# HG changeset patch # User Rob Landley # Date 1367818197 18000 # Node ID e50c2b9588b8d5e94afa90bf06a2b32868512b56 # Parent e8d846fb56eb6642c848978cf7de562c690b4ff5 Fluff out the architectures page. diff -r e8d846fb56eb -r e50c2b9588b8 www/architectures.html --- a/www/architectures.html Tue Apr 30 00:27:52 2013 -0500 +++ b/www/architectures.html Mon May 06 00:29:57 2013 -0500 @@ -2,72 +2,31 @@ Target architectures -http://www.fool.com/portfolios/rulemaker/2000/rulemaker000224.htm + +

Thumbnail oversimplification of processors:

-Before Linux - -

In the 1950's and 60's -mainframe -and minicomputer processors took up an entire circuit board. Unix -started on these kind of systems, few of them remain in use today.

- -

In 1969 an engineer -at Intel invented the first microprocessor, the Intel 4004, by being the -first to squeeze all the functions of a CPU onto a single silicon "chip". -As transistor -budgets -increased -they upgraded the 4004's design into the 8008 and then the 8080, the chip -inside coin-operated Space Invaders machines and the Mits Altair. The Altair -was widely cloned to form the first family of microcomputers, which contained -(and were named after) the S-100 bus, programed in Basic from -a startup called Micro-soft, and ran an OS called -CP/M -from a startup called Digital Research.

+

ARM

@@ -175,7 +134,17 @@

Motorola 68000

-

Very popular in the 80's. +

Very popular in the 80's, the first widely used 32-bit processor. +It was in the original Apple Macintosh, the first Sun workstations, the +Commodore Amiga, the Atari 800, and so on.

+ +

Still trying to get QEMU to support it, the Aranym Atari emulator has +run an Aboriginal M68k chroot but requires a different kernel config. +In theory the q800 branch of git://gitorious.org/qemu-m68k/qemu-m68k is +working on support for the last m68k macintosh model (supporting 256 megs +of ram), but in practice it doesn't boot Linux yet.

+ +

Coldfire is a nommu variant used in early handhelds.

Mips

@@ -214,9 +183,6 @@

The company's website talks about their customers.

- -

-

PowerPC

Apple's original Macintosh computers used Motorola 68000 processors. @@ -240,11 +206,295 @@ and some supercomputers. These days the power architecture is maintained by a consortium. - and + +

SuperH

+ +

Japan's first major homegrown 32-bit processor architecture was widely +used in the automotive industry, and wound up in the dreamcast gaming +console. Often called "sh4", because although there were sh versions 1 through +3 they didn't really make it out of Japan.

+ +

Although sh4 is reasonably well supported by QEMU, Hitachi spun this +processor design off into a seprate company called Renesas, which ranges +from "confused" to "actively hostile" at the idea that anyone who isn't already +a paying customer might be interested in this processor.

+ +

Sparc

+ +

Created by Sun Microsystems as a replacement for the m68k, and mostly +used in-house by them until they went out of business. (Fujitsu made some +supercomputers with it, during the same period Alpha and iTanic were used in +that space.) Oracle bought Sun's corpse, but according to James Gosling +(creator of the Java programming language), they were more interested in +the lawsuit potential than the technology.

+ +

x86

+ +

The standard PC architecture, in 32-bit and 64-bit flavors.

+ +

The reason the x86 directory in Linux is newer than some other architectures +is the 32-bit and 64-bit directories were merged together, and the date of +the oldest commit in the directory is the merge. In reality, i386 was the +original Linux architecture back in 1991.

+ +
+ + +

What processors are supported by Linux, and when was support added +for each one?

+ +

We can actually beat this information out of the linux-fullhist git repository, by doing:

+

+cd arch && for i in *; do echo -en "$i\t" && git log $i | sed -n 's/^Date:[ \t]*//p' | tail -n 1 | awk '{print $2" "$3" "$5}'; done +

+ +

Removing "Kconfig" and "um" (user mode linux, not a processor type), +as of the 3.9 kernel this gives us:

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
alphaNov 27 1994
sparcDec 4 1994
mipsJan 12 1995
m68kMar 7 1996
armJan 20 1998
shJun 30 1999
ia64Jan 4 2000
s390Mar 10 2000
pariscOct 3 2000
crisJan 30 2001
umSep 11 2002
h8300Apr 17 2003
m32rSep 16 2004
frvJan 4 2005
xtensaJun 23 2005
powerpcSep 19 2005
avr32Sep 25 2006
blackfinMay 6 2007
x86Oct 11 2007
mn10300Feb 8 2008
microblazeMar 27 2009
scoreJun 12 2009
tileMay 28 2010
unicore32Feb 26 2011
openriscJun 4 2011
c6xOct 4 2011
hexagonOct 31 2011
arm64Mar 5 2012
metagDec 5 2012
arcJan 18 2013
+ +

This doesn't quite tell the full story: the x86 and powerpc directories +were created by merging together 32 bit and 64 bit versions of the same +architectures: the i386 and x86_64 directories for x86, and the ppc and ppc64 +directories for powerpc. (A similar merge of arm and arm64 is expected when +ARMv8 support stabilizes.)

