. Bays
can be used for additional drives, such as ZIP drives, CD-ROM drives and
hard drives.
Slots are sockets on the motherboard into which
a card (such as a network card or video card) can be plugged, allowing you
to install optional equipment.
PCI (Peripheral Component Interconnect) is a standard developed by Intel
for connecting peripherals to the motherboard. PCI slots are faster than
ISA slots (see below), and therefore more appropriate for devices which involve
large data transfers. Most motherboards now come with 3 or 4 PCI
slots.
ISA (Industry Standard Architecture) slots predate PCI slots and have become
uncommon. They may be appropriate for slower devices and some motherboards
still have 1 or 2 ISA slots.
AGP (Accelerated Graphics Port) is a faster specification developed for graphics
data.
PCMCIA slots are usually found on laptops and are slots for PC cards (most
often a modem or ethernet card). In rough terms, you can think of a PCMCIA
slot as the laptop equivalent of the PCI slot for the desktop, although PC
cards can be used in many types of devices.
Ports
Serial and parallel ports are currently considered to be "legacy ports,"
since they use old technology for data transfer. Newer technology includes
the following:
External ports (which are linked to the motherboard)
allow users to connect devices such as scanners, printers, mice and
keyboards.
A serial port can be used to connect many types of devices. Data is transferred
to and from the device one bit at a time.
A parallel port usually has a 25-pin connector and is most often used to
connect local printers. Devices attached to a parallel port are capable of
receiving more than one bit of data at a time.
PS/2 ports are used to connect the mouse and the keyboard.
USB (Universal Serial Bus) is an external bus standard that supports data
transfer rates of 12 Mbps (12 million bits per second). A single USB port
can be used to connect up to 127 peripheral devices, such as mice, modems,
and keyboards. USB also supports Plug and Play installation and "hot plugging,"
meaning you do not have to shut down the computer in order to attach or detach
a device from the machine.
USB 2.0 is a new version of the USB specification. This new port is
backwards-compatible, allowing older USB 1.1 devices to connect and operate
without trouble. However, the new USB Hi-Speed ports support data transfer
rates of 480 Mbps, even faster than FireWire ports.
FireWire is a very fast external bus standard that supports data transfer
rates of up to 400 Mbps (400 million bits per second). The name FireWire
has actually been trademarked by Apple; FireWire is also known as IEEE 1394.
(IEEE stands for the Institute of Electrical and Electronics Engineers.)
A single 1394 port can be used to connect up to 63 external devices and is
much faster than USB 1.1. It supports both Plug and Play and hot plugging
and also provides power to peripheral devices.
ATA / IDE / DMA and SCSI
There are two types of interfaces which can
be used to connect the hard drive to the motherboard: ATA (or IDE) and
SCSI.
ATA, IDE, and DMA are different versions of the same interface. Short for
Integrated Device Electronics, IDE is a standard for transferring data between
drives and the motherboard. All of these acronyms can quickly become confusing,
but if you hear someone talking about an "ATA hard drive," be aware that
ATA, IDE and DMA are interchangeable for most intents and purposes, and that
all of these interfaces are the alternative to SCSI.
Short for Small Computer System Interface, and pronounced "scuzzy," SCSI
is a parallel interface standard which is faster than IDE, but also more
expensive. You will encounter SCSI again when learning about external ports
on Macintosh computers.
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