history of computing – Observations from Uppsala

Reversing out of Reverse

The Intel Simics simulator version 7 removed a long-standing feature from the simulator framework. Reverse execution is no longer available. In its place, in-memory snapshots were introduced, which arguably offer most of the benefits at a lower implementation cost. What happened? I’ve been asked about the reasoning behind the chance on several occasions since I left Intel. I’d like to share my perspective on the decision, as it highlights the challenges of turning an idea into a robust, shippable feature.

“Processor Performance Insights and Optimization” – Computer and System Architecture Unraveled Event Four

Finally, the fourth CaSA, Computer and System Architecture Unraveled, meetup happened on November 6. It took far too long to get it organized, but we finally did it. The theme was about processor performance analysis and efficient processor implementation, offering two talks from very different perspectives. The location was almost the same as before, on the 19^th floor of the Kista Science Tower building. Once more thanks to the sponsorship from Vasakronan and Kista Science City.

Useful Instruction Set Computing

I tend to get into discussions about computer processor instruction-set architecture (ISA) design. ISA design is far from my day job, but it is an interesting topic where everyone working with computers at the machine level have opinions. Typically based on a mix of personal experience and fond memories of particular machines. This in turn leads to intricate and intriguing arguments. In this blog, I will talk about my take on the current state of instruction sets in industry and the age-old “complexity of instruction set” question.

Code to the Spec(trum) or the Implementation

When writing software that uses any kind of API or hardware functionality, sooner or later there will be questions about what a particular API call or hardware operation is supposed to do. In principle, such questions should be answered by referring to the specification (and user documentation). I am a firm believer in writing readable and clear specs and keeping software coding to follow the spec, as that ensures future compatibility. But reality is not that simple. Things are generally better today than they used to be, though. Reading up a bit on the history of my first computer (the ZX Spectrum), I found some rather interesting cases of spec vs implementation, and “discovered functionality”.

Thank You, Sir Clive Sinclair

A few days ago, Sir Clive Sinclair died. I owe him, or rather his most successful product, my career as a computer scientist. I bought myself a ZX Spectrum in my early teens, taught myself how to program it, and never looked back. The ArsTechnica obituary calls the Spectrum a “gaming computer”, and I guess that is mostly fair. Can’t say I ever used it for more than playing games or programming games.

Timesharing System Design Concepts (1970)

When I recently turned 50, a friend of mine gave me a book that was about as old as me – Timesharing System Design Concepts, by Richard W Watson. The copyright date is 1970, but the publishing date found online 1971. The book covers the hardware support and software techniques needed to provide multiple users with simultaneous access to a computer system. Typically, using remote teletype terminals. It is a wonderful book, reflecting on the state of computer technology around 1970. It shows both how many of the basic concepts we still use today were already in use back then, but at the same time just how far we have evolved computing since.

Professor Reinhard Wilhelm on the History of WCET Analysis

Back when I was a PhD student working on worst-case execution-time (WCET) analysis, one of the leading groups researching the topic was the “Saarbrücken gang” led by Professor Reinhard Wilhelm. Last year, Professor Wilhelm published a retrospective look on their work on WCET in the Communications of the ACM. It is a really interesting history write-up from the perspective of the Saarbrücken group.

The First Swedish Programmer (1790s)?

The history show (and podcast) of Sverige Radio, Vetenskapsradion Historia, is one of the shows that I subscribe to and listen to regularly. In their look back at 2020, they reminded me of an episode from back in the summer that indirectly introduces what I believe to be the first programmer in Sweden.

DOOM Black Book – This is Brilliant!

I heard about the DOOM Game Engine Black Book by Fabien Sanglard on the Hanselminutes podcast episode 666, and immediately ordered the book. It was a riveting read – at least for someone who likes technology and computer history like I do. The book walks through how the ID Software classic DOOM game from 1993 works and the tricks and techniques used to get sufficient performance out of the hardware of 1993. As background to how the software was written, the book contains a great description of the hardware design of IBM-compatible PCs, gaming consoles, and NeXT machines circa 1992-1994. It covers software design, game design, marketing, and how ID Software worked.

Borland Turbo Debugger – Reverse Execution in 1992

Thanks to a tip from “Derek” on a previous blog post about a replay debugger from 1995, I was made aware of the reverse execution ability that was available in the Borland Turbo Debugger version 3.0 from 1992! This is the oldest commercial instance of “reverse” that I have found (so far), and definitely one of the oldest incarnations of the idea overall. Thanks to Google and the Internet, I managed to find a scanned copy of the manual of the product, which provided some additional information. Note that the debugger only does reverse execution, but not reverse debugging since you cannot run in reverse to stop at a breakpoint.

Continue reading “Borland Turbo Debugger – Reverse Execution in 1992”

Intel Blog Post: Interview with Bengt Werner on the Early Days of Simics

Bengt Werner was one of the first people to work on the simulator that would become Simics, way back in 1992. On my Intel Blog, I published an interview with Bengt a while back where we discuss the early days of Simics and the original product vision and use cases.

Continue reading “Intel Blog Post: Interview with Bengt Werner on the Early Days of Simics”

Intel Blog Post: The Simics Fulprompt, Fulöl, and Fuldans

I have a new blog post up at the Intel Developer Zone, this time about the Simics “fulprompt”. Every software team has its legends about spectacular mistakes, crazy users, and customer calls with strange questions. The Simics “fulprompt” is one example of this from the early days of Simics. It was a prompt that appeared where no prompt would normally appear, right in the middle of executing an instruction. As such, it was an ugly hack… and for Swedes who were around in the 1990s, the only name for a ugly hack is a fulhack.

Continue reading “Intel Blog Post: The Simics Fulprompt, Fulöl, and Fuldans”

Intel Blog Post: Fault Injection in the Early Days of Simics

Injecting faults into systems and subjecting them to extreme situations at or beyond their nominal operating conditions is an important part of making sure they keep working even when things go bad. It was realized very early in the history of Simics (and the same observation had been made by other virtual platform and simulator providers) that using a virtual platform makes it much easier to provide cheap, reliable, and repeatable fault injection for software testing. In an Intel Developer Zone (IDZ) blog post, I describe some early cases of fault injection with Simics.

Continue reading “Intel Blog Post: Fault Injection in the Early Days of Simics”

Intel Blog Post: Simulation a Thousand Target Machines – in 2004 and 2018

Back in 2004, the startup Virtutech built a crazy demo for the 2004 Embedded Systems Conference (ESC). Back then, ESC was the place to be, and Virtutech was there with a battery of demos to blast the competition. The most interesting demo from a technology perspective was the 1002-machine network, as described in an Intel Developer Zone blog post of mine.

Continue reading “Intel Blog Post: Simulation a Thousand Target Machines – in 2004 and 2018”

Intel Blog Post: Running Large Workloads on Simics – in 1998 and 2018

I have just released a new blog post on my Intel Developer Zone blog, about how Simics runs ~~large~~ huge workloads. I look back at the kinds of workloads that ran on Simics back in 1998 when the product first went commercial, and then look at some current examples running on Simics. This is the first post in a series intended to celebrate 20 years of Simics as a commercial product.

Continue reading “Intel Blog Post: Running Large Workloads on Simics – in 1998 and 2018”