Information Technology Reference
In-Depth Information
deeper into the EISA bus connector. It then makes connections with a 32-bit data and
address bus. An EISA card has twice the number of connections over an ISA card and
there are extra slots that allow it to be inserted deeper into the connector. The ISA card
only connects with the upper connectors because it has only a single key slot. EISA uses
a synchronous transfer at a clock speed of 8 MHz. It has a full 32-bit data and address
bus and can address up to 4 GB of memory. In theory the maximum transfer rate is 4
bytes for every clock cycle. As the clock runs at 8 MHz, the maximum data rate is
32 MB/s.
3.5
Comparison of different types
Data throughput depends on the number of bytes being communicated for each transfer and
the speed of the transfer. With the PC, ISA and EISA buses this transfer rate is fixed at 8
MHz, whereas the PCI and VL local buses use the system clock. For many applications the
ISA bus offers the best technology as it has been around for a long time, it gives a good data
throughput and it is relatively cheap and reliable. It has a 16-bit data bus and can thus trans-
fer data at a maximum rate of 16 MB/s. The EISA bus can transfer four bytes for each clock
cycle, thus if four bytes are transferred for each clock cycle, it will be twice as fast as ISA.
The maximum data rates for the different interface cards are:
PC
8 MB/s
ISA
16 MB/s
EISA
32 MB/s
VL-Local bus
132 MB/s
(33 MHz system clock using 32-bit transfers)
PCI
264 MB/s
(33 MHz system clock using 64-bit transfers)
MCA
20 MB/s
(160 MB/s burst)
The type of interface technology used depends on the data throughput. Table 3.2 shows some
typical transfer data rates. The heaviest usage on the system are microprocessor to memory
and graphics adaptor transfers. These data rates depend on the application and the operating
system used. Graphical user interface (GUI) programs have much greater data throughput
than programs running in text mode. Notice that a high specification sound card with re-
cording standard quality (16-bit samples at 44.1 kHz sampling rate) only requires a transfer
rate of 172 kB/s. The transfer rate for audio is:
Transfer
rate
(hi
-
fi)
=
Number
of
samples
per
second
·
Number
of
bytes
per
sample
(B/s)
=
(
44
100
·
2
·
2
B/s
=
176
400
B/s
166
400
=
=
172.26
kB/s
1024
A standard Ethernet local area network card transfers at data rates of up 10 Mbps (about
1 MB/s), although new fast Ethernet cards can transfer at data rates of up to 100 Mbps (about
10 MB/s). These transfers thus require local bus type interfaces.
