![]() ![]() An Intel i386DX 16 MHz processor with a gray ceramic heat spreader | |
General information | |
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Launched | October 1985 |
Discontinued | September 28, 2007 [1] |
Common manufacturers |
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Performance | |
Max. CPU clock rate | 12.5 MHz to 40 MHz |
Data width | 32 bits (386SX: 16 bits) |
Address width | 32 bits (386SX: 24 bits) |
Architecture and classification | |
Technology node | 1.5 μm to 1 μm |
Instruction set | x86-16, IA-32 |
Physical specifications | |
Transistors | |
Co-processor |
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Package | |
Socket | |
Models |
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History | |
Predecessor | Intel 80286 |
Successor | i486 |
Support status | |
Unsupported |
The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor designed by Intel. The first pre-production samples of the 386 were released to select developers in 1985, while mass production commenced in 1986. The processor was a significant evolution in the x86 architecture, extending a long line of processors that stretched back to the Intel 8008. The 386 was the central processing unit (CPU) of many workstations and high-end personal computers of the time. The 386 began to fall out of public use starting with the release of the i486 processor in 1989, while in embedded systems the 386 remained in widespread use until Intel finally discontinued it in 2007.
Compared to its predecessor the Intel 80286, the 80386 added a three-stage instruction pipeline which it brings up to total of 6-stage instruction pipeline, extended the architecture from 16-bits to 32-bits, and added an on-chip memory management unit. This paging translation unit made it much easier to implement operating systems that used virtual memory. It also offered support for register debugging.
The 80386 featured three operating modes: real mode, protected mode and virtual mode. The protected mode, which debuted in the 80286, was extended to allow the 386 to address up to 4 GB of memory. With the addition of segmented addressing system, it can expand up to 64 terabytes of virtual memory. The all new virtual 8086 mode (or VM86) made it possible to run one or more real mode programs in a protected environment, although some programs were not compatible.
The 32-bit i386 can correctly execute most code intended for the earlier 16-bit processors such as 8086 and 80286 that were ubiquitous in early PCs. As the original implementation of the 32-bit extension of the 80286 architecture, [lower-alpha 1] the i386 instruction set, programming model, and binary encodings are still the common denominator for all 32-bit x86 processors, which is termed the i386 architecture, x86, or IA-32 , depending on context. Over the years, successively newer implementations of the same architecture have become several hundreds of times faster than the original 80386 (and thousands of times faster than the 8086). [lower-alpha 2]
Development of i386 technology began in 1982 under the internal name of P3. [4] The tape-out of the 80386 development was finalized in July 1985. [4] The 80386 was introduced as pre-production samples for software development workstations in October 1985. [5] Manufacturing of the chips in significant quantities commenced in June 1986, [6] [7] along with the first plug-in device that allowed existing 80286-based computers to be upgraded to the 386, the Translator 386 by American Computer and Peripheral. [8] [9] Mainboards for 80386-based computer systems were cumbersome and expensive at first, but manufacturing was justified upon the 80386's mainstream adoption. The first personal computer to make use of the 80386 was the Deskpro 386, designed and manufactured by Compaq; [10] this marked the first time a fundamental component in the IBM PC compatible de facto standard was updated by a company other than IBM.
The first versions of the 386 had 275,000 transistors. [2] The 20 MHz version operates at 4–5 MIPS. It also performs between 8,000 and 9,000 Dhrystones per second. [11] The 25 MHz 386 version was capable of 7 MIPS. [12] A 33 MHz 80386 was reportedly measured to operate at about 11.4 and 11.5 MIPS. [13] [14] At that same speed, it has the performance of 8 VAX MIPS. [15] These processors were running about 4.4 clocks per instruction. [16]
In May 2006, Intel announced that i386 production would stop at the end of September 2007. [17] Although it had long been obsolete as a personal computer CPU, Intel and others had continued making the chip for embedded systems. Such systems using an i386 or one of many derivatives are common in aerospace technology and electronic musical instruments, among others. Some mobile phones also used (later fully static CMOS variants of) the i386 processor, such as the BlackBerry 950 [18] and Nokia 9000 Communicator. Linux continued to support i386 processors until December 11, 2012, when the kernel cut 386-specific instructions in version 3.8. [19]
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The processor was a significant evolution in the x86 architecture, and extended a long line of processors that stretched back to the Intel 8008. The predecessor of the 80386 was the Intel 80286, a 16-bit processor with a segment-based memory management and protection system. The 80386 added a three-stage instruction pipeline which it brought up to total of 6-stage instruction pipeline, extended the architecture from 16-bits to 32-bits, and added an on-chip memory management unit. [20] This paging translation unit made it much easier to implement operating systems that used virtual memory. It also offered support for register debugging.
The 80386 featured three operating modes: real mode, protected mode and virtual mode. The protected mode, which debuted in the 286, was extended to allow the 386 to address up to 4 GB of memory. With the addition of segmented addressing system, it can expand up to 64 terabytes of virtual memory. [21] The all new virtual 8086 mode (or VM86) made it possible to run one or more real mode programs in a protected environment, although some programs were not compatible. It features scaled indexing and 64-bit barrel shifter. [22]
The ability for a 386 to be set up to act like it had a flat memory model in protected mode despite the fact that it uses a segmented memory model in all modes was arguably the most important feature change for the x86 processor family until the AMD released x86-64 in 2003.
Several new instructions have been added to 386: BSF, BSR, BT, BTS, BTR, BTC, CDQ, CWDE, LFS, LGS, LSS, MOVSX, MOVZX, SETcc, SHLD, SHRD.
Two new segment registers have been added (FS and GS) for general-purpose programs. The single Machine Status Word of the 286 grew into eight control registers CR0–CR7. Debug registers DR0–DR7 were added for hardware breakpoints. New forms of the MOV instruction are used to access them.
The chief architect in the development of the 80386 was John H. Crawford. [23] He was responsible for extending the 80286 architecture and instruction set to 32-bits, and then led the microprogram development for the 80386 chip.
The i486 and P5 Pentium line of processors were descendants of the i386 design.
The following data types are directly supported and thus implemented by one or more i386 machine instructions; these data types are briefly described here. [24] :
The following i386 assembly source code is for a subroutine named _strtolower
that copies a null-terminated ASCIIZ character string from one location to another, converting all alphabetic characters to lower case. The string is copied one byte (8-bit character) at a time.
00000000 55 00000001 89E5 00000003 8B750C 00000006 8B7D08 00000009 FC 0000000A AC 0000000B 3C41 0000000D 7C06 0000000F 3C5A 00000011 7F02 00000013 0420 00000015 AA 00000016 84C0 00000018 75F0 0000001A 5D 0000001B C3 | ; _strtolower:; Copy a null-terminated ASCII string, converting; all alphabetic characters to lower case.;; Entry stack parameters; [ESP+8] = src, Address of source string; [ESP+4] = dst, Address of target string; [ESP+0] = Return address;_strtolowerprocpushebp; Set up the call framemovebp,espmovesi,[ebp+0xc]; Set ESI = srcmovedi,[ebp+0x8]; Set EDI = dstcld; Auto-increment ESI and EDIagain:lodsb; Load AL from [src] and increment ESIcmpal,'A'; If AL < 'A',jlcopy; Skip conversioncmpal,'Z'; If AL > 'Z',jgcopy; Skip conversionaddal,'a'-'A'; Convert AL to lowercasecopy:stosb; Store AL to [dst]testal,al; If AL != 0,jnzagain; Repeat the looppopebp; Restore the previous callret; Return to callerendproc |
The example code uses the EBP (base pointer) register to establish a call frame, an area on the stack that contains all of the parameters and local variables for the execution of the subroutine. This kind of calling convention supports reentrant and recursive code and has been used by Algol-like languages since the late 1950s. A flat memory model is assumed, specifically, that the DS and ES segments address the same region of memory.
