Blog

Calculator

By Henry, on August 13th, 2023

As a computer engineer, I often do calculations with a mix of decimal and hexadecimal numbers. But I haven’t been able to find a calculator that can work in both bases conveniently. So I wrote one. . . . → Read More: Calculator

Lenovo Thunderbolt Dock Type 40AC

By Henry, on August 7th, 2023

The Lenovo Type 40AC dock is a Thunderbolt 3 dock that is capable of USB Power Delivery changing. However, getting the 40AC dock to charge over USB PD requires at minimum a 135W AC adapter, regardless of how much USB charging power is actually being used. When using a smaller AC adapter, the dock will function but refuse to charge, and the red LED on the Thinkpad logo will continuously flash. . . . → Read More: Lenovo Thunderbolt Dock Type 40AC

Depstech DW49 Webcam — Teardown and Measurements

By Henry, on July 6th, 2022

The Depstech DW49 is a low-cost webcam that claims to record 4K 30 fps video. I recently got one “used” from eBay for $30, so I can find out what’s inside by disassembling it and making some measurements.

“4K” cameras at this price point often use a lower-resolution image sensor and then scale up the image to 4K, resulting in a video with the right number of pixels, but a blurry picture. The DW49 also upscales 4K video (8.3 MP) from a lower-resolution sensor region (5.2 MP), but the difference from reality is less than some other “4K” cameras I’ve seen, and is a step up from Full HD (2.1 MP). Overall, not quite as advertised, but not bad for the price.

Capacitors in storage can get the plague too

By Henry, on February 22nd, 2022

Capacitor plague refers to defective capacitors that would generate gas, swell, and rupture with age. I bought some Nichicon HM series electrolytic capacitors (made in 2005) to replace plague-afflicted capacitors on an old PC motherboard. These replacement capacitors (apparently also defective) have now swollen again and some ruptured. Out of 169 “new” capacitors still in the bag, almost 70% of them were swollen, despite never having been used…

So the next logical thing to do is to experiment on them: Take some measurements, charge them up, and see how the capacitors respond, why they failed, and whether any of them are still usable. (Spoiler: None are still usable.)

. . . → Read More: Capacitors in storage can get the plague too

Portland Black Lives Matter Mural

By Henry, on August 16th, 2020

I tried to photograph a “Black Lives Matter” mural by stitching together 617 photos. . . . → Read More: Portland Black Lives Matter Mural

Elections 2019: Who is really getting a tax cut?

By Henry, on October 19th, 2019

It’s Canadian federal election season again, and that means party platforms and arguments about tax cuts, deficits, and how much each campaign proposal will cost. As usual, the Office of the Parliamentary Budget Officer (PBO) provides independent estimates of the cost of campaign proposals.

But the cost to government is only one half of the . . . → Read More: Elections 2019: Who is really getting a tax cut?

Discovering Hard Disk Physical Geometry through Microbenchmarking

By Henry, on September 6th, 2019

Modern hard drives store an incredible amount of data in a small space), with billions of sectors (with thousands of defects), packed into hundreds of thousands of tracks spaced tens of nanometers apart, arranged onto a stack of platters spinning around at a high speed. Which drive characteristics can be discovered using microbenchmarks?

This article describes several microbenchmarks that try to extract the physical geometry of hard disk drives, and a few other related measurements, including rotation period, the physical location of each sector, track boundaries, skew, seek time, and locations of defective sectors. I use these microbenchmarks to characterize a variety of hard drives from 45 MB (1989) to 5 TB (2015).

A Cardboard Haswell Box

By Henry, on December 3rd, 2018

This post is about a cardboard computer I built in 2015. It served as half of my simulation cluster during the latter half of my Ph.D. work. This is a continuation of a series of cardboard computer cases I’ve built (2014/2012, 2010). Compared to the previous boxes, this one packs even more systems (8 quad-core Haswells) into a box, while still sharing one power supply. . . . → Read More: A Cardboard Haswell Box

The Microarchitecture Behind Meltdown

By Henry, on May 18th, 2018

Since the recent (Jan. 2018) disclosure of the Meltdown vulnerability, there has been a lot of interest, speculation, and hysteria, but not a particularly good understanding of the processor microarchitecture feature responsible for it. Understanding of the root cause of the vulnerability allows one to understand why only some microarchitectures are affected, and allows reliably testing for the existence (or, even harder, the non-existence) of the vulnerability on various processors, instead of relying solely on vendor self-reporting (or worse, speculation…).

This article first defines the microarchitectural mechanism that allows Meltdown to work, then develops a microbenchmark to specifically test for this behaviour on multiple microarchitectures.

. . . → Read More: The Microarchitecture Behind Meltdown

PET is hygroscopic: Water diffuses out of a Sprite bottle

By Henry, on April 18th, 2018

Polyethylene terephthalate (PET) is a plastic commonly used to make beverage bottles. PET is hygroscopic . Therefore, if you have a bottle of Sprite, you would expect the water to be absorbed by the plastic, diffuse through the bottle, then evaporate outside the bottle.

And that’s exactly what happens.