IBM AT 5170

"The Birth of the New Standard"

Introduced in August 1984 and discontinued in 1987, the IBM Personal Computer AT (model 5170) created a new standard in the computer market of the 1980s. Shortly after its release, it was vastly imitated by other PC manufacturers. Based on the 16-bit Intel 80286, the IBM AT offered many innovations such as EGA graphics, 16-bit expansion slots, and the 1.2MB 5.25" floppy disk drive. In April 1986, IBM upgraded the 5170 by replacing the 6 Mhz CPU with an 8 MHz 80286.

• The IBM AT sold more than 100,000 units
• It was initially sold for $6,000 ($16,700 in today's money)

IBM 5170 AT A GLANCE

• PC-Dos 3.0 operating system (Capable of running MS-DOS up to 6.22)
• 80286-2 processor running at 6.0 MHz or 8.0 Mhz
• Built on a huge case containing 8xISA expansion slots and 3 bays for placing FDD/HDD
• 512K RAM (can be upgraded up to 16MB via a memory expansion card)
• Built-in Cassette Basic (can be used for setup)
• EGA Graphics (16 colors on screen, compatible with CGA and Hercules)
• Built-in 1.2MB 5.25" floppy disk drive (Y-E Data model YD-380)
• Support for 720K 3.5'' floppy disk drives -Note that only later models support 1.44MB 3.5'' disk drives
• Built-in hard disk 20/30 MB (CMI model 6426-S)
• Initially, it came with a 5-pin model F mechanical keyboard (84-key layout), later models came with a model M keyboard (101-key layout)
• Built-in keylock on the front which may disable the use of the keyboard

All IBM AT 5170 models

There were different models of the IBM 5170. As presented below, IBM released 3 different motherboard types with several sub-models.

Notes

• A 16-bit MFM controller was the stock card for the later revision 8MHz AT
• AT probably means 'Advanced Technology'

IBM AT 5170 Motherboard Variations

• There were 3 main motherboard variations

IBM AT 5170 Sub-Models

• These are the sub-models:

Operating System & Set-UpThe IBM PC/AT operating system was based on the classic MS-DOS.

• PC-DOS 3.0 as default
• Capable of running MS-DOS from 1.0 and up to 6.22
• Alternatively OS/2 1.x or XENIX
• Capable of installing MS Windows 1.0-3.1
• Note that there is a 'Cassette Basic' built into the IBM 5170 motherboard
• If there is no FDD/HD to boot from, the 5170 boots to 'Cassette Basic'

When you add a new device, the IBM 5170 needs a setup. These are the three different setup methods:

3 Different IBM 5170 Setup Methods

• METHOD 1 -BY PLACING THE IBM AT DIAGNOSTICS 5.25 FLOPPY (more information here)
• METHOD 2 -BY PLACING A FLOPPY WITH THE 3d PARTY GSETUP PROGRAM (more information here)
• METHOD 3 -BY TYPING CODE INTO BASIC (No Floppy needed -more information here)

Graphics and Cards

The IBM AT line of computers offered for the first time EGA graphics (expansion slot).

• IBM introduced EGA in October 1984
• The IBM AT could be equipped with CGA, MDA, EGA, or PGA video cards

EGA (Enhanced Graphics Adapter)

• EGA can show 16 colors on the screen (64-color palette)
• EGA (640×350 pixels) with 16 colors
• Compatible with 
  • CGA (640×200 pixels) with 4 colors
  • Hercules (720×348 pixels) monochrome

Sound Capabilities

The IBM AT computers had no extra sound hardware than the classic PC speaker.

• Loud PC speaker (placed on the front)
• By placing an Adlib or Soundblaster card you can easily improve the sound of 5170

IBM 5170 I/O Ports, Sockets, and Switches

The only built-in port of the 5170 is the AT keyboard port on the back of the case. Note, that 5170 also supports IBM PC/XT keyboards.

• Battery-backed real-time clock (RTC) built into the motherboard (Motorola MC146818) -The RTC includes 50 bytes of CMOS memory which stores BIOS parameters
• Socket for adding an 80287 math co-processor
• The AT has no DIP switches on the motherboard as in the case of PC/XT, there is only a Display Switch

IBM 5170 Monitors

The IBM AT came with an EGA color monitor supporting CGA and Hercules modes:

• IBM 5154 EGA Color Monitor
• Alternatively IBM 5151 (green monochrome), 5153 (CGA color), and 5175 (PGA color)
• By placing a VGA card you can connect the 5170 to any CRT/LCD/TFT VGA monitor
• There is a Display Switch in the motherboard for changing to EGA/CGA/MDA, according to your monitor type

Expansions & Upgrades for the IBM AT

Basic Upgrades (for its time)

• A 128K memory upgrade to 640K (standard for its time, requires a memory expansion card)
• Math co-processor chip, the Intel D80287 (available socket inside)... running at 6, 8, or 10 MHz
• 2nd internal Floppy Disk Drive (All 5170 models can handle 720KB 3.5 drives, but only later revisions can easily handle 1.44MB 3.5 drives)
• For placing any 3.5 drive... you need a 5.25/3.5 case plus an IDC adapter (Edge connector to 34-pin IDC floppy adapter) and a Molex cable (Molex male to FDD female)
• Game card for adding 2 x 15-pin joysticks

Modern Upgrades

• Up to 16MB memory upgrade (requires a memory expansion card)
• VGA graphics card (works fines with all monitors)
• Adlib or Soundblaster sound cards (or clones)
• IDE hard disk based on a CF/SD card -Depending on the card, you may need to upgrade your BIOS
• Gotek USB drive (Needs the same adapters as any common 3.5 FDD, check above)
• ROM upgrade (more here)
• RTC replacement (6V can be achieved with a case of 4x1.5V batteries) -Note that you need to go through the Setup Procedure explained above

■ IBM 5170 AT Computer

BinaryValue.com (c)

Video Tutorials:

• https://www.youtube.com/watch?v=yyL_a9QE8ag

Sources:

• https://en.wikipedia.org/wiki/IBM_Personal_Computer_AT
• https://minuszerodegrees.net/
• https://retrocmp.de/ibm/5170/5170-t3.htm
• https://ancientelectronics.wordpress.com/2021/06/28/ibm-at-5170/
• https://www.dosdays.co.uk/computers/IBM%20PC-AT%20(5170)/ibm5170.php
• https://www.pcjs.org/machines/pcx86/ibm/5170/