I was there - a young working engineer who has a low serial number IBM PC (16K RAM with an audio cassette interface for "Mass Storage" - no floppy or HD) and the Honest-to-god 51st IBM AT to come off the line in Boca Raton, for which I slept on a sidewalk for two days in Boca Raton in order to buy, for $4000, a receipt allowing me to purchase one when they came available!
Back then I built test equipment cards / wrote software to test our products on the PC and testing multiple Aviation RS422 busses at 12.5kbps REQUIRED working very "close to the metal" as the anemic 8088 and the marginal IBM PC BIOS serial routines tapped out just a little above 9600 Baud.
I memorized the IBM Technical Reference manual. As an add-on developer I legally got to see, and modify that BIOS code, on the fly, from my application working directly with chips and registers (i.e. "bare metal).
Working just above the metal meant writing Interrupt handlers for the 8259 PIC controller, at which point MY code owned the Computer outright and BIOS was an application I had to keep happy (instead of vice-versa)! To me that is the purest definition of "Close to the Metal".
I had to not only to service my expansion card hardware, but my programs had to respond to every interrupt, and do callbacks to everything IBM to keep the keyboard, clock, disks, video, etc. EVERYTHING running. Trust me when you take control of the 8259 interrupt controller, there are a LOT of ways you can "Halt and Catch Fire" beyond just executing that opcode!
COMPAQ was the 4th, and best portable I worked with - and stayed so for many years after.
I write most of my posts from memory, but believe in backing up my text with citations.
Exciting to be reliving this -- and validating some of the stuff in the show.
Love the look of the Wiki - was searching for any Historical basis for Cardiff, found you site, got jazzed by the look and feel, hope you don't mind, but maybe I'll stick around for a while