IBM PC computer family

The world-renowned computer manufacturer IBM entered the personal computer market with the PC 1050 model, released in 1981. Its global success was due to the modular design of the machine, which made it easy to expand and adapt to the needs (and budget) of the users. Its improved versions (XT, AT, PS/2) became a world standard, and their clones still dominate the personal computer market today. The original models did not become widespread in our country not only because of the high prices paid in foreign currency – at that time the Commodore 64 was the mainstay – but also because SZKI– the first in Europe – came forward with its domestically developed clone called Proper 16 in 1983.

Below we describe the PC XT (top image) and PC AT (bottom image) versions in more detail. Individual data is marked with XT or AT, otherwise it applies to both types.

• payroll
• ?

An example:

• MAIN TAKEH
  
• ?

XT: Information Technology History Exhibition

Structure

Central unit

Byte-organized machine: 8 bpB | 16 bpW

• central control system: microprocessor control + mathematical coprocessor
  • XT: IIntel 8088, clock frequency 4.77 MHz (= 210 ns cycle time)
    • 8-bit internal bus, transfer speed 840 ns (4 cycle times)
    • 20-bit main memory address bus
    • 3×16 bit bus for timing tasks (real-time clock, memory refresh, sound generator)
    • 8 interrupt levels
  • AT: Intel 80286, clock frequency 6 MHz (= 167 ns cycle time)
    • 16|8 bit internal bus, transfer rate:
      • On a 16-bit bus with 16-bit data: 500 ns (3 cycle times)
      • On an 8-bit bus with 8-bit data: 1 μs (6 cycle times)
      • On a 16-bit bus with 8-bit data: 2 μs (12 cycle times,)
    • 24-bit main memory address bus
    • 3×16 bit bus for timing tasks (real-time clock, memory refresh, sound generator)
    • 16 interrupt levels
• main store:

_{In both types of machines, each byte also has a ninth parity bit, which is handled automatically by the system; we will not mention this further.}

• • XT: 128 (max 256) KB RAM (cycle time 345 ns)
    • 40 KB ROM (cycle time 250 ns)
  • AT: 256 (max 512) KB RAM (cycle time 275 ns)
    • 64|128 KB ROM (cycle time 230 ns)
• calculator: fixed-point ALU
  • 16 × 40-bit registers
  • Intel 8087 math coprocessor has 8 × 80-bit registers
• channel:
  • 20-bit data bus for data input/output operations,
    • XT: 4×DMA/20 bit, transfer rate 1.05 μs (5 processor cycles)
    • AT: 7×DMA/20 bit, DMA control clock 3 MHz (= 333 ns cycle time); transfer rate 1.66 μs (5 cycle times)

Periphery

• backups:
  • 5.25″ floppy disk
  • 10MB hard drive
• external (peripheral) devices:
  • monochrome ( Motorola 6845) or color CRT monitor
  • English keyboard
  • 80 chps printer
  • speaker
• Interfaces:
  • 8 external slots for storage and function expansion
    • XT: six 8+32-pin and two 40-pin
    • AT: six 36+62 poles and two 62 poles

Operation

The main memory could be accessed in 64 KB segments – in real (normal) or protected mode – with automatic paging. (The “addressing” – e.g. by indexing – caused a system error.) In protected mode, virtual addressing was possible; then the maximum address range available was XT: 1 MB, AT: 1 GB; the latter also supported the parallel execution of several programs (multitasking).

IBM PCs and their compatible clones operated with the x86 instruction set, the basic version of which was implemented by the Intel 8088 (XT) and Intel 80286 (AT) microprocessors.

8-bit (CISC) instructions have 0-8 additional bits (register addresses, direct data) and 1 or 2 factor addresses (in the case of two-address instructions, the result overwrites the contents of the second address).

Main types of instructions:

• processor:
  • internal data transfer
  • 4 fixed-point basic operations
  • logical operations
  • control operations
  • text management
• coprocessor:
  • unsigned packed decimal and unsigned binary encoded decimal operations
  • signed and unsigned binary multiplication|division
  • floating point addition, subtraction, multiplication, division, square root
  • calculating floating-point exponential, logarithmic, and trigonometric functions

The calculators worked with numbers in the form of sign+absolute value. Data types:

• Word Integer: 16 bits | 4 decimal digits
  • value set: -32.768 ↔ +32.767
• ShortInteger: 32 bits | 9 decimal digits
  
  • range of values: ± 2×10 ⁹
• LongInteger: 64 bits | 18 decimal digits
  
  • value set: ± 9×10 ¹⁸
• Compressed decimal: 80 bits | 18 decimal digits with or without sign
  
  • value set: ± 9×10 ¹⁸
• Short real: 32 bits | 6-7decimal digit
  • range of values: ± 8.43×10 ^-37↔ ± 3.37×10 ³⁸
• Long real: 64 bits | 15-16decimal digit
  
  • range of values: ± 4.19 ×10 ^-307↔ ± 1.67×10 ³⁰⁸
• Current real: 80bit |19 decimal digit
  
  • range of values: ± 3.4 ×10 ^-4982↔ ± 1.2×10 ⁴⁸⁹²

Operation speed: na

Screen management:

• Monochrome:
  • 4 KB RAM buffer, 1.8 MBps
  • 25 lines, 80 chpl, 9×7 pixel characters
  • 256-element character generator
• Color:
  • 16 KB RAM buffer, 1.8 MBps
  • in alphanumeric mode: 25 lines, 40|80 chpl, 9×7 pixel characters
  • resolution in graphics mode: color 320×200, or ff 640×200 pixels
  • 256-element character generator

Program set

• operating system: MS DOS 2. – 3.2, later Windows
• compilers:
  • BASIC (ROM-ba égetve)

Historical curiosities

The legendary 1050 computer was designed by a team of 12 people, including a female computer scientist {!}. “After consulting with Gates, Lowe made a proposal on August 8th for what IBM should create. According to popular rumor … the IBM PC was put together in a mad rush.”

The first version, which cost $1,565, had only 16 KB of RAM (expandable to 640 KB). The machine was developed in close collaboration with two other companies: Intel supplied the microprocessor and Microsoft the operating system. This triad determined the direction of development of business and office computers for decades.

Resources

General Introduction: The IBM PC

Technical description: PC XT, PC AT (amgol)

History of his birth (English)

Historical Overview: How IBM Won the PC Battle

A domestic procurement example

A little PC history