Home
Man
Search
Today's Posts
Register

This forum is closed for new posts. Please post beginner questions to learn unix and learn linux in the UNIX for Beginners Questions & Answers forum.

trying to understand rationale of unix stream i/o concept

Tags
beginners

 

 
Thread Tools Search this Thread
# 1  
Old 07-11-2009
trying to understand rationale of unix stream i/o concept

I am an entry level programmer with no formal training in computer science. I am trying to enhance my conceptual knowledge about operating systems in general.

I have been using the C programming language on Linux systems for some time and have used the traditional unix stream I/O APIs. The introductory material in books and on the web, typically introduce the unix stream I/O model as "basic unix I/O model is a stream of bytes which can be accessed sequentially or randomly". I understand this part, but I am unable to visualize how else would one access the data. Were the I/O models different before the I/O stream model came in to existence? Are there models in current computing paradigm which are different from the stream I/O. I will appreciate if some can help me visualize both the stream I/O model vs other models (if they exist or existed). Pros-Cons will be a great addition too.

In addition, I came across the following statement on the web (I/O System)

"The basic model of the UNIX I/O system is a sequence of bytes that can be accessed either randomly or sequentially. There are no access methods and no control blocks in a typical UNIX user process."

I do not understand the last statement - what are access methods and control blocks in the context of I/O?

Thanks
Kay
# 2  
Old 07-16-2009
A method is like a subroutine. An example might be a file of dictionary words. Instead of writing. you "insert" the word. Somehow the system keeps the words in alphabetical order. You can retrieve a list of all word in alphabetical order or you can search for a word. But the data file itself is a black box and you can't access it. If you put 1,234 bytes worth of words into the data file it will be bigger than 1,234 bytes. The system needs some extra stuff to find it's way around the file. This extra stuff is the control blocks.

And believe it or not, there used to be a sequential file which behaved like a really stupid tape drive. You could read it. You could even read it byte-by-byte. But after you read, say, byte number 123, you had two choices: read byte 124 or close the file. However, the OS could predict a program's behavior rather easily and this was fast (for it's day).

There might be a "random" file where you could seek and then read, but it was slow. After seeking to byte 123 and reading one byte, you could next seek to byte 124 and read that. But if you wanted a sequential file, you were supposed use a sequential file, not a random file.

Mind you, a single data file might be opened as "sequential" by one program and "random" by another. But then each program had a different interface (or subroutine or method) to read the file. However there was no way to execute a data file or to read a program file.

There were many file types and OS's competed by offering more file types. The Unix model of just one file type displaced all of this.
 

« Previous Thread | Next Thread »
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

More UNIX and Linux Forum Topics You Might Find Helpful
Thread Thread Starter Forum Replies Last Post
How to Understand the UNIX Time Format? babinlonston Red Hat 4 06-12-2014 07:31 AM
Stream manipulation in UNIX shell scripting Acme Shell Programming and Scripting 4 08-09-2013 01:59 PM
What exactly is the concept of BITS in this unix.com forum? Manjunath B What is on Your Mind? 2 09-28-2012 06:05 AM
Plan9 sed - rationale for limitations uiop44 UNIX for Dummies Questions & Answers 1 08-04-2012 10:05 PM
Understand a old unix shell script kam786sim Shell Programming and Scripting 2 02-10-2011 01:20 PM
Regarding Mail concept in unix krishna_gnv Shell Programming and Scripting 3 08-30-2010 10:48 AM
[Video stream] network stream recording with mplayer takeo.kikuta Shell Programming and Scripting 1 04-08-2010 04:06 AM
don't understand the unix script pochaman UNIX for Advanced & Expert Users 1 11-17-2008 10:47 AM
Having difficulty with UNIX concept. Please help! ALon UNIX for Dummies Questions & Answers 4 01-11-2007 11:42 AM


All times are GMT -4. The time now is 02:49 PM.

Unix & Linux Forums Content Copyright 1993-2018. All Rights Reserved.
UNIX.COM Login
Username:
Password:  
Show Password