Articles - The operating system on the Spectrum. What is it?

<b>Articles</b> - The operating system on the Spectrum. What is it?

Operating System on the Spectrum. What is it?
by Vitamin


Hello, dear readers!

In this article, such an intriguing title will be affected
Theme operating systems in general and for the Spectrum in 
particular. If you're expecting another advertising a new shell 
or praise non-existent code in the style of the Borg, we can 
not continue read. If possible, I will try to avoid both.

Here we consider a purely technical aspect of this
issue dedicated to designing, developing and, in fact,
work operating systems. I can, I'll even advise
read books on the subject, which of the Spectrum will be no
words. Write this article I was asked the difference in a month
newspaper "Passage" and a group of "Brainwave".

So, turn to the facts. The course "Operating Systems" was
I auditioned at the University of the standard and in front of 
me became such a problem - but is it possible to apply this 
knowledge to our Spectrum? Seeding for the book, one of which 
was NA Oliferov, VG Oliferov "Network Operating Systems", I 
received a lot of additional information from a purely 
theoretical field. When subsequent reading of books on Unix and 
I got Vindouz opportunity to compare these systems and choose 
the optimal solution those or other problems. Next, I will tell 
my thoughts about the interior of the operating system. No need 
to take them for dogma or a pattern. Rather, it merely 
recommendations, some of has been tested in practice. Some part 
of my investigations was published in the Zx-Time. So, I'm in 
something and I will repeat. So, to start to define the basic 
functions who will be assigned to the core of the system:


1) The implementation of multitasking. It includes functions to 
work with processes and allocation of CPU time. Two modes

multitasking - nevytesnyayuschaya and displacing, as well as 
many scheduling algorithms for the latter (for the first, 
incidentally, too) offer unprecedented scope for 
implementation. The question of need to multitask at all, I 
believe, should not be - Too many benefits open when using it in

opposed to the complexity of implementation. Willing to bet - I 
beg my address listed at the end. The only difference between

preemptive and preemptive multitasking is
capabilities of the system call scheduler at the request of the 
process. With preemptive multitasking simple loop can never

hang the system, as it can easily happen if you do not
preemptive multitasking or not at all. In the worst case,
significantly reduced performance. But after removing the "hung"
process, work will continue as usual. Unlike
class processors x86, starting with 386, z80 does not have
hardware memory protection. In other words, no
way can not control the reading or writing in either
memory area. Implementation of "forbidden" code in some
cases can be caught. The only way to protect the core
from invasion of malware is flashing it in Rom.
But this step is justified only in case of a well-functioning 
core, the best appropriate manner possible machines.


2) Work with external devices. These devices can be
anything - from the keyboard and mouse to the DMA and 
GeneralSound. It is only necessary to separate them into 
categories and carry out control in accordance with their 
intended purpose. For example, through disk device driver can 
be accessed holders of various types, ranging from the drive and

ramdisk and ending with hard drive and a CD-drive. For
ensure ease of expansion hardware support system
necessary to provide the Device Manager, which will be
provide a single interface program to access
devices, depending on the category of devices, but does not 
depend of its type.


3) The window envelope. Graphical user interface
nice stuff, but not for the system. For it is the best
interface - a command line. Minimum of resources, nothing more,
single interface of all programs. But try to remember all
Team System! If you do it, you can call themselves a 
professional:) That is why people come up with so-called 
"Intuitive interface", the essence of which - at a minimum 
loading brains user to perform various tasks, albeit at the 
expense of productivity and performance. 

But even here you should not go too far. As an authority
quote from the book of A. Holub, "The rope of sufficient length
to ... shoot yourself in the foot "(Holub.A. Enough Rope To 
Shoot At Your Leg "). This is a book of tricks programming in C 
+ +, but I think you will agree with my decision to include 
this quote. "... The user interface should not be like

computer program (the principle of transparency). I once heard
someone said that the best user interface of
ever developed a pencil. His appointment
immediately clear, it does not need user manual
he was preparing to work without much fuss. However, the most 
important feature is transparency. When you use

pencil, then think about what you write, not about the
pencil. Like the pencil, the best computer interfaces
are those that conceal the very fact that you are addressing
to a computer: a remarkable example of the interface with the 
system ignition of your car. You turn on the ignition,

include speed and presses on the gas, as if all these objects
interface (switch, lever velocity, pedal) were hooked directly
on the engine. Nevertheless, it is not: they are now usually 
just input into the computer that controls the engine. K

