Some elementary concepts about computers.
 

Hi:

I happen to have a new machine and a new OS and before going ahead I'd like to have some concept clear:

(a) In the 1990s there was a desktop computer called IBM PC, and a lot of machines designated by thw words IBM PC compatible, which were just clones of the former. Do these words designate anything that has been released, say, in the last five years?

(b) What are, at present, the main categories of desktop computers? I guess a division could be made according to the processor (CPU) brand the machine is using. What would then the categories be (according to this criterium, I mean). Or what is the most useful criterium to make a division?

Well, no more questions for the time being.

The IBM PC was in the 80s, not the 90's. It used a processor with 8-bit buses, but a 16 bit instruction set and 20-bit physical memory addresses.

That architecture (now generally called "x86") has evolved in many stages, each time keeping legacy support for all previous stages. Most desktop computers today are x86_64. Those CPUs have full support for booting up in a mode compatible with the 16-bit instruction set of PCs from the 80s. The motherboards, BIOSs and peripherals remained fully "PC compatible" for a long time. I'm not sure about the status now. There is quite a lot still done to retain "PC compatible" behavior at boot time in new computers, but I'm not sure whether that is enough to really mean what "PC compatible" meant in the 90s (when later generations of x86 existed, but BIOSs and motherboards etc. were strictly PC compatible at boot time).

Some earlier x86 modes of operation were supported by each new x86 generation at full new performance as sub modes of the new architecture. That means programs written for some older x86 architectures run directly in the new CPU along with new architecture programs. 32-bit x86 supported at least two different generations of 16-bit x86 programs that way.

Current 64-bit CPUs are fully compatible with 32-bit OS's that can run 16-bit programs mixed in with 32-bit programs. But those CPUs cannot switch from 64-bit mode all the way down to 16-bit mode without rebooting. You need a 64-bit OS to run 64-bit programs. Once you are running a 64-bit OS, individual programs directly running on the CPU can be 32-bit, but not 16-bit. Software has been written to cover up that limit. 32-bit or 64-bit software (running under a 64-bit OS) can simulate the old 16-bit architecture, so a 16-bit program runs far slower than it might if you had booted the same 64-bit CPU into a 32-bit or 16-bit OS, but that is still far faster than that program could have run on any 16-bit CPU.


Such a large fraction of current desktop computer CPUs are x86_64 architecture that I'm not convinced you really want to consider anything else.

Your post gives ample response to my questions. Now, there was not, once upon a time, a desktop based on the Motorola 68000 processor? Was't the manufacturer Apple?

Greetings,

Well, to start with:

a.) Back when there really *was* the IBM PC (starting about mid-80s), "PC" supposedly stood for "Personal Computer" (unless you asked my mother at that time, where she would tell you it stood for "Profusely Corded" ;) hehe), and at the time, was considered more of a marketing gimmick since there were other "personal" (READ: "micro-") computers available and IBM was also making mini-computers to mainframes at that time. Overall, I believe that using the expression "PC" is still valid to use when referring to a desktop or laptop system nowadays.

b.) Well, you *could* run the usual dividing line of Intel vs. AMD when looking for ways of breaking down current offerings of desktops, but I don't think that really tells you much about what is going on with the system or what it can do. I think it is more effective to break them down by purpose: Clerical, General, Multimedia and Gaming.

1. Clerical - For office use, doesn't need multimedia, and generally just enough RAM to run a spreadsheet or a large word processor document.
2. General - Lightweight use, average home use. Reading emails, watch a couple vids from the internet, listen to music, etc.
3. Multimedia - Watching, editing and/or creating movies/music, Detailed graphics manipulation, desktop publishing
4. Gaming - High-end graphics, high speed processing, top-end 2-way sound for chatting real-time with the other folks you are playing with/against in the latest FPS or MMO game.

HTH. Let us know.

Yes... the PowerPC line of systems that were mainly Apple.

But, that's not all... Back in the early days, you also had systems being built off of the Zilog Z80 processor, but I'm not sure that they would classify as "desktop" computers. I think that would depend on whether or not you considered the Timex/Sinclair offerings to be a real "desktop" computers... I like to think of them as the first attempt at a 'palmtop' since they could sit in the palm of your hand. ;-p hehe

HTH.

Many brands of desktop computer were based on the Motorola 68000 processor, but I would guess Apple sold more 68000 based desktop computers than the rest of those brands combined (still a small amount compared to X86 desktops sold at the same time)

Apple later switched to the PowerPC family of CPUs, then in 2006 switched again, this time to X86_64.

There are current desktop computers that are not any version of X86. But I don't know any details about those. Non X86 consumer computers are much more likely to be tablets than desktop.

So AMD is also x86 or x86-64 architecture in spite of not being Intel? Of the four categories defined by you, where would a programmer feel comfortable without expending too much? Again I guess it'll depend on the kink of programs he writes. I knew machines based on Z80 and even bought one of those processors to see if I could make it work by myself. But I had to fall back on a columnist from the Byte magazine.

Well ... I'm being offered a machine built around an Intel G620 processor, which somewhere I learn is intended for use in entry level desktops (euphemism for low cost). At least I shall still be within Intel, though, as johnsfine seems to imply, there would be little difference if it were AMD. I think by now I have a couple of elementary concepts well defined. Thanks a lot. And thanks to johnsfine too.

AMD invented X86-64. Intel copied it from AMD.

Prior to that, AMD and Intel both made 32-bit X86 CPUs (AMD had various cross licensing agreements to use an architecture Intel invented).