The first PC based on the Intel 80386 was the Compaq Deskpro 386. By extending the 16/24-bit IBM PC/AT standard into a natively 32-bit computing environment, Compaq became the first company to design and manufacture such a major technical hardware advance on the PC platform. IBM was offered use of the 80386, but had manufacturing rights for the earlier 80286. IBM therefore chose to rely on that processor for a couple more years. The early success of the Compaq Deskpro 386 played an important role in legitimizing the PC "clone" industry and in de-emphasizing IBM's role within it. The first computer system sold with the 386SX was the Compaq Deskpro 386S, released in July 1988. [26]
Prior to the 386, the difficulty of manufacturing microchips and the uncertainty of reliable supply made it desirable that any mass-market semiconductor be multi-sourced, that is, made by two or more manufacturers, the second and subsequent companies manufacturing under license from the originating company. The 386 was for a time (4.7 years) only available from Intel, since Andy Grove, Intel's CEO at the time, made the decision not to encourage other manufacturers to produce the processor as second sources. This decision was ultimately crucial to Intel's success in the market.[ citation needed ] The 386 was the first significant microprocessor to be single-sourced. Single-sourcing the 386 allowed Intel greater control over its development and substantially greater profits in later years.
AMD introduced its compatible Am386 processor in March 1991 after overcoming legal obstacles, thus ending Intel's 4.7-year monopoly on 386-compatible processors. From 1991 IBM also manufactured 386 chips under license for use only in IBM PCs and boards.
Intel originally intended for the 80386 to debut at 16 MHz. However, due to poor yields, it was instead introduced at 12.5 MHz. [27]
Early in production, Intel discovered a marginal circuit that could cause a system to return incorrect results from 32-bit multiply operations. Not all of the processors already manufactured were affected, so Intel tested its inventory. Processors that were found to be bug-free were marked with a double sigma (ΣΣ), and affected processors were marked "16 BIT S/W ONLY". [28] These latter processors were sold as good parts, since at the time 32-bit capability was not relevant for most users. [29]
The i387 math coprocessor was not ready in time for the introduction of the 80386, and so many of the early 80386 motherboards instead provided a socket and hardware logic to make use of an 80287. In this configuration the FPU operated asynchronously to the CPU, usually with a clock rate of 10 MHz. The original Compaq Deskpro 386 is an example of such design. However, this was an annoyance to those who depended on floating-point performance, as the performance advantages of the 80387 over the 80287 were significant. [ citation needed ]
Intel later offered a modified version of its 486DX in i386 packaging, branded as the Intel RapidCAD. This provided an upgrade path for users with i386-compatible hardware. The upgrade was a pair of chips that replaced both the i386 and i387. Since the 486DX design contained an FPU, the chip that replaced the i386 contained the floating-point functionality, and the chip that replaced the i387 served very little purpose. However, the latter chip was necessary in order to provide the FERR signal to the mainboard and appear to function as a normal floating-point unit.
Third parties offered a wide range of upgrades, for both SX and DX systems. The most popular ones were based on the Cyrix 486DLC/SLC core, which typically offered a substantial speed improvement due to its more efficient instruction pipeline and internal L1 SRAM cache. The cache was usually 1 KB, or sometimes 8 KB in the TI variant. Some of these upgrade chips (such as the 486DRx2/SRx2) were marketed by Cyrix themselves, but they were more commonly found in kits offered by upgrade specialists such as Kingston, Evergreen Technologies and Improve-It Technologies. Some of the fastest CPU upgrade modules featured the IBM SLC/DLC family (notable for its 16 KB L1 cache), or even the Intel 486 itself. Many 386 upgrade kits were advertised as being simple drop-in replacements, but often required complicated software to control the cache or clock doubling. Part of the problem was that on most 386 motherboards, the A20 line was controlled entirely by the motherboard with the CPU being unaware, which caused problems on CPUs with internal caches.
Overall, it was very difficult to configure upgrades to produce the results advertised on the packaging, and upgrades were often not very stable or not fully compatible.
