Information Technology Reference
In-Depth Information
Number
of
bits
transmitt
ed
per
operation
(bits)
Data
transfer
rate
(bps)
=
Transfer t
ime
per
operation
(s)
If operated with a fixed clock frequency for each operation then the data transfer rate (in
bits/second) will be
Data
transfer
rate
(bps)
=
Number
of
bits
transmitt
ed
per
operation
(bits)
·
Clocking
rate
(Hz)
For example, the ISA bus uses an 8 MHz (8·10
6
Hz) clocking frequency and has a 16-bit data
bus. Thus the maximum data transfer rate (in bps) will be:
6
6
Data
transfer
rate
=
16
·
8
·
10
=
128
·
10
b/s
=
128Mbps
Often it is required that the data rate is given in B/s, rather and bps. To convert from bps to
B/s, eight divides the bps value. Thus to convert 128Mbps to B/s
Data
transfer
rate
=
128Mbps
Example conversion from bps to B/s
128
=
Mbps
=
16MB/s
8
For serial communication, if the time to transmit a single bit is 104.167 ms then the maximum
data rate will be
Example conversion to bps for a serial
transmission with a given transfer time
interval
1
Data
transfer
rate
=
=
9600
bps
6
-
104.167
·
10
2.1.3 Address bus
The address bus is responsible for identifying the location into which the data is to be passed
into. Each location in memory typically contains a single byte (8 bits), but could also be ar-
ranged as words (16 bits), or long words (32 bits). Byte-oriented memory is the most flexible
as it also enables access to any multiple of eight bits. The size of the address bus thus indi-
cates the maximum addressable number of bytes. Table 2.3 shows the size of addressable
memory for a given address bus size. The number of addressable bytes is given by:
Addressable locations for a
given address bus size
n
Addressabl
e
locations
=
2
bytes
where
n
is the number of bits in the address bus. For example:
•
A 1-bit address bus can address up to two locations (that is 0 and 1).
A 2-bit address bus can address 2
2
or 4 locations (that is 00, 01, 10 and 11).
•
A 20-bit
address bus can address up to 2
20
addresses (1 MB).
•
A 32-bit
address bus can address up to 2
32
addresses (4 GB).
•
The units used for computers for defining memory are B (Bytes), kB (kiloBytes), MB
(megaBytes) and GB (gigabytes). These are defined as:
