New Student looking For professional Insight

[Steve Bailey]

Sorry Lancie, I can't agree with you on #5. The question was "1K is approximately..."

Well, if you accept the definition that "K" applies to words, not bytes, then 1K is exactly 1024 words, but approximately 1000 words. The answer is d. Isn't the author clever.

Question for peavey wolfgang 2000:
If "K" stands for the prefix "kilo", which means 1000, why does "K" applied to computer memory mean 1024 and not 1000?

 

[TRACY H]

Or Is It

# 5. 1K of memory is approximately?

(a) 1024 bits
(b) 100 bits
(c) 1000 bytes
(d) 1000 Words
(e) 1024 words

I think the answer is C 1K refers to bytes.
1 K is = 8192 bits / by 8 = 1024 bytes
I could be wrong. What do you think peavey wolfgang 2000 I think
this is a good post and they may kick you around a little, but they
will end up helping you. STAY IN THERE:!:

:site:

 

[akreel]

6. Since "prohibitively expensive" is not on the list, I'm going to leave this one blank. I'd guess 32K, if I had to. I don't really care until I approach the limit, or anticipate writing a very, very large program (in which case I'd look up the answer because I needed to know it).

These questions came from a book (or instructor) that must be very dated. My guess would also be 32K if you asked me at gunpoint. But, judging by the relative quality of the rest of the questions, I'd say the guy who wrote them isn't quite in touch with the "real world." They might be looking for 16K as an answer, because that's what Christopher Columbus had for PLC memory.

Mike suggested that we check AB.com on this one. If you do, go look at how much memory is in a 1756 (ControlLogix) series processor. I don't see ANY of those in the choices that were given.

Drop the class. This guy's got tenure!

AK

 

[elevmike]

...Drop the class. This guy's got tenure!

AK, He cant drop the class.. He not taking a class but self studying a book he picked up at a garage sale...

 

[AndyT]

1K of memory is approximately?

As others have stated, depends on the type of memory being discussed. In Direct Logic PLC's (and be willing to bet many others) ladder memory is measured in 8 bit bytes. This is because some instructions take more memory than others and it is not always on 16 bit boundries. If you are talking about Vmemory or registers it is always on 16 bit or 2 byte boundries. So if referencing ladder 1K is 1K bytes. If Vmemory 1K is equal to 2K bytes. I know the question was on AB however could this apply there also?

Andy

 

[Ken Moore]

I'm pretty sure the AB plc's memory is measured in words. When you look at a controller is always gives a listing of words used and words free. So, a 16K processor has enough memory for 16,000 words.

 

[RMA]

I've got to agree with Ron Doran here, with one slight exception - I suspect that some of the earliest comments were the result of people not taking the trouble to read the (whole of the) post.

This, in itself, is not entirely praiseworthy, but it is, perhaps, understandable given some of the student posts we have had recently.

Fortunately, peavey_wolfgang_2000 seems to have the right stuff to brush off the comments (that in itself is a very useful attribute in coping with life as it is, nowadays) and appreciate that by hanging in there (or should that be here?), he still gets the information he requires in the end.

However, having had my own share of off the cuff answers, where I had not read the question sufficiently carefully, I can only hope we all learn from this and read the questions a bit more carefully in future - not jus´t the student questions, either!

 

[rsdoran]

If you are interested in this field then I can offer several options to help you get started:
http://www.plcs.net/contents.shtml

http://www.patchn.com/plcbook.htm

Tutorials on a variety of subjects, electrical, plc..
http://www.sea.siemens.com/step/default.html

Lessons on Electronics and info on devices.
http://www.patchn.com/electron.htm

http://www.freestudy.co.uk

http://people.msoe.edu/~wrate/ee100/programmable_logic_controllers_files/frame.htm

http://www.thelearningpit.com

Let me know if you can use more. If you decide to get a PLC and software to experiment with Allen Bradley offers a Micrologix for approximately $99 with the software available for download.
http://www.ab.com/plclogic/micrologix/1000/

Also checkout http://www.entertron.com Free software and low cost micro plcs.

http://www.automationdirect.com also offers low cost options.

BTW on question #5
Binary kilo is 2 to the 10th power
In computer literature, kilobyte is usually abbreviated as K or Kb. To distinguish between a decimal K (1,000) and a binary K (1,024), the IEEE has suggested following the convention of using a small k for a decimal kilo and a capital K for a binary kilo, but this convention is by no means strictly followed.
http://www.webopedia.com/TERM/k/kilobyte.html

In programming, the natural data size of a computer. The size of a word varies from one computer to another, depending on the CPU. For computers with a 16-bit CPU, a word is 16 bits (2 bytes). On large mainframes, a word can be as long as 64 bits (8 bytes).
http://www.webopedia.com/TERM/w/word2.html

Using that information and assuming from the other questions that the CPU is 8-bit then a word would be 8 bits...ie 1 byte. If using the capital K to mean binary then 1K would equal 1024 bytes therefore 1024 words for an 8-bit CPU.

The ambiguity continues.

