Meaning of "multitasking" on iPhone, iPad, etc
in [UK Mac]
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From: Bruce Horrocks on 29 Jan 2010 19:31 On 28/01/2010 12:17, Woody wrote: > It is a daft omission in a lot of cases. Having a jailbroken iPhone, > which has multitasking and proswitcher which lets you switch between the > applications by pressing and holding the home button, which gives you a > view of all apps that you can select, it shows how slick it could be. > > It would be hard to go back from the multitasking to the singletasking > option. What impact does it have on the battery life? (I kinda assumed that the only reason Apple blocked multi-tasking was to eke out the battery a bit more.) -- Bruce Horrocks Surrey England (bruce at scorecrow dot com)
From: Bruce Horrocks on 29 Jan 2010 19:38 On 28/01/2010 12:43, 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.[1] It's possible, that the bits Apple added to the ARM core in their A4 chip are effectively single-tasking, perhaps because so much work has been off-loaded from software to silicon in the search for speed, that context switching becomes prohibitively expensive. [1] Okay, so back in SystemIII days it might have run on non-VM processors but back then malware didn't exist. -- Bruce Horrocks Surrey England (bruce at scorecrow dot com)
From: Ian McCall on 29 Jan 2010 20:04 On 2010-01-30 00:38:58 +0000, Bruce Horrocks <07.013(a)scorecrow.com> said: > Not necessarily. Unix is a multi-tasking OS but only on CPUs that > support it.[1] It's possible, that the bits Apple added to the ARM core > in their A4 chip are effectively single-tasking But not in their current off-the-shelf iPhone chip. Also, the fact the jailbroken machines multitask fine precludes there being any silicon-based restriction. Cheers, Ian
From: James Taylor on 30 Jan 2010 01:39 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 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. > [1] It's possible, that the bits Apple added to the ARM core > in their A4 chip are effectively single-tasking, ARM specialises in low latency interrupt handling, and large numbers of registers in separate banks for the various processor modes, all of which allows particularly efficient multitasking. As a RISC OS user for many years, and ARM assembly programmer, I should know. > 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. -- James Taylor
From: Woody on 30 Jan 2010 02:46
Bruce Horrocks <07.013(a)scorecrow.com> wrote: > On 28/01/2010 12:17, Woody wrote: > > It is a daft omission in a lot of cases. Having a jailbroken iPhone, > > which has multitasking and proswitcher which lets you switch between the > > applications by pressing and holding the home button, which gives you a > > view of all apps that you can select, it shows how slick it could be. > > > > It would be hard to go back from the multitasking to the singletasking > > option. > > What impact does it have on the battery life? (I kinda assumed that the > only reason Apple blocked multi-tasking was to eke out the battery a bit > more.) I haven't noticed any difference at all. However, I am not running 'heavy' applications in the background. -- Woody www.alienrat.com |