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SSE2 is the first generation of SIMD (Single Instruction Multiple Data) extensions giving ability to process two double precious floating point numbers at once, and more abilities to previous Integer only extension (MMX).
So what does this have to do with Qt 5? Well, they are using SSE2 (and higher versions if detected) on their 64bit releases, which accelerates their QML stuff. However on 32bit builds, all kind of SSE optimizations are turned off (By default). So this is going to be a pure win for modern CPU owners, who are running a 32bit OS.
Regards to the SSE3, it's going to give them ability to process 4 single precious floating point numbers (stored in one SIMD register) horizontally which wasn't possible (directly) in previous generations. This might be slower or faster depending on the hardware.
yes sse2 adds instructions to process 2 double precision floats, while sse1 was mainly used for four 32bit floats
sse2 ports the mmx integer instructions to xmm registers (mmx registers are 64bit while xmm are 128)
sse2 also adds nontemporal stores for xmm registers (write directly to ram, bypassing cache)
this is going to be a loss for 32bit OS people running QT things on sse2 capable cpus
at least for default compiled QT
sse3's horizontal things and couple new instructions are useful for some algorithms (boasted that its for DSP and 3D)
it all depends on how you need to process data and i doubt QT will need them (idk)
why disable it on builds ?
cpu dispatching should be fine enough mechanism for one build to work good on all cpus
QT devs probably have their own reasons
Believe it or not, my old Pentium3 750MHz box (bundled with 256MB of memory and an ATI Radeon 7000) is not even capable of running a bare minimum install of Openbox with light weight set of GTK applications smoothly, don't even mention running LXDE, XFCE, etc. CPU usage goes %100 even when only trying to play music and whole system goes nearly unusable. Now you are hoping to run VLC and play HD videos too on these old farts?
The best use that I have found for that box is a headless (home) FTP server and download manager.
I haven't tested Linux 3.anything on a P-III yet, but I do have an old P-III/450MHZ box with Ubuntu Maverick (10.10) on it. If you use Audacious to play music, no sweat. I used a similar 500MHZ Athlon box as an audio playback server for years with little load on it. With Maverick, that box can play QVGA video with no issues, is just slightly slow for VGA/mpeg-4 video, cannot handle 360p/H264 video. On a Pentium 4 box I found a Quantal (Ubuntu 12.04) based Mint/MATE install to be essentially a match for Ubuntu Hardy on that same box for performance.
Make sure that update-manager or some other background process is not trying to run and hogging the CPU on anything this old! Open a terminal and run Top, look at what is running. Update managers and things like apt's xapian index are common culprits, you cannot use them on something this old. Same goes for Pulseaudio-older machines can't handle the overhead.
Some of the slower Coppermine or Tualitin-based Celerons used surprisingly little power at slower speeds and are thus better suited to minimally-demanding applications that they can handle than a Pentium 4, especialy a power-hogging Prescott chip. File servers, print servers, sound servers, you name it! No reason to spend $300 on an Atom box to do this, don't know if the difference between a 10W box and a 30W box can pay the environmental costs of producing a new computer from raw materials all the way back to the mine.
A tougher choice exists when setting up web computers and Pentium 4's are what's available. Strip down to OS a bit, use alternate versions of packages compiled for newer systems, do NOT use the new style desktop environments and they work-but there an Atom/Fusion box saves a lot more power if the machine will run for many hours a day. Hell to find graphics cards for AGP versions that can play H264 in hardware, cannot play 1080p video without them. Still, I see a LOT of these in use in my community, and many people never see a single 1080p video file due to bandwidth.
The Athlon 64 should probably be considered the "first modern processor" that modern distros need to be able to support. I've got one with a Radeon HD4350, Ubuntu 13.10/Cinnamon on it, and it can play a 1080p H264 video using VDPAU on the open driver while running the Cinnamon desktop. It can do anything my Bulldozer box can do except edit HD video or play demanding games. Yes, it supports SSE2. By comparison, Athlon XP does not, and Atlhlon Thunderbird lacks SSE entirely.
You realise that there are distributions like Gentoo or ones dedicated to old hardware support? It's a default that can easily be changed.
Yes, I realize that. As a Slackware user I am used to compile software from source. My statement was merely directed at such nonsense like
Originally posted by Alliancemd
People with such old processors don't use new software
Originally posted by darkcoder
If you have an old 2000-2003 computer you should either stop using new software and go back to Win 98/Linux 2.x based kernel distro, or get new hardware... plain and simple.
Yes, while Gentoo well tuned can do miracles (I used it for a couple of years), some people try to use very old computers with the latest software.
Having an old computer does not at all mean that you have to use old and unsupported software, it only means that you have to choose the software you use with regards to resource usage, which doesn't disqualify using Qt based software.
Where the hell did you get that info from? So people with older CPUs don't use Razor-Qt or now LXDE-Qt? Also they don't use VLC or other Qt based software?
You realize that more software than just KDE is using Qt?
IWith all the advancements in low power CPU and APU systems a bottom of the line Atom or Brazos based system will blow your decade old CPU out of the water and use fraction of the power to do so.
It's time to let go of pre 64-bit hardware. Just because it still runs doesn't mean it's still worth running. A Model T Ford may still work, but you wouldn't choose one as your daily driver.
Any specialized low performance requirement you have for old hardware can probably be done on an ARM chip for even less power consumption with the same or better performance over the decade old x86 hardware.