Talk:Computer multitasking.html



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not imply unix was always multitasking

Removed: "UNIX, designed as a "single user" operating system in the 1970s, included most of the multitasking capabilities of its multi-user cousin MULTIX, and is today used for both purposes." Bad example because it is mostly untrue. Unix was very briefly a single user system, but got both multi-user and multi-tasking features very early, and at about the same time.

Perhaps we could find a better example of multitasking being recognized as a useful feature even in a single user OS, such as a PC OS? Paragraph 8 ("Although the original purpose behind the design...") would be a good place for it. --D

change wording not imply ordering

"To remedy this situation, most time-sharing systems quickly evolved a more advanced approach known as [preemptive multitasking]?. "

In context, this reads like preemptive multitasking developed after cooperative multitasking. Preemptive multitasking was tried in the early 1960s, but it turned out to be a lot harder to do reliably than anyone expected. Remember that back then, people routinely made I/O calls from applications and grabbing control away from somebody who had just issued a read to a paper tape reader often didn't work out all that well. I'm pretty sure that cooperative multitasking was a kludge to make multitasking work better by making sure that programs were in a suspendable state when they gave up control.

I'm not sure, however, whether a change is needed or will be an improvement. - DJK

multitasking vs multiprogramming vs time sharing

It seems those three notions are intermixed here. A clarification is needed.

• Multitasking is a generic term allowing multiple tasks to be run, without regard to timing.

• Multiprogramming is the possibility for multiple programs to be ready, and waiting for the processor to be free. The initial purpose of this was to allow a second program to run while the first one waited for some I/O to complete. Multiprogramming does not require any cooperation between programs, as there were no interactive users anyway. If a program needed the CPU for a long time, it could use it.

• Time sharing is a method where all ready tasks are given a fair access to the CPU.

• It should be noted that, multi-tasking (aka time-sharing) is a type of multi-programming. A multi-programming system is not a type of multi-tasking system however.

• Multi-programming was put in place to keep the CPU busy, and not waiting on IO while it could be serving other processes.

The goal of multiprogramming is to minimize idle time for the processor, and that was the primary objective in the times the processor time was expensive.

reading from a tape

"(e.g. reading from a tape)" ?? Dated? In a modern computer would this be comparable to reading from a drive or waiting for a result from memory or an external device? - Omegatron 18:06, Oct 13, 2004 (UTC)

Merge from co-operative multitasking

weak disagree : I'd suggest that rather than merging, just add a "main article" link, as it could be argued that co-operative multitasking is a valid and reasonable article in it's own right. Guinness 11:31, 15 December 2005 (UTC)

agree : There's not a substantial amount of content in the separate article. I'd suggest that it be merged, and only split it if it later gets big enough. Currently it's mostly just redundant, and the little that's not is split across two articles. QuiTeVexat 05:59, 20 December 2005 (UTC)

observation: Preemption (computing) appears to describe the same thing also. I'm not familiar with the procedures around here, so I leave it to someone else to tag it. -- G. Gearloose (?!) 01:04, 5 February 2006 (UTC)

I am suggesting merging preemption into deadlock. The problem is, preemptive multitasking and preemption of resources aren't exactly the same thing, although they are related. Also, I'm not sure a full article can be written on just preemption. Perhaps a split is a better choice? MagiMaster 09:04, 10 July 2006 (UTC)

Can you explain what you mean by "preemption of resources"? --Chris Purcell 17:00, 10 July 2006 (UTC)

Merge from Co-operative multitasking and Preemption (computing)

The discussion at Talk:Deadlock seems to have generated a consensus against merging. The discussion here seems to have fizzled out without it being really clear if there is a consensus. Since both of the other articles are hardly longer than the sections here and don't look like growing (in my opinion) I would propose going ahead and merging those two articles into this article. This would also help remove the Merge backlog. Any objections? --Boson 21:52, 19 October 2006 (UTC)

I/O bound / CPU bound

Surely the terms "I/O bound" and "CPU bound" aren't states of processes, but properties of a program (or a portion thereof)? (Adjectvies where a

An I/O bound process may be time-limited by the speed of its I/O, but when it cannot continue until I/O occurs then it is "blocked", whether or not it's in a busy wait. If it's waiting for a signal rather than polling, then I'd call that "waiting".

Similarly a CPU bound process is "running" (or "on the CPU"), or if not, then it's "ready".

Multithreading

"Fibers are even more lightweight than threads, and somewhat easier to program with, although they tend to lose some or all of the benefits of threads on machines with multiple processors."

There is no reference to the advantages and disadvantages of multiple cores or processers in a multitreading system, and whether multiple cores benefit or hinder other types of multitasking. This is rather important with the current surge in development of multicore processors. I don't have enough knowledge of or experience with multicore systems to edit the article - can anyone else contribute to this? --[smiler 06:33, 16 February 2006 (UTC)

I also wonder exactly what this means, I added the citation needed template 222.225.196.13 03:06, 1 August 2007 (UTC)

how could a system be designed to allow a choice of operating systems to boot from

how could a system be designed to allow a choice of operating systems to boot from?

Typical multi-booting systems have a second-stage boot loader. On a PC, the second-stage boot loader sits in the MBR, and gets loaded by the BIOS.

216.23.105.20 22:41, 24 February 2007 (UTC)

Please specify

"One use for interrupts is to allow a simpler processor to simulate the dedicated I/O processors that it does not have."

I don't understand. A processor simpler than what (central or I/O?) is using interrupts to simulate the I/O processors?! —Preceding unsigned comment added by Doru001 (talk • contribs) 09:15, 16 April 2008 (UTC)

I know what this sentence was supposed to mean, but it is completely off-topic here. See channel I/O. Deleted it. Y Done --Kubanczyk (talk) 20:47, 2 July 2008 (UTC)

Alternating Multitasking

I was thinking should this topic contain topics on Alternating Multitasking, the term is not commonly used, but it describes a SIMD array processors, in which the processor tried do schedule 2 task at once by alternating sequence. So if there is 2 task, Work A and Work B. The sequences would be A, B, A, B, where task is A work, stop, work, stop. The concept is based on, overlapping the time between Task A stop and Time B work.

I know OCZ Enhanced Bandwidth and IBM Power Architecture threading uses this mechanism. Except IBM, does it a bit differently, because the instruction are very long that involves, prepare the query, fetch...etc. The time between preparition of thread is overlapped by implanting a XDR RAM. It is not really a true alternation method, but it achieve by the following

• Since it is slower at preparing threads (in Data cache), it implants a XDR RAM so it can (use that time to prepare for instruction cache and decoding) therefore the total wasted (or buffer) time is not wasted.

The only problem is that the speed that XDR RAM is not enough so it can only reach 1 petaFLOPS (or roughly tenfold) instead of at a more scalable multiple.

Usually when components are doing Alternation, it is best when one rate is faster than the order. --Ramu50 (talk) 01:45, 7 October 2008 (UTC)