 

[akreel]

AK, He cant drop the class.. He not taking a class but self studying a book he picked up at a garage sale...

Sure enough... OOPS! Should've looked at page 3.
Our newest self-starter jumped right in with both feet. Perhaps newer material would be in order.

I wanted that to be a general statement, though. If there are other students reading, don't PAY somebody to ask you questions like this. Take a different class.

AK

 

[TRACY H]

Think About It

I'm pretty sure the AB plc's memory is measured in words. When you look at a controller is always gives a listing of words used and words free. So, a 16K processor has enough memory for 16,000 words.
__________________

I could be wrong and have always (assomed) like you Ken, but when you do the math. 16k equals 8192 words in base 2. The K is in ? here as cpu momery is in KB. Now if the K stands for 1000 OK if the
K stands for k bytes that`s different. If this kid is asking questions like this and in high school he`s probably going to do all right. Plus he came back after a good thrashing.
GO FOR IT wolfgang

 

[Gerry]

bytes, words, and K's

When talking about A-B processors, all K's are binary, all words are 16-bit, and bytes are bytes are 8-bit.

For all A-B processors prior to ControlLogix, a K of memory meant 1024 16-bit words.

In ControlLogix, memory is measured in bytes (Megabytes!)

I agree with Steve's comments about the book's author - too clever by half. The questions are ambiguously worded, semantically convoluted, and appear designed to confuse rather than elucidate. Besides that, the answers amount to no more than trivia.

However, if the book has sparked an interest in Wolfgang to enter what can be a challenging and rewarding profession, then it's not all bad. And, just maybe, one day he'll be able to whip up a serving of 'crow' for Master Woods.

 

[AndyT]

When talking about A-B processors, all K's are binary, all words are 16-bit, and bytes are bytes are 8-bit.

Does AB tell you how much memory a common output coil will require as compared to a complex function? I have little experence with AB, just asking the question.

Andy

 

[Terry Woods]

Wolfy...

The very fact that you came back and clarified your situation and then, argued your position and then, continued by explaining your reasoning for your answers shows me (but then, who the hell am I?) that you are serious.

I extend my apology... if you will accept it.

The best advice so far is that from Steve... lose your current book. Read Phils's free book and consider buying his extended hard-copy version... and maybe the videos!

Another thing you might consider doing is going to Radio Shack and buy a couple of their pocket-books on Understanding Computer Science (the one I have has Radio Shack Part Number 62-1383, this is quite old), and Digital Logic (don't have the PN handy).

Each book is about a 1/2" thick. These books present a light (but not too light) intro into the fundamentals of computer science and digital design. (I'm not referring to the books by Forrest Mims... although those can be a lot of fun.)

The reason I suggest these books is because they will teach you the basics of digital design. Most PLC books do not provide this kind of substance... at least, not in the same manner nor to the same extent.

I used to think that if a guy could program one PLC he could program any PLC... these days, I realize that my belief was based on the assumption that the given programmer knew the basics of digital design.

I now know that many programmers know the more complicated aspects of digital design only to that extent provided by the special functions incorporated in the particular PLC that they learned on. That is, they can produce the desired effect only as long as the particular special function instruction is available.

If they then move on to another PLC they might or might not be able to reproduce a particular familiar effect if the particular, familiar, special function is no longer available.

All special function instructions in any PLC are based on the basic instructions available in any (upper-end) PLC. Any complicated effect can be produced by the basic set of instructions if the programmer understands how the basic instructions can be logically manipulated to produce the desired effect.

So, in addition to becoming familiar with PLCs in general, my suggestion is to learn digital logic in a manner that will open all PLCs to you... not just the one you will have learned on.

I seriously wish you good luck and invite you to bombard us with questions (questions with reasonable explanations of your understanding up to that point... as you have done thus far).

 

[peavey_wolfgang_2000]

Sorry Lancie, I can't agree with you on #5. The question was "1K is approximately..."

Well, if you accept the definition that "K" applies to words, not bytes, then 1K is exactly 1024 words, but approximately 1000 words. The answer is d. Isn't the author clever.

Question for peavey wolfgang 2000:
If "K" stands for the prefix "kilo", which means 1000, why does "K" applied to computer memory mean 1024 and not 1000?

To answer Steve's Question.....Well growing up I had a Commodore Vic 20 & 64 and the memory was always refered to as K, for example a vic 20 had 3K memory and a 64, well 64K, besides that I have no knowledge on the subject, I am aware the the abbrevation for K or "kilo" equals 1000, so my inital thought was leaning towards 1000 bytes due to the word Approx......but besides that i learned many years ago that when i powered up my computer (vic 20) across the top of the screen it read 3072 free bits....divide that by 3, you get 1024 bytes in 1K, But I guess for all of these years when people ask how much memory was in my Vic i should have replied "Yea it got 3 Kb!!!!!"

 

[Thomas Sullens]

ok

Told you they would come around wolfgang. Their serious all they had to find out is if you were.

3072 free bits....divide that by 3, you get 1024 bytes

, but 3072 bits ain`t equal to 1024 bytes is it?