Original version, released in October 1985. The 16 MHz version was available for 299 USD in quantities of 100. [30] The 20 MHz version was available for US$599 in quantities of 100. [11] The 33 Mhz version was available on April 10, 1989. [15]
The military version was made using the CHMOS III process technology. It was made to withstand 105 Rads (Si) or greater. It was available for US$945 each in quantities of 100. [32]
In 1988, Intel introduced the 80386SX, most often referred to as the 386SX, a cut-down version of the 80386 with a 16-bit data bus, mainly intended for lower-cost PCs aimed at the home, educational, and small-business markets, while the 386DX remained the high-end variant used in workstations, servers, and other demanding tasks. The CPU remained fully 32-bit internally, but the 16-bit bus was intended to simplify circuit-board layout and reduce total cost. [lower-alpha 3] The 16-bit bus simplified designs but hampered performance. Only 24 pins were connected to the address bus, therefore limiting addressing to 16 MB, [lower-alpha 4] but this was not a critical constraint at the time. Performance differences were due not only to differing data-bus widths, but also due to performance-enhancing cache memories often employed on boards using the original chip. This version can run the 32-bit application software at 70 to 90 percent compare to the regular Intel386 DX CPU. [33]
The original 80386 was subsequently renamed i386DX to avoid confusion. However, Intel subsequently used the "DX" suffix to refer to the floating-point capability of the i486DX. The 387SX was an 80387 part that was compatible with the 386SX (i.e. with a 16-bit databus). The 386SX was packaged in a surface-mount QFP and sometimes offered in a socket to allow for an upgrade.
The 16 MHz 386SX contains the 100-lead BQFP. It was available for USD $165 in quantites of 1000. It has the performance of 2.5 to 3 MIPS as well. [12] The low-power version was available on April 10, 1989. This version that uses 20 to 30 percent less power and has higher operating temperature up to 100 °C than the regular version. [15]
The 80386SL was introduced as a power-efficient version for laptop computers. The processor offered several power-management options (e.g. SMM), as well as different "sleep" modes to conserve battery power. [34] It also contained support for an external cache of 16 to 64 KB. The extra functions and circuit implementation techniques caused this variant to have over 3 times as many transistors as the i386DX. The i386SL was first available at 20 MHz clock speed, [35] with the 25 MHz model later added. [36] With this system, it reduced up to 40% foot space than the Intel386 SX system. That translate to lighter and more portable cost-effective system. [37]
Dave Vannier, the chief architect designed this microprocessor. It took them two years to complete this design since it uses the existing 386 architecture to implement. That assist with advanced computer-aided design tools which includes a complete simulation of system board. This die contains the 386 CPU core, AT Bus Controller, Memory Controller, Internal Bus Controller, Cache Control Logic along with Cache Tag SRAM and Clock. This CPU contains 855,000 transistors using one-micron CHMOS IV technology. It was available for USD $176 in 1,000 unit in quantities. [3] The 25-MHz version was available in samples for USD $189 in 1,000-piece quantities, but that version will be available in production by end of 1991. [38] It supports up to 32 Megabytes of physical address space. [39] [40]
In May 1991, Intel introduced an upgrade for IBM PS/2 Model 50 and 60 systems which contain 80286 microprocessors, converting them to full blown 32-bit systems. The SnapIn 386 module is a daughtercard with 20-MHz 386SX and 16-Kbyte direct-mapped cache SRAM memory. It directly plugs into the existing 286 socket with no cables, jumpers or switches. In the winter of 1992, an additional to this module now supported to IBM PS/2 Model 50 Z, 30 286 and 25 286 systems. Both modules were available for USD $495. [41] [42]
A specially packaged Intel 486DX and a dummy floating-point unit (FPU) designed as pin-compatible replacements for an i386 processor and i387 FPU.
This was an embedded version of the 80386SX which did not support real mode and paging in the MMU.