+ +

The resulting dates are when the merge happened, +the corresponding architectures were added much earlier.

+ + +

Where did all these processors come from?

+ +Before Linux + +

In the 1950's and 60's +mainframe +and minicomputer processors took up an entire circuit board. Unix +started on these kind of systems, few of them remain in use today.

+ +

In 1969 an engineer +at Intel invented the first microprocessor, the Intel 4004, by being the +first to squeeze all the functions of a CPU onto a single silicon "chip". +As transistor +budgets +increased +they upgraded the 4004's design into the 8008 and then the 8080, the chip +inside coin-operated Space Invaders machines and the Mits Altair. The Altair +was widely cloned to form the first family of microcomputers, which contained +(and were named after) the S-100 bus, programed in Basic from +a startup called Micro-soft, and ran an OS called +CP/M +from a startup called Digital Research.

+ +

One of the +Intel engineers left to form his own company that made an 8080 +clone called the Z80. But the main alternative to the 8080 was from +some ex-motorola engineers who left form MOStek, the company +that did the (much cheaper) 6502 processor, with its own instruction +set. Motorola sued the escaped engineers for being better at it than they were, +and in the end the engineers went back to Motorola and +commodore bought the rest of the company to use these processors in the Vic 20 +(the first computer to sell a million units) and its successor the Commodore +64 (even more popular). The 6502 also wound up running the Apple I and Apple II, +and the first big home game console (the Atari 2600).

+ +

The march of Moore's Law quickly drove the microcomputer world to +move beyond 8 bit processors. Moore's Law says that memory size doubles +every 18 months, which quickly became a self-fulfulling prophecy hardware +manufacturers used to manage inventory and schedule product releases.

+ +

The first widely cloned microcomputer (the MITS Altair) was introduced in +1975, and by the middle of the year established a range of 1-4 kilobytes of +memory installed in altair compatible systems. (The original Altairs +had only 256 bytes memory, but that wasn't enough and 1k expansion boards +immediately became standard equipment. The first version of its standard +de-facto standard programming language, Micro-soft basic, required 7k of +memory to run but that was too expensive so they trimmed it down to run in +4k.) From then on Moore's Law turned the old high end into the new low end +every 3 years. (In 1978: 4-16k. In 1981, 16-64k.)

+ +

These early microcomputers were called 8-bit machines because they had +8-bit registers, storing values from 0 to 255. But they used pairs of registers +to access memory, providing 16 bits (64k) of address space. That was enough for +four 18-month Moore's Law doublings before the high end of the microcomputer +address range hit the 64k address space limit in mid-1981.

+ +

The result was a switch to 16-bit systems. IBM introduced its PC in +August 1981, based on Intel's 8086 processor (actually a variant called +the 8088 that ran the same software but fit in cheaper 8-bit motherboards +and took twice as many clock cycles to do anything). True to form, it +offered anywhere from 16k to 64k of memory preinstalled.

+ +

The main competitor to the 8086 was Motorola's 32-bit 68000 line of +processors, used in just about everything except the PC (Macintosh, Amiga, +Sun workstations...) Just as the Intel's 8086 was a sequel to the 8080, +the Motorola's 68k was a sequel to the 6502.

+ +

Motorola skipped 16 bit registers and jumped straight to 32 bits, but back +when 64k was as much memory as most high-end users could afford (costing +hundreds of dollars) this provided no immediate market advantage. The 68k +powered Apple's Macintosh (and several incompatible designs such as Commodore's +Amiga and Sun's original unix workstations). But Apple successfully defended +its hardware design in court, while IBM lost its court case +against Compaq, spawning an army of clones that quickly marginalized the +proprietary hardware designs and rendered the PC the standard computer.

+ +

The 8086 also used pairs of registers to access memory, but it overlapped +their address ranges so instead of 16+16=32 bits of address space, each +"segment" started only 16 bits from the previous one (with a 64k offset that +mostly redundantly accessed the same memory as other segments), providing +16+4=20 bits of address space, for 1 megabyte. (The 640k limit of DOS was +because the top third of the address range was reserved for I/O memory, +starting with the video card's frame buffer.)

+ +

The continuing advance of Moore's Law meant high-end PCs would collide +with the 1 megabyte limit in 1987. To prepare for this, Intel introduced its +own 32-bit processor, the 80386, in 1985. Unfortunately IBM had bought the +entire first year's production run of Intel's previous processor (the 80286) +to keep it out of the hands of the PC cloners, and Moore's Law quickly left +IBM with a giant unsold pile of slow expensive processors. This delayed +its introduction of new 32-bit PCs until the original cloner introduced +the "Compaq Deskpro 386" and the rest of the clones followed that, leaving +IBM's PCs in obscurity.