Intel invented IA64 as a successor to X86. But it did not do well in the market, partially because it didn't provide a compatible enough transition from 32-bit X86. I think IA64 might still be one of the CPU architectures in current use. But most Intel 64-bit CPUs are X86-64, not IA64 (all Intel CPUs in ordinary desktop systems are X86-64, not IA64)

I don't have terribly current info on offerings from either Intel or AMD. From a programmer point of view or software compatibility point of view, X86-64 is the same regardless of AMD vs. Intel. The differences are price performance.

Over most of the time that they have both had X86-64 CPUs, AMD has had slightly better price performance at the low end and has had much better cross CPU communication at the super high end (hundreds or thousands of moderate speed cores coordinating to solve massive problems) while Intel has been far ahead in the ordinary "high end" (a small number of individually very fast cores working independently in one desktop size system). Since most software isn't very well multi-threaded, a small number of very fast cores is the best performance you can get for most problems. Then it is a question of whether that is worth the extra dollars compared to a small number of somewhat slower cores.

Lots of online info I see, claims AMD no longer has a price performance advantage at the low end. My own knowledge is not current enough to give an informed opinion on that. At that level, the price performance of the rest of the system makes a bigger difference than the AMD/Intel choice of CPU.

Thanks a lot for all this interesting and useful information. Regards.

The desktop i'm being offered is well into the low end, I think. They are 1750 argentine pesos = some u$s390 at the current change (here my English is highly deficient), but nontheless its very difficult to make money comparisons. The seller is one of those guys who build the computer for you on request, much more cheap than buying at a computer shop where they sell it already built, chassis and all that is inside.

But the price surprises me, for I think the components are good (I may be wrong) and this in a moment where little or nothing enters my country and the little that entries is very low quality. These are not my words but tthose of people who I trust. To say the components seem of not bad quality I am based on this list which the seller passed me:

Motherboard Gigabyte H61 (this brand I do not know it)
CPU Intel G620
HDD 500GB SATA Seagate
DDR3 4GB 1333MHz Kingston

The DVD I intend to buy it by myself. Now, Seagate and Kingston are known brands. Seagate specially I think is a good brand. Of course, within a given brand, there will be models of every quality level. But the price seems extremely low to me and can't understand why.

You can still find on the net old TV programmes such as The Computer Chronicles. There is an episode on Unix.

In the US, NewEgg sells four different models of Gigabyte H61 motherboard, for prices from $55 through $80 (the differences between the four were not very clear even in the comparison chart).

NewEgg sells the G620 CPU for $64
Typical Seagate 500GB hard drives at NewEgg are $70
Typical Kingston DDR3 4GB 1333 is $22

With a case and a power supply and assembly, someone could make a decent margin putting that system together from mail order parts at that price in the US. But I don't know how much extra it costs to get the same parts there.

Since you didn't mention a display, I assume one is not included?

No, a physical monitor or display is not included in the budget presented to me by the seller but it does include an LG DVD burner, the model he did not specify. From what some people with a similar job, but highly dependable people tell me, prices must be high due to government import restrictions.

It's quite a pity I have consulted LQ after just having advanced half the payment but, this man perhaps places large orders in this way getting lower costs. I mean, it is possible I would expend more money by mail ordering the parts and assembling them myself.

Moderator Response
 

Moved: This thread is more suitable in <General> and has been moved accordingly to help your thread/question get the exposure it deserves.

a). Thanks for making me feel ancient.
b). The divisions by architecture or expected use make sense to me, but I'm surprised nobody mentioned OS. I don't know that it's any more appropriate than architecture, but OS is certainly a clear dividing point.

Nowadays the OS is not that important anymore. If a user runs Firefox, Vlc and Libreoffice as main applications, maybe an additional mail client like Thunderbird or Claws Mail, just to get his/her stuff done, the underlying OS is not important at all, anything will work.

You asked about 'divisions' of computers...

I would say that the CPU manufacturer is a 'division', being only 2, for the most part; AMD, and Intel.

And I think AMD is less expensive, most factors / specifications being equal.

Yes and, hence, (almost) everything happens as if there is only one class, given both employ, at present, the x86(-64) architecture. This would have been a relief for me, in the case I had chosen AMD because, once in a while, I would like to play directly with the instruction set instructions themselves. And now that I know one of the most basic things within my computer, I'm ready to post about hard disks and the booting process on which, I know, there is plenty of literature for beginners like me. Which I'll do in this thread or most probable in a new thread. Thanks everyone for their kind assistance.

But the above applies to divisions of architecture and processor as well.

The use categories that ShadowCat8 suggested seem most useful and explain pricing and architecture choices along with things not even mentioned like peripherals.

Well, I think if we were all stuck in the windoze world, it might make sense to include OS differences since there are distinct levels of support for both services and peripherals depending on which version of the OS you buy from M$. But, I think for the purpose of this thread, OS is a bit superfluous. We're discussing linux, and the key thing to watch out for in linux nowadays is just the differences between x86 and x86_64 (a.k.a. amd64.)

And, @vmccord: Don't feel too bad... At least you didn't date yourself with a reference to the Timex/Sinclair! ;-p hehe
But, if you *really* want to hear differences between some of the older architectures, you may want to find a copy of a computer filk song called "I've Built A Better Model Than The One At Data General". ;) Hehe

I like my Sinclair! And my KIM-1!

(Both of which, BTW, are not for sale.)