Meaning of "multitasking" on iPhone, iPad, etc
in [UK Mac]
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From: Woody on 1 Feb 2010 10:36 Jack Campin - bogus address <bogus(a)purr.demon.co.uk> wrote: > > The iPhone has a hardware button below the screen, which you press whenever > > an application is running, in order to get back to the 'home' screen, i.e. > > the screen with all the pretty little icons. > > > > If you're running an application, say you're listening to a foreign radio > > station, and you want to check your e-mail, the radio application will exit > > if you press the hardware button. That is, the radio will stop. You then > > have to launch it again and do whatever it requires, to get the radio back. > > CHECK your email? You don't get a "you have mail" notification? Yes, but it doesn't tell you what is in the mail unless you go and look -- Woody
From: Bruce Horrocks on 1 Feb 2010 11:31 On 31/01/2010 13:14, Chris Ridd wrote: > On 2010-01-31 11:36:56 +0000, Richard Tobin said: > >> In article <7sk0prF75pU1(a)mid.individual.net>, >> Bruce Horrocks <07.013(a)scorecrow.com> wrote: >> >>> Early hardware support for multi-tasking didn't support virtual machines >>> in the hardware so one process could reasonably easily see another's >>> address space. >> >> The term "virtual machine" already has two common uses. Using it to refer >> to protected address spaces is just confusing. > > I expect Bruce meant virtual memory. The meaning and, particularly, the scope of the term 'virtual machine' has changed considerably over time. My usage of it was (IMHO) correct for the vintage of machine I was referring to. However, I accept that it is still confusing. ;-) -- Bruce Horrocks Surrey England (bruce at scorecrow dot com)
From: Rowland McDonnell on 1 Feb 2010 12:43 Ian McCall <ian(a)eruvia.org> wrote: > Chris Ridd <chrisridd(a)mac.com> said: > > > Oh could be, but that's just the deeply crummy way that Intel revved > > the x86 architecture isn't it? Better designed processors didn't need > > to work this way. > > True, but I have a small smidgin of sympathy. Intel hit a problem > no-one else really hit at that time, how to keep backwards > compatibility at the hardware level at a time when things were still > being programmed in assembly and not high-level languages. 68000 line > managed it, x86 line managed it, most others didn't (rip MOS). I thought one of the points of the 68000 was that it *wasn't* backwards compatible with the 6800 series. And one of the big mistakes Intel made was in providing that backwards compatibility, which just wasn't sane at the jump to 16 bit. I don't see any sign that the ability to run 8 bit code helped the take-up of the IBM PC, for example. And from what I recall, the reason the 8085 (or 8088?) was used ratehr than the superior 68000 was that Intel could deliver in quantity when Motorola couldn't. Nothing to do with technical anything, purely to do with availability - that's why the x86 line took off. Or so I've long understood: Intel could make 8086/85/88s in bulk at the time; Moto was still trying to sort out the 68000 manufacturing process. Rowland. -- Remove the animal for email address: rowland.mcdonnell(a)dog.physics.org Sorry - the spam got to me http://www.mag-uk.org http://www.bmf.co.uk UK biker? Join MAG and the BMF and stop the Eurocrats banning biking
From: Rowland McDonnell on 1 Feb 2010 12:54 Bruce Horrocks <07.013(a)scorecrow.com> wrote: > On 30/01/2010 06:39, James Taylor wrote: > > Bruce Horrocks wrote: > > > >> James Taylor wrote: > >> > >>> So, despite the fact that the iPhone OS *is* a multitasking OS, the GUI > >>> actively quits applications you are using as you switch. Apple must have > >>> done *extra* work to include that feature. > >> > >> Not necessarily. Unix is a multi-tasking OS but only on CPUs that > >> support it. > > > > Eh? No modern processor lacks the ability to run a multitasking OS. > > Indeed it is hard to imagine any processor architecture in the history > > of computing where multitasking is impossible. Unix has been around for > > a long time and I've never heard of it not multitasking. Please explain. > > > >> [1] Okay, so back in SystemIII days it might have run on non-VM > >> processors > > I apologise for pulling you up on your statement. You are correct for > all practical purposes. If you had claimed that all non-electric cars > use internal combustion engines then my response was the equivalent to > pointing out that there are still a few steam powered cars lurking > around in museums. Technically correct but mostly confusing the argument. Six stroke engines are appearing; combined internal combustion and steam expansion. Modern. Bang up to date. Two current patented designs being worked on. There are also some modern steam and compressed air powered cars under development and in service - it's an avenue that's being explored again. There are even a few jet and rocket powered cars around the place. There's at least one jet powered trike in the UK which was road legal in