The 8086 was the first x86 processor—Intel
had already released the 4004, the 8008, the 8080 and the
8085. This 16-bit processor could manage 1 MB of memory
using an external 20-bit address bus. The clock frequency
chosen by IBM (4.77 MHz) was fairly low, though the
processor was running at 10 MHz by the end of its career.
The first PCs used a derivative of this
processor, the 8088, which had only an 8-bit (external) data
bus. An interesting aside is that the control systems in the
US space shuttles use 8086 processors and NASA was forced to
buy some from
eBay in 2002 since Intel could no longer supply them.
Introduced June 8, 1978
Clock rates:
5 MHz with 0.33 MIPS
8 MHz with 0.66 MIPS
10 MHz with 0.75 MIPS
The memory is divided into odd and even banks; it
accesses both banks concurrently to read 16 bits of data
in one clock cycle
Bus Width 16 bits data, 20 bits address
Number of Transistors 29,000 at 3 µm
Addressable memory 1 megabyte
Up to 10X the performance of 8080
Used in portable computing, and in the IBM PS/2
Model 25 and Model 30. Also used in the AT&T PC6300 /
Olivetti M24, a popular IBM PC-compatible (predating the
IBM PS/2 line). Used segment registers to access
more than 64 KB of data at once, which many programmers
complained made their work excessively difficult.
8088
Introduced June 1, 1979
Clock rates:
5 MHz with 0.33 MIPS
8 MHz with 0.66 MIPS
Internal architecture 16 bits
External bus Width 8 bits data, 20 bits address
Number of Transistors 29,000 at 3 µm
Addressable memory 1 megabyte
Identical to 8086 except for its 8-bit external bus
(hence an 8 instead of a 6 at the end)
Used in IBM PCs and PC clones
80286
The 80286 was 3.6 times faster than the 8086 at the
same frequency. It could manage up to 16 MB of memory, but
the 286 was still a 16-bit processor. It was the first x86
equipped with a memory management unit (MMU), allowing it to
manage virtual memory. Like the 8086, it did not have a
floating-point unit (FPU), but could use a x87 co-processor
chip (80287). Intel offered these processors at a maximum
frequency of 12.5 MHz, whereas their competitors reached 25
MHz.
Introduced February 1, 1982
Clock rates:
6 MHz with 0.9 MIPS
8 MHz, 10 MHz with 1.5 MIPS
12.5 MHz with 2.66 MIPS
16 MHz, 20 MHz and 25 MHz available.
Bus Width: 16 bits data, 24 bits address.
Included memory protection hardware to support
multitasking operating systems with per-process address
space
Number of Transistors 134,000 at
1.5 µm
Addressable memory 16 MB
Added protected-mode features to 8086 with
essentially the same instruction set
3–6X the performance of the 8086
Widely used in IBM-PC AT and AT clones contemporary
to it
32-bit processors: the 80386 range
80386DX
Intel’s 80836 was the first x86 with a 32-bit
architecture. Several versions of this processor were
offered. The two best known are the 386 SX (Single-word
eXternal), which had a 16-bit data bus, and the 386 DX
(Double-word eXternal) with a 32-bit data bus. Two other
versions are worth noting, though: the SL, which was the
first x86 to offer management of a cache (external) and the
386EX, used in the space program (the Hubble telescope uses
this processor).
Introduced October 17, 1985
Clock rates:
16 MHz with 5 MIPS
20 MHz with 6 to 7 MIPS, introduced February 16,
1987
25 MHz with 7.5 MIPS, introduced April 4, 1988
33 MHz with 9.9 MIPS (9.4 SPECint92 on Compaq/i
16K L2), introduced April 10, 1989
Bus Width 32 bits data, 32 bits address
Number of Transistors 275,000 at 1 µm
Addressable memory 4 GB
Virtual memory 64
TB
First x86 chip to handle 32-bit data sets
Reworked and expanded memory protection support
including
paged virtual memory and virtual-86 mode, features
required at the time by
Xenix and Unix.
This memory capability spurred the development and
availability of OS/2 and is a fundamental requirement
for modern operating systems like
Linux,
Windows, and Mac OS.
Used in desktop computing
80386SX
Introduced June 16, 1988
Clock rates:
16 MHz with 2.5 MIPS
20 MHz with 3.1 MIPS, introduced January 25,
1989
25 MHz with 3.9 MIPS, introduced January 25,
1989
33 MHz with 5.1 MIPS, introduced October 26,
1992
Internal architecture 32 bits
External data bus width 16 bits
External address bus width 24 bits
Number of Transistors 275,000 at 1 µm
Addressable memory 16 MB
Virtual memory 32 GB
Narrower buses enable low-cost 32-bit processing
Used in entry-level desktop and portable computing
No Math Co-Processor
No commercial Software used for protected mode or
virtual storage for many years
80376
The Intel i376 is an embedded version of the
i386SX.
Introduced January 16, 1989; discontinued June 15,
2001
Variant of 386SX intended for embedded systems
No "real mode", starts up directly in "protected
mode"
Replaced by much more successful
80386EX from 1994
80386SL
Introduced October 15, 1990
Clock rates:
20 MHz with 4.21 MIPS
25 MHz with 5.3 MIPS, introduced September 30,
1991
Internal architecture 32 bits
External bus width 16 bits
Number of Transistors 855,000 at 1 µm
Addressable memory 4 GB
Virtual memory 1 TB
First chip specifically made for portable computers
because of low power consumption of chip
Highly integrated, includes cache, bus, and memory
controllers
80386EX
Introduced August 1994
Variant of 80386SX intended for
embedded systems
Static core, i.e. may run as slowly (and thus, power
efficiently) as desired, down to full halt
On-chip peripherals:
Clock and power management
Timers/counters
Watchdog timer
Serial I/O units (sync and async) and parallel
I/O
DMA
RAM refresh
JTAG test logic
Significantly more successful than the 80376
Used aboard several orbiting satellites and
microsatellites
){kind=link}
