---
layout: post
title: The 8Mhz IBM PC AT 5170
date: 2014-10-13 11:00:00
category: JavaScript
permalink: /blog/2014/10/13/
---

I just added my first [8Mhz IBM PC AT](/devices/pcx86/machine/5170/ega/1152kb/rev3/debugger/) machine configuration
to the list of [IBM PC Machine Configurations](/devices/pcx86/machine/), and not surprisingly, the new machine
fails to boot.

This machine uses the 3rd [ROM BIOS](/devices/pcx86/rom/5170/) that IBM released for the PC AT, a revision that
included support for 3.5-inch 1.44Mb diskettes -- which will be nice, because I have a number of 1.44Mb diskette
images I would like to be able to read in a PCjs machine.

Since machines with this BIOS also ran at 8Mhz, I've bumped the CPU speed up to 8,000,000 cycles/second.
It'll be interesting to see whether this BIOS also increased any of its hard-coded timing delay-loops as a result.

Anyway, when I enabled ChipSet I/O port messages in the Debugger:

	m chipset on
	m port on

I can see that the BIOS Power-On Self Test (POST) progresses nicely until it starts generating lots of port 0x61
activity:

	chipset.inPort(0x0061,8042_RWREG): 0x30 at F000:05A8
	chipset.inPort(0x0061,8042_RWREG): 0x20 at F000:05AE

I know what I'm going to be doing this afternoon now.

*[@jeffpar](http://twitter.com/jeffpar)*  
*October 13, 2014*