System and power management and built in peripheral and support functions: Two 82C59A interrupt controllers; Timer, Counter (3 channels); Asynchronous SIO (2 channels); Synchronous SIO (1 channel); Watchdog timer (Hardware/Software); PIO. Usable with 80387SX or i387SL FPUs.
Transparent power management mode, integrated MMU and TTL compatible inputs (only 386SXSA). Usable with i387SX or i387SL FPUs.
Transparent power management mode and integrated MMU. Usable with i387SX or i387SL FPUs.
Windows 95 was the only entry in the Windows 9x series to officially support the 386, requiring at least a 386DX, though a 486 or better was recommended; [43] Windows 98 requires a 486DX or higher. [44] In the Windows NT family, Windows NT 3.51 was the last version with 386 support. [45] [46]
Debian GNU/Linux dropped 386 support with the release of 3.1 (Sarge) in 2005 and completely removed support in 2007 with 4.0 (Etch). [47] [48] Citing the maintenance burden around SMP primitives, the Linux kernel developers cut support from the development codebase in December 2012, later released as kernel version 3.8. [19]
Among the BSDs, FreeBSD's 5.x releases were the last to support the 386; support for the 386SX was cut with release 5.2, [49] while the remaining 386 support was removed with the 6.0 release in 2005. [50] OpenBSD removed 386 support with version 4.2 (2007), [51] DragonFly BSD with release 1.12 (2008), [52] and NetBSD with the 5.0 release (2009). [53]
The Intel 80286 is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non-multiplexed address and data buses and also the first with memory management and wide protection abilities. The 80286 used approximately 134,000 transistors in its original nMOS (HMOS) incarnation and, just like the contemporary 80186, it can correctly execute most software written for the earlier Intel 8086 and 8088 processors.
The 8086 is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus, and is notable as the processor used in the original IBM PC design.
The Intel 8088 microprocessor is a variant of the Intel 8086. Introduced on June 1, 1979, the 8088 has an eight-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers and the one megabyte address range are unchanged, however. In fact, according to the Intel documentation, the 8086 and 8088 have the same execution unit (EU)—only the bus interface unit (BIU) is different. The 8088 was used in the original IBM PC and in IBM PC compatible clones.
The Intel 486, officially named i486 and also known as 80486, is a microprocessor. It is a higher-performance follow-up to the Intel 386. The i486 was introduced in 1989. It represents the fourth generation of binary compatible CPUs following the 8086 of 1978, the Intel 80286 of 1982, and 1985's i386.
The Intel 80186, also known as the iAPX 186, or just 186, is a microprocessor and microcontroller introduced in 1982. It was based on the Intel 8086 and, like it, had a 16-bit external data bus multiplexed with a 20-bit address bus. The 80188 variant, with an 8-bit external data bus was also available.
The Pentium is a x86 microprocessor introduced by Intel on March 22, 1993. It is the first CPU using the Pentium brand. Considered the fifth generation in the 8086 compatible line of processors, its implementation and microarchitecture was internally called P5.
x86 is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088. The 8086 was introduced in 1978 as a fully 16-bit extension of 8-bit Intel's 8080 microprocessor, with memory segmentation as a solution for addressing more memory than can be covered by a plain 16-bit address. The term "x86" came into being because the names of several successors to Intel's 8086 processor end in "86", including the 80186, 80286, 80386 and 80486. Colloquially, their names were "186", "286", "386" and "486".
The Am386 CPU is a 100%-compatible clone of the Intel 80386 design released by AMD in March 1991. It sold millions of units, positioning AMD as a legitimate competitor to Intel, rather than being merely a second source for x86 CPUs.
Intel's i960 was a RISC-based microprocessor design that became popular during the early 1990s as an embedded microcontroller. It became a best-selling CPU in that segment, along with the competing AMD 29000. In spite of its success, Intel stopped marketing the i960 in the late 1990s, as a result of a settlement with DEC whereby Intel received the rights to produce the StrongARM CPU. The processor continues to be used for a few military applications.