Unfortunately, this level of clarity is often lacking in
user interfaces. Imagine a GUI
Windows user on the car. You touch, choosing
main menu item "Movement of the car." Clicking on it opens
Menu switching speed, which will offer you the choice of
option "Forward", "Back" and "Neutral." Click one of the
them to move the box on the direction you want. Then
Go back to "Move the car, and then click
"Let's go." This will bring up a dialog box "Speed"
where you have to use the slider to enter the desired speed.
However, to set the speed correctly is difficult because of the 
high permission of the slider (half a millimeter movement of 
the mouse corresponds to about 1 km / h), so you probably set 
the 59.7 km / h instead of 60. Then you click on "travel" in 
the dialog box, wake for what it says "The parking brake is not 
removed then F1 for Help "(the speaker produces a loud sound). 
You humbly click on "OK" button to remove the message box, then

again trying to open the main menu, but the car just sends
you sound. Finally, realizing that the fact that
dialog box "Speed" still appears, you click on
"Cancel" button to remove it. You open the menu
"The parking brake and put away the box" Enable ". Then again 
you Opens "Let's go." And once again receive the message loud

sound) that you must first choose a direction in the menu
"Switching speed." At this point, you decide that you
may be better to go to work on foot ... "

In general, it is clear that the interface must be 
understandable, but not intrusive. Does not necessarily make a 
shell-like any of the existing interfaces, though GUI framework 
are common to all and set out a long time. Must proceed from 
the specific machines - memory consumption, speed, convenience. 
At the same time, you must provide a single interface to avoid

as on Linux. On it there are several windows
Shells and sets of programs running under a specific
shell. Must be enabled in the kernel and the GUI
provide third-party programmers to write their own shell or
empower the standard.

4) File System. It is a logical nadurovnem
hardware-level media. Physical parameters
media may differ, but the logical structure to remain
constant, as well as vice versa - a physical structure and
different logic. Sufficiently large number of different
file systems is a serious problem of compatibility and
portability. You can also go the way of Unix: the file
system alone. It is determined by two basic concepts: there is 
nothing except the files in the files there is nothing but 
data. Let me explain first concept. All areas of the disk, 
including system area and directory, represented as files. But 
the second concept is a reflection of the first, but already at 
the level of data in files. Also, the main feature of this file 
system, originally known as s5fs, is the absolute tree-file

structure. You may I ask: what about the same
MS-DOS? There, too, a tree-like filesystem. Yes, I agree with 
you I agree, but the point is that such systems

tree is constructed for each logical drive. In all s5fs
differently. Is the main tree, usually located on the system
section. To gain access to other sections and other
drives, it is necessary to mount a file system to
the main tree. Usually it goes like this: create an empty
folder, and it is associated partition. File System
hide these transitions for applications and creates the feeling 
that All files are on one disc. In fact, they can

even physically located on different machines, the network 
serves as a conduit data. Especially, this file system, or 
rather its The logical structure is very compact. In addition, 
the file system provides a single interface for working with 
files and for working with streams, and other input devices and

output. For example, the screen can be represented as a file and
It will display all the information in the teletype mode.

That is, in principle, and all I wanted to tell you about
operating systems. And now, doing their duty:) I,
as requested by the editorial board, talking about his attempt 
to create operating system. I say this about the project ChAOS. 
Home work on it just coincides with the onset of the reflection

What about the OS on the Spectrum. Well, one can not just talk, 
it is necessary try, as it will work in practice. That tasted.

First was implemented multitasking kernel. It works on
scheduling algorithm based on a circular, not too
effective, but the most simple. Also have been written 
procedures scheduling and memory window envelope. Deposits with

disks, you can read the whole file from the disk and 
byte-oriented, write the whole file to disk. So, I could start 
earlier created and saved your application. On this layout, 
debugged many algorithms and test theories. It turned out 
preemptive multitasking real-deal. Everything works, of course, 
is not it quickly as hoped, but faster than expected. In the 
process develop a new algorithm was tested dispatch

based on priorities. But sharpened by the circular algorithm
structure of the system has not given the full test this
algorithm, however, and so it seemed pretty good
results. For interest, I sent this work to Dima Bystrov aka
Alco. It was he told about it all Spectrum population.
Some time later, I started from scratch to write a different 
system in that he tried to collect the best from the old 
version and make a lot of new. At the core was built two modes 
of dispatching CPU time - the circular and priority. Manager

memory was old, but expanded its capabilities. But
Lack of time and the emergence of new and more sensible ideas -
modular structure - made me long to suspend this
project. Now all incoming ideas are written in lyricist for
further deliberation and implementation. Also improved
Modular support until at compile time.

Now gather ideas, and is accumulated material on the new version
system. Work is conducted in conjunction with Maxim Fomkin (MaXx
Fomkin). To tell yet about this new project did not want
but I can say that apart from the world vindouz, spektrumistam
get acquainted with the fascinating world of Unix and Linux:).

With all questions, requests, please contact the following
addresses:

347924 Russia, Taganrog, growth. reg., ul.S.Lazo, 7, kv.54
Gavrilov Vitaly Dmitrievich

e-mail: vitamin_caig@mail.ru