Let’s Code MS DOS 0x28: Expanded Memory (EMS)

The original IBM PC and MS DOS could — for the most part — only access 640KB of memory. The LIM EMS standard was at first a standard for RAM expansion cards to overcome this limit. On later machines like the 286 and 386 there was either support built into the chipsets or EMS memory was emulated via drivers like EMM386. Today we learn how to utilize EMS memory to play back an animation that is too large for conventional memory.

Low-Noise 7805/7812 Drop-In Replacements

Linear voltage regulators such as the 7805 and 7812 are ubiquitous in vintage electronic equipment, and especially in home computers of the late 1970s and early 1980s. They have many advantages are very reliable. Their biggest drawback is their heat dissipation. The variants in metal TO3 packages are only available used or as new old stock. So if you want to replace them with a cooler running variant these brand new drop in replacements based on modern switching regulators might be worth a try. These particular variants have extremely low switching noise, so should be very usable in devices such as the Commodore 1541 floppy drive. So we will repair one of my broken 1541s and also fit it with the modern DR340 voltage regulator!