+ +32 bits and RISC + +

In the 1980's and 90's, a +new +technology called RISC led to a gold rush +of processors hoping to take market share away from Intel. These risc designs +came from three sources: start-up companies producing new RISC processors, +surviving mainframe and minicomputer vendors redesigning their big iron to use +microprocessors, and m68k users giving up on that design once Intel's move +to 32 bits removed the only argument in its favor. (If m68k had lost out to +16 bit x86, clearly it was even less interesting after the 386 came out.)

+ +

RISC designs ("Reduced Instruction Set Computers") simplified processor +instruction sets down to fixed-length instructions that only took one clock +cycle. This led to more verbose machine code which took up more memory, but +also meant that since you didn't have to execute the previous instruction +to figure out where the next one started (because they're all the same size), +processors could contain a second "execution core" looking over the shoulder +of the first core to potentially execute the next instruction in the same +clock cycle (if it didn't use the same registers, memory locations, or depend +on processor flags set by the previous instruction). Once compilers +advanced to produce instructions in non-interfering pairs, RISC processors +added a third core to potentially execute a third instruction in the same +clock cycle (if that one didn't interfere with the first two).

+ +

Several processor manufacturers were convinced that RISC designs were +superior to the older designs (which they called "CISC", for Complex +Instruction Set Computers). The commodity PC had taken over the market, +running a large installed base of CISC software, but the cloners were +sure that during the 16 to 32 bit transition they could capture the market +when everyone had to throw out their old software anyway.

+ +

MIPS was one early RISC startup, created and commercialized +by some university professors based on early RISC research. The ARM design +came from a tiny start-up in the UK which made the Acorn Risc Machine and +got a contract with the British Broadcasting Service to sell it as the "BBC +Micro" in conjunction with BBC educational programming.

+ +

At the other end of things, IBM engineers produced the Power minicomputer +architecture, Hewlett Packard developed PA-RISC, Hitachi developed the +SuperH (more commonly known as sh4), and Digital Equipment +Corporation migrated its VAX minicomputers to their new Alpha processor +(the first 64 bit processor).

+ +

Sun Microsystems develop the Sparc processor to replace m68k, but the +official successor to m68k came from a partnership between Apple, Motorola, +and IBM, redesigning IBM's Power processor to produce PowerPC. (Apple's +macintosh redesign brought its m68k vendor Motorola together with IBM, +which at the time had the world's leading microchip manufacturing facilities. +The 90's were a great decade for IBM's microprocessor manufacturing arm: first +to replace microchips' traditional aluminum wiring with copper, first to layer +"silicon on insulator" to improve power efficiency, first gigahertz +processor...)

+ +

When the PC market smoothly transitioned to the 80386, +the RISC proponents were sure that better technology would eventually +prevail over market forces. The 386 was an extension of the 8086 which was +an extension of the 8080 which was an extension of the 8008. And the 386 wasn't +just similar to previous designs to ease porting, it actually implemented a +compatability mode to fully emulate the previous chip and run its software +unmodified! Surely this long chain of backwards compatability that had +accumulated customers for 20 years until it snowballed into market dominance +had to collapse from accumulated complexity at some point?

+ +

Next Intel came out with the 486, which introduced +CPU cache, allowing for "clock doubling" and "clock tripling" to run the +processor faster than the rest of the motherboard and execute loops of code +in cache while the slower main memory delivered the next part of the program +and stored the cached results of earlier computations. But the RISC proponents +saw this as merely buying time, sure that RISC would still win the day.

+ +

Then Intel introduced the Pentium, which translated CISC instructions +into RISC internally. It could run as fast as RISC designs (executing two +instructions per clock cycle) while remaining compatible with existing +software.

+ +Mobile processors + +

Intel did hit a bit of a wall at 1 gigahertz, and produced +a horrible RISC-like design (itanium) as its planned 64 bit transition, +but AMD filled the gap with other x86-compatible designs and a sane +64 bit extension of the x86 architecture (x86-64), and Intel's customers forced +it to adopt AMD's 64-bit design.

+ +

Intel and AMD competed on two metrics: absolute performance, and the +price to performance ratio. They tried to produce the fastest chips, and +the fastest chip for the money.

+ +

But in the late 90's laptop systems became a viable PC option, and +in 2005 laptops outsold desktops. These systems are battery powered, and +care about another metric: power consumption to performance ratio. The +best performance for the battery life. In 2000 a startup called Transmeta +(most widely known for employing Linus Torvalds in his first job out of +college) proved that a processor consuming just 1 watt could provide +reasonable performance. (Meanwhile Intel's itanium and Pentium 4 processors +consumed around 90 watts, enough power to fry an egg on the heat sink.)

+ +

The processor with the best power consumption to performance ratio was +ARM, which came to dominate the cell phone and handheld systems. When those +coverged into smartphones, arm retained its dominant position.

+ +

Recently introduced processor designs attempted to compete with Arm, not +Intel. Coldfire was a stripped down version of m68k, and new designs include +blackfin, hexagon, tile, and so on. So far, these are doing as well against +arm as the RISC gold rush did against x86.

-

Super Hitachi

-

Sparc

-

x86

+