Proudly Serving Iowa

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Iowa Disk Operating Systems since 1980

Store what's important for longevity today into tomorrow.

DOS also as it was called was how one interfaced with the computer by typing commands, programming, creating scripts all a form of instruction as to what one was trying to have the computer perform.  At a lower level these instructions made everything work.

Apple II

The first operating system I used was in 1980 on the Apple II called Apple DOS and used Integer Basic.  The only form of storage available was cassette tape which was inefficiently slow and unreliable.

Atari Commodore 64

Next I programmed on the Atari Commodore 64 which was Commodore KERNAL/BASIC 2.0 GEOS operating system.

Iowa Customers

Some information I know about Iowa is I believe the state was admitted or ratified to the United States around or about 'December 28, 1846'.  Iowa is located around latitude '42.032974' and longitude of '-93.581543' and has a population of roughly '3,190,369 million'.  If I remember correctly the capital is 'Des Moines' and the largest city is 'Des Moines'. 

x86, IBM PC, Compatibles

Then I started programming the Intel x86, compatible CPUs also called IBM PC compatibles which used MS-DOS and IBM PC DOS.  Machine-dependent versions of MS-DOS were produced for many non-IBM-compatible x86-based machines, with variations from relabelling of the Microsoft distribution under the manufacturer's name, to versions specifically designed to work with non-IBM-PC-compatible hardware.  As long as application programs used DOS APIs instead of direct hardware access, they could run on both IBM-PC-compatible and incompatible machines.

The Radio Shack TRS-80's I used ran TRSDOS (which stands for the Tandy Radio Shack Disk Operating System) pronounced 'TRIS-DOS'.

DOS is a single-user, single-tasking operating system with basic kernel functions that are non-reentrant: only one program at a time can use them, and DOS itself has no functionality to allow more than one program to execute at a time.  The kernel of DOS provides various functions for programs (an application program interface), file management, like character I/O, memory management, program loading and termination.

Shell scripting is provided by DOS via batch files (with the filename extension .BAT).  Every line of a batch file is interpreted as a program to run.  Batch files can also make use of internal commands, such as GOTO and conditional statements.

The operating system offers an application programming interface that allows development of character-based applications, but not for accessing most of the hardware, such as graphics cards, printers, or mice.  Programmers were required to access the hardware directly, usually resulting in each application having its own set of device drivers for each hardware peripheral.  Device Drivers for popular hardware was released by manufactures to specifications ensuring drivers were available.

The DOS system files loaded by the boot sector must be contiguous and be the first two directory entries.  As such, removing and adding this file is likely to render the media unbootable.  It is, however, possible to replace the shell at will, a method that can be used to start the execution of dedicated applications faster.

DR DOS

Novell systems used a competitor to MS-DOS called DR DOS.  The boot sector contiguous limitation I mentioned with MS-DOS does not apply to any version of DR DOS, where the system files can be located anywhere in the root directory and do not need to be contiguous.  Therefore, system files can be simply copied to a disk provided that the boot sector is DR DOS compatible already.

If at any point you decide to reach to me just know the area codes I am familiar with for Iowa are '319, 515, 563, 641, 712'.  For Disk Operating System assistance you will find my rates very reasonable for Iowa.  Now just keep in mind my time zone is 'Eastern Standard Time (EST)' and I know the time zones in Iowa are 'Central Standard Time (CST)' in case you wish to call me.  Anyway let me continue.

File System

The DOS filesystem supports 8.3 filenames: 8 characters for the filename and 3 characters for the extension.  Starting with DOS 2 hierarchical directories are supported.  Each directory name is also 8.3 format but the maximum directory path length is 64 characters due to the internal current directory structure (CDS) tables that DOS maintains.  Including the drive name, the maximum length of a fully qualified filename that DOS supports is 80 characters using the format drive:\path\filename.ext followed by a null byte.

Originally the File Allocation Table (FAT) filesystem was originally FAT12 which supported up to 4078 clusters per drive.  DOS 3.0 added support for FAT16 which used 16-bit allocation entries and supported up to 65518 clusters per drive.  Compaq MS-DOS 3.31 added support for FAT16B which removed the 32MB drive limit and could support up to 512 MB.  Finally MS-DOS 7.1 (the DOS component of Windows 9x) added support for FAT32 which used 32-bit allocation entries and could support hard drives up to 137 GB and beyond.

DOS 3.1 was where file redirector support was added.  This was initially used to support networking but was later used to support CD-ROM drives with MSCDEX.  IBM PC DOS 4.0 also had preliminary installable file system (IFS) support but this was unused and removed in DOS 5.0.  Block Devices ("Disk Drive" devices) were also supported by DOS and loaded from CONFIG.SYS that could be used under the DOS file system to support network devices.

I remember writing TSR's which were Terminate and Stay Resident programs which once executed would reside in memory.  A CD-ROM extension like MSCDEX is a good example of what a TSR is.

DOS Memory Management

DOS was originally designed for the Intel 8088 processor which can only directly access a maximum of 1 MB of RAM.  IBM and Microsoft chose 640 KB as the maximum amount of memory available to programs and reserved the remaining 384 KB for video memory, the read-only memory of adapters on some video and network peripherals, and the system's BIOS.  Microsoft believed that the 640 KB barrier would never be reached.  However, by 1985, some DOS applications were already hitting the memory limit, while much of reserved was unused, depending on the machine's specifications

You know, I don't make it out to Iowa much but I would like to see the 'Eastern Goldfinch' state bird.  I am a little familiar with the Iowa 'Wild rose' state flower as well.  However, I do not know much about Iowa's state tree the 'Oak'.  Fishing is fun to me perhaps I would like reeling in the Iowa 'No Official Fish' state fish.  Anyway, sorry I went off topic.  Let me continue.

Later specifications allowed access to additional memory.  The first was the Expanded Memory Specification (EMS) was designed to allow memory on an add-on card to be accessed via a 64 KB page frame in the reserved upper memory area.  80386 and later systems could use a virtual 8086 mode (V86) mode memory manager like EMM386 to create expanded memory from extended memory without the need of an add-on card.  The second specification was the Extended Memory Specification (XMS) for 80286 and later systems.  This provided a way to copy data to and from extended memory, access to the 65,520-byte high memory area directly above the first megabyte of memory and the upper memory block area.  Generally XMS support was provided by HIMEM.SYS or a V86 mode memory manager like QEMM or 386MAX which also supported EMS.

Starting with DOS 5, DOS could directly take advantage of the HMA by loading its kernel code and disk buffers there via the DOS=HIGH statement in CONFIG.SYS.  DOS 5+ also allowed the use of available upper memory blocks via the DOS=UMB statement in CONFIG.SYS.

When Microsoft Windows was developed DOS was still utilized to boot Windows.  It wasn't until later versions of Windows came out that DOS faded away as the boot layer to Microsoft Windows.