The Cyrix Cx486SLC is a x86 microprocessor that was developed by Cyrix. It was one of Cyrix's first CPU offerings, released after years of selling math coprocessors that competed with Intel's units and offered better performance at a comparable or lower price. It was announced in March of 1992, and released 2 months later in May, with a price of $119. It was priced competitively against the Intel 486SX, causing Intel to lower the price of their chip from $286 to $119 in just days.
x87 is a floating-point-related subset of the x86 architecture instruction set. It originated as an extension of the 8086 instruction set in the form of optional floating-point coprocessors that work in tandem with corresponding x86 CPUs. These microchips have names ending in "87". This is also known as the NPX. Like other extensions to the basic instruction set, x87 instructions are not strictly needed to construct working programs, but provide hardware and microcode implementations of common numerical tasks, allowing these tasks to be performed much faster than corresponding machine code routines can. The x87 instruction set includes instructions for basic floating-point operations such as addition, subtraction and comparison, but also for more complex numerical operations, such as the computation of the tangent function and its inverse, for example.
CHMOS refers to one of a series of Intel CMOS processes developed from their HMOS process. CHMOS stands for "complementary high-performance metal-oxide-silicon. It was first developed in 1981.
The Intel 80387SX is the math coprocessor, also called an FPU, for the Intel 80386SX microprocessor. Introduced in 1987, it was used to perform floating-point arithmetic operations directly in hardware. The coprocessor was designed only to work with the 386SX, rather than the standard 386DX. This was because the original 80387 could not communicate with the altered 16 bit data bus of the 386SX, which was modified from the original 386DX's 32 bit data bus. The 387SX uses a 68-pin PLCC socket, just like some variants of the 80286 and the less common 80186 CPU, and was made in speeds ranging from 16 MHz to 33 MHz, matching the clock speed range of the Intel manufactured 386SX. Some chips like the IIT 3C87SX could get up to 40 MHz, matching the clock speeds of the fastest 386SX CPUs.
During the late 1980s, Intel sold two ISA expansion cards named Intel Inboard 386/AT and Intel Inboard 386/PC, which allowed users to upgrade an IBM AT or an IBM PC respectively. The boards allowed users to upgrade their machines' CPU to a 16 MHz 80386 processor. Both variants utilized a ribbon cable which plugged into the computer's original CPU socket on one end and into a socket on the Inboard card on the other end.
The Compaq Deskpro is a line of business-oriented desktop computers manufactured by Compaq, then replaced by the Evo brand in 2001. Models were produced containing microprocessors from the 8086 up to the x86-based Intel Pentium 4.
The 386SLC is an Intel-licensed version of the 386SX, developed and manufactured by IBM in 1991. It included power-management capabilities and an 8KB internal CPU cache, which enabled it to yield comparable performance to 386DX processors of the same clock speed, which were considerably more expensive. Known inside IBM as "Super Little Chip" for its initials, it was used in the IBM PS/2 35, 40 and 56 Series and in the IBM PS/ValuePoint 325T, but never gained much market share. This was mainly due to an agreement with Intel, in which IBM was not allowed to sell their CPUs if they were not part of a system or upgrade board. It was also marketed as an optional upgrade for 8086-equipped IBM PS/2 25 Series computers.
The Deskpro 386 is a line of desktop computers in Compaq's Deskpro range of IBM PC compatibles. Introduced in September 1986, the Deskpro 386 was the first personal computer to feature Intel's 32-bit 80386 microprocessor. It also marks the first time that a major component of the IBM Personal Computer de facto standard was updated by a company other than IBM themselves—in this case, upgrading from the 80286 processor of the Personal Computer/AT.
American Computer & Peripheral, Inc. (AC&P), also written as American Computer and Peripheral, was an American computer company based in Santa Ana, California. The company was founded in 1985 by Alan Lau and released several expansion boards for the IBM PC as well as a few PC clones before going bankrupt in December 1989. Obscure in its own time, the company's 386 Translator was the first plug-in board for Intel's newly released 80386 processor and the first mass-market computing device to offer consumers a means of using the 386 in July 1986.