its first year of life - MOT, tax, insurance, the lot. Just drive it using the Rover V8, not the Rover jet that's also attached until you get to private land, and *then* you can start showing off. > > What exactly is a non-VM processor? Are you talking about the > > virtualization support of the latest 64 bit Intel (VT-x) and AMD (AMD-V) > > processors, or the virtual memory management employed by operating > > systems? The former is not required for multitasking, and the latter is > > not a feature of the CPU anyway. Also virtual memory management and is > > an independent concept to multitasking so you can have either virtual > > memory, or multitasking, or both. Neither feature is required for the > > other to work. They are entirely orthogonal. > > > >> but back then malware didn't exist. > > > > What has malware got to do with it? You can run malware on any > > processor, and on any OS, regardless of whether it multitasks. > > Early hardware support for multi-tasking didn't support virtual machines > in the hardware so one process could reasonably easily see another's > address space. Well, yes, but that one was dealt with in the 1960s, before I was born, wasn't it? [snip] > >> perhaps because so much work has been off-loaded from software to > >> silicon in the search for speed, that context switching becomes > >> prohibitively expensive. > > > > Each new generation of ARM architecture gets better and faster at this > > kind of thing, not worse. I cannot imagine where you get your strange > > ideas, and I think you should explain yourself. > > The ARM core does indeed get better - but if you look closely I said the > 'bits Apple added to the ARM core'. Nothing at all. >Apple's A4 chip almost certainly > doesn't change the ARM core. Scrap `almost' - it'd be mad to do so. > But it can add other functionality. Yeah, but you wanna look at the design tools that ARM supplies, the kit of parts ARM supplies to play with using those design tools, and you wanna look at just how damned clever those PA Semi guys and gals are. > Trivially, for example, HP recently had Atmel add 7-segment display > support to one of their low-power ARMs. That's the sort of thing that was being done in the 1980s. > So what additions might Apple want to make and how might they impact > multi-tasking? Well, the multi-touch screen is one obvious candidate for > h/w support. Yeah, as was the original Mac mouse, which was all done in software, not with the fancy hardware everyone *KNEW* was necessary to avoid mouse lag etc. Apple's history is `do as much in software as possible, integrate it all very tightly, because that's cheaper than hardware. But do it in hardware when needed.' > Another might be replacing sections of core Cocoa library > routines with dedicated silicon. Flash RAM might hold things like that. Apple gave up on putting that sort of thing in ROM for Macs years and years ago, didn't it? There was a reason for that. I can't see any reason to do what you suggest. >It doesn't really matter what the > change is, my point was to suggest that Apple may have optimised so much > that multi-tasking was compromised. I'd be willing to bet a very large sum of money that the A4 doesn't compromise multi-tasking in any way, and that the hardware is not as you suggest it might be. >It's not that multi-tasking has been > made impossible, just that the speed benefits are lost if it is enabled. > Hence my comment about context switch times. I'd be willing to bet that it's got fast context switching. Just look at the way things are going with the whole LLVM and GCD and - oh, all the fancy new tech that Apple's got hold of now and is using to develop all its software AFAIK. > This, of course, and I freely admit, is pure speculation. In a few years > we may find out from Apple themselves as to why the single-tasking > limitation exists. It's a user experience decision, not one forced on the user by under-the-bonnet restrictions. Anyone want to take the bet? Rowland. -- Remove the animal for email address: rowland.mcdonnell(a)dog.physics.org Sorry - the spam got to me http://www.mag-uk.org http://www.bmf.co.uk UK biker? Join MAG and the BMF and stop the Eurocrats banning biking
From: D.M Prosciutto on 1 Feb 2010 13:58
On Mon, 1 Feb 2010 17:54:01 +0000, Rowland McDonnell wrote: > There are also some modern steam and compressed air powered cars under > development and in service - it's an avenue that's being explored again. Is your head on right? Where do you think compressed air comes from? You have to expend energy to compress it, along with additional losses when you expand it. Where do you think steam comes from? You have to expend large quantities of energy to produce it. You are a complete engineering nitwit if you think there is anything useful in those stupid ideas. -- "And if the above text makes me sound snooty and convinced of my own superiority, it's because I am convinced of my moral superiority over many people on this matter." Rowland McDonnelI - Now Morally Superior - Aug. 7, 2008 |