Data is constantly being transferred within a computer and between computers.
But how much data, and how fast is it being computed? Data transfer is known as
bandwidth, which specifies how much data is being sent per second. The speed at
which data is computed is known as Hertz, which also dictates the frequency used
to transfer data.



Bandwidth
Other than bits and bytes and their multiples, probably the second most significant
concept to understand about computer measurements is bandwidth, also known as
data transfer rate. Bandwidth refers to the amount of information that can be sent
or received through a computer or network connection in one second. This can be
measured in bits (with a lower case b) or bytes (with an upper case B). For example,
the bandwidth of a USB 1.1 port running at full speed transfers a maximum of 11
megabits per second (11 Mbps, notice the lower case b), while the bandwidth of a
USB 2.0 port running at high speed is 480 Mbps, and a user might download 300 kilobytes (300 KB/s, notice the upper case B) of data per second. Or an expansion
card that goes into a PCI slot could transfer a maximum of 266 MB/s.
Bandwidth measurements like this are used for measuring the performance of serial,
parallel, wired and wireless network connections, expansion slots (PCI, PCIe,
and AGP), hard disk interfaces (PATA and SATA), and multipurpose device interfaces
(SCSI, USB, and FireWire). It defines the amount of information that can
flow through the computer.
Information flows through the computer in many ways. The CPU is the central
point for most information. When you start a program, the CPU instructs the
storage device to load the program into RAM. When you create data and print it,
the CPU instructs the printer to output the data.
Because of the different types of devices that send and receive information, two
major types of data transfers take place within a computer: parallel and serial.


Parallel Information Transfers
Parallel transfers use multiple “lanes” for data and programs, and in keeping with the
8 bits = 1 byte nature of computer information, most parallel transfers use multiples
of 8. Parallel transfers take place between the following devices:
■ Processor (CPU) and RAM
■ Processor (CPU) and interface cards
■ LPT (printer) port and parallel printer
■ SCSI port and SCSI devices
■ PATA /IDE host adapter and PATA/IDE drives
■ RAM and interface cards, either via the CPU or directly with direct memory access
(DMA)