PC/DOS Overview
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PC/DOS Overview

Overview of PC and DOS


The first generation of microcomputers are comprised the initial wave if small computers targeted for the hobbyist. The second generation refers to 8-bit computers with from 4K bytes to 64K bytes of RAM. In this generation, some software was burned-in to ROM and in most cases, it was a ROM monitor and with a larger RAM size. This generation systems also support hard disks in some configurations. In a nutshell, the fourth generation will include multi-user capability, possibly 32-bit microprocessors and virtual storage facilities.

ROM Monitors

The objective of a ROM monitor is to provide enough software to read a program into a microcomputer and run it. Without software, a microcomputer is a dormant piece of hardware incapable of responding to the press of a key and of sending a character to the display console.

A ROM monitor ties together the basic input and output functions and allows the user to enter simple commands to the computer. The standard functions supplied by most microcomputer monitor systems are include in the following list:

  • Load a program into RAM from the keyboard
  • Display contents of RAM
  • Modify contents of RAM
  • Initiate program execution
  • Save the program from RAM on cassette
  • Load a program from cassette tape to RAM
  • Print information stored in RAM

Most ROM monitors are less than 1000 bytes long and are place along with a BASIC interpreter on a single ROM chip. ROM is designed to be a lower extension of RAM so that the program counter, which is set when the computer  is turned out, points directly to a monitor routine in ROM. Thus the computer comes to life automatically when the on button is pressed.

Disk Operating System

The relative slowness of cassette storage quickly led to the development of diskette storage. The need to provide access to diskette storage in a "user friendly" manner gave birth to the Dis Operating System (DOS), which did little more than to support I/O operations, in addition to performing the ROM monitor functions , covered above. The use of disk storage, however resulted in the need for a variety of utility programs such as the following:

  • Format a diskette
  • Copy a diskette
  • Erase files
  • Copy files
  • Print files

Most disk operating systems contain a resident and a non-resident part. The resident part is bootstrap loaded from diskette when the computer is turned on and the transient routines are read in when needed.

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Comments (1)

Yes, I have been there for the earliest DOS computers, how life has changed!!