Why C for operating systems
in [General Programming]
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From: Bill Cunningham on 5 Dec 2009 18:59 One reason why I am so attracted to C and not just markup languages scripts and java is that C is for designing OS's. What exactley is it about C that makes it good to right operating systems? Bill
From: Beej Jorgensen on 5 Dec 2009 19:36 Bill Cunningham <nospam(a)nspam.invalid> wrote: > One reason why I am so attracted to C and not just markup languages >scripts and java is that C is for designing OS's. What exactley is it about >C that makes it good to right operating systems? http://en.wikipedia.org/wiki/C_(programming_language)#Uses http://answers.yahoo.com/question/index?qid=20071224070810AAUrfuP HTH, -Beej
From: Pascal J. Bourguignon on 6 Dec 2009 05:30 "Bill Cunningham" <nospam(a)nspam.invalid> writes: > One reason why I am so attracted to C and not just markup languages > scripts and java is that C is for designing OS's. What exactly is it about > C that makes it good to write operating systems? Nothing. Well, historical accident. Well, apart from the fact that it was developed to write unix. First, you should keep in mind that operating systems have been written in a lot of other programming languages, either assembler or high level programming languages. C is not the best system programming language, far from it. It just happened as an accident of history, that at a certain time in the end of the sixties and beginning of the seventies, appeared cheap and limited computers. Memory and processor speed was reduced on these "mini" computers, but it allowed them to be of a price more accessible. Therefore, while on the big and expensive computers, people had started to write operating systems in high level programming languages (eg. Multics in PL/1), on the PDP/10 Thompson, Richie and Kerningham had, there wasn't enough resources to run a high level programming language compiler. So they started to write unix in assembler. Of course, it is not very funny to write a lot of code in assembler, so they designed an assembler of slightly higher level, called B, and then made it evolve to C, as they got more powerful computers, such as the PDP/11. Nowadays, computers are millions of times more powerful (both in memory, processing speed and communication speed (Internet)), so that the requirement for a small OS is totally obsolete (for both workstations and embedded computers such as in GSM phones, even the processors in your phone is millions of times more powerful than the computers on which unix was developed!). Now the general belief is that C is good for OS because it has bit manipulation instructions, and allows you to access the hardware registers of the computer. But other programming languages have good bit manipulation primitives too, and the C language doesn't allow you actually to access hardware registers. If you read closely the C standard, you'll see that there's no standard way to access random memory addresses, or for example ix86 I/O port (using the INP and OUT instructions). It's even much less possible in C to access the status register, whose manipulation is essential when you write an operating system. For all these low level processor and hardware accesses, you have to use assembler, even when you're programing the rest in C, like in most other programming languages. Even something as fundamental as the system calls, just cannot be programmed in C, you have to write the syscalls in assembler, because they are not a normal "jump subroutine" instruction. Therefore C offers no advantage to other high level programming language for operating system programming. (Actually, C offers no advantage whatsoever, it's just an error. See http://www.netjeff.com/humor/item.cgi?file=c.hoax.txt ;-)) If you want to write an operating system, I'd advise Common Lisp, Scheme, Modula-3, Oberon, Haskell, or design your own high level programming language like BitC (http://www.bitc-lang.org/) in the CoyotOS project (http://www.coyotos.org). -- __Pascal Bourguignon__
From: bartc on 6 Dec 2009 05:59 "Pascal J. Bourguignon" <pjb(a)informatimago.com> wrote in message news:878wdgiedq.fsf(a)galatea.local... > "Bill Cunningham" <nospam(a)nspam.invalid> writes: > >> One reason why I am so attracted to C and not just markup languages >> scripts and java is that C is for designing OS's. What exactly is it >> about >> C that makes it good to write operating systems? > > Nothing. Well, historical accident. > Well, apart from the fact that it was developed to write unix. .... > Therefore, while on the big and expensive computers, people had > started to write operating systems in high level programming languages > (eg. Multics in PL/1), on the PDP/10 Thompson, Richie and Kerningham > had, there wasn't enough resources to run a high level programming > language compiler. I know little about this history, but I do know the PDP10 was rather more powerful than that, unless someone forgot to add some memory. I think it was a different PDP. > Nowadays, computers are millions of times more powerful (both in > memory, processing speed and communication speed (Internet)), so that > the requirement for a small OS is totally obsolete (for both > workstations and embedded computers such as in GSM phones, even the > processors in your phone is millions of times more powerful than the > computers on which unix was developed!). That might be true, but I remember having some trouble connecting my phone to a few hundred timesharing terminals, magtape units and lineprinter (in fact it has enough trouble just turning on, taking a couple of minutes to do so). > If you want to write an operating system, I'd advise Common Lisp, > Scheme, Modula-3, Oberon, Haskell, or design your own high level > programming language like BitC (http://www.bitc-lang.org/) "The BitC bootstrap compiler compiles to portable ANSI C code." Seems like you can't get away from C really. -- Bartc
From: Pascal J. Bourguignon on 6 Dec 2009 08:19
"bartc" <bartc(a)freeuk.com> writes: > "Pascal J. Bourguignon" <pjb(a)informatimago.com> wrote in message > news:878wdgiedq.fsf(a)galatea.local... >> "Bill Cunningham" <nospam(a)nspam.invalid> writes: >> >>> One reason why I am so attracted to C and not just markup languages >>> scripts and java is that C is for designing OS's. What exactly is >>> it about >>> C that makes it good to write operating systems? >> >> Nothing. Well, historical accident. >> Well, apart from the fact that it was developed to write unix. > ... >> Therefore, while on the big and expensive computers, people had >> started to write operating systems in high level programming languages >> (eg. Multics in PL/1), on the PDP/10 Thompson, Richie and Kerningham >> had, there wasn't enough resources to run a high level programming >> language compiler. > > I know little about this history, but I do know the PDP10 was rather > more powerful than that, unless someone forgot to add some memory. I > think it was a different PDP. Ah, right! It was a PDP-7. Sorry for the confusion. >> Nowadays, computers are millions of times more powerful (both in >> memory, processing speed and communication speed (Internet)), so that >> the requirement for a small OS is totally obsolete (for both >> workstations and embedded computers such as in GSM phones, even the >> processors in your phone is millions of times more powerful than the >> computers on which unix was developed!). > > That might be true, but I remember having some trouble connecting my > phone to a few hundred timesharing terminals, magtape units and > lineprinter (in fact it has enough trouble just turning on, taking a > couple of minutes to do so). It's a question of software, not of hardware. If your phone doesn't have wifi, you could use bluetooth at 140 KB/s to connect to a terminal dispatcher and implement a time-sharing system in its 512 MB of RAM and 400 MHz of processor to deal with user requests on thousands of terminals. These users, as long as they'd be cryogenized in the 60's would be bewildered by the power of that time sharing computer system, providing then each with more RAM than they had hard disk space, and more flash disk space (32 GB/1000 = 320 MB each) then they'd ever seen in their previous life. Of course, we don't do that because we could for a hundredth of the price of the terminals, dispatcher and software, give each of them one same phone or a sublaptop computer. Nonetheless, these computers are more powerful. >> If you want to write an operating system, I'd advise Common Lisp, >> Scheme, Modula-3, Oberon, Haskell, or design your own high level >> programming language like BitC (http://www.bitc-lang.org/) > > "The BitC bootstrap compiler compiles to portable ANSI C code." Seems > like you can't get away from C really. It's an implementation choice that is rather irrelevant. C is used for what it is: a portable assembler. -- __Pascal Bourguignon__ |