-
The Pentium bus architecture is not this simple.
-
We will elaborate on this later.
-
Bus Architecture: Three buses:
-
Address:
-
If I/O, a value between 0000H and FFFFH is issued.
-
If memory, it depends on the architecture:
-
20
-bits (8086/8088)
-
24
-bits (80286/80386SX)
-
25
-bits (80386SL/SLC/EX)
-
32
-bits (80386DX/80486/Pentium)
-
36
-bits (Pentium Pro/II/III)
-
Data:
-
8
-bits (8088)
-
16
-bits (8086/80286/80386SX/SL/SLC/EX)
-
32
-bits (80386DX/80486/Pentium)
-
64
-bits (Pentium/Pro/II/III)
-
Control:
-
Most systems have at least 4 control bus connections (active low).
-
MRDC
(Memory ReaD Control),
MWRC
,
IORC
(I/O Read Control),
IOWC
.
-
Bus Standards:
-
ISA
(Industry Standard Architecture): 8 MHz
-
8-bit (8086/8088)
-
16-bit (80286-Pentium)
-
EISA
: 8 MHz
-
32-bit (older 386 and 486 machines).
-
PCI
(Peripheral Component Interconnect): 33 MHz
-
32-bit or 64-bit (Pentiums)
-
VESA
(Video Electronic Standards Association): Runs at processor speed.
-
32-bit or 64-bit (Pentiums)
-
Only disk and video. Competes with the PCI but is not popular.
-
Bus Standards:
-
USB
(Universal Serial Bus): 10 Mbps (extensions to 100Mbps)
-
Newest systems.
-
Serial connection to microprocessor.
-
For keyboards, the mouse, modems and sound cards.
-
To reduce system cost through fewer wires.
-
AGP
(Advanced Graphics Port): 66MHz
-
Newest systems.
-
Fast parallel connection: Across 64-bits for 533MB/sec.
-
For video cards.
-
To accommodate the new
DVD
(Digital Versatile Disk) players.
-
It is important to notice that these I/O addresses are NOT memory-mapped addresses on the 80x86 machines.
-
Special instructions (IN/OUT) are used to communicate to the I/O devices.
