11

About 0.6 to 1 ms after the last one is read. The 8042 keyboard controller does not queue scancodes; it just stops receiving bits from the keyboard until a byte is read from port 0x60. When a scancode byte is read out, the controller gets ready to receive another byte from the keyboard. But since serial communication is not instantaneous, actually receiving ...


9

[Caveat, this is from memory, and about a real PC-AT, with real, 16 bit BIOS and code] TL;DR: When does an IBM-compatible PC keyboard controller dequeue scancodes? (I assume this is about a PC-AT, not a PC or PC-XT) Never, as there is no queue. At least none in hardware. The 8042 has simply 4 registers Data In/Out, Status and Command. All synchronisation ...


8

Looking at the pictures on iFixit, the two PCBs that fit behind the shoulder buttons don't seem to be reinforced by anything much: Excess pressure on the shoulder buttons might bend these boards slightly away and cause the connection to not be made. The alternative is corrosion on the connection traces; you say you have tried contact cleaner. Try bending ...


5

Several sources around the web repeat the notion that the VT05 was a "drop-in replacement" for the (ASR33) teletype. For example, on gunkies.org: The VT05 Alphanumeric Display Terminal (technically, the VT05B, but documentation usually referred to it as the 'VT05') was one of DEC's first video terminals. It supported all the same format control ...


5

A bit of googling finds that SMC is "Standard Microsystems Corporation", apparently got renamed at one time to SMSC and finally to "Microchip". The FDC37C654 is a Super-I/O chip with a floppy disk controller, hard disk controller, two serial ports, and a parallel port. The datasheet can be found e.g. here from this page (not sure how ...


2

This card is a low-cost model. The PCB is actually designed to take the more modern FDC37C666 chip, but on the card shown in the original post, the older (but mostly compatible) FDC37C654 is equipped instead. The two jumpers labelled FDD (JP5 and JP6) are most likely: FACF - pin 26 - not a configuration pin on the '654. Position doesn't matter FDCCF - pin ...


2

Did you try opening the drives up and giving them a good cleaning with isopropyl alcohol first? Sometimes the problems with old floppy drives is mechanical. Their step motors get stuck, or the lube on the screw drive dries out and the heads can't move. Make sure the heads are able to move with a little nudging. Clean them gently with a cotton swab. (Don't ...


2

In the 1960s, many major languages such as FORTRAN and COBOL specified a line length of 72 characters. This was largely due to the limitations of the 80 column punch cards with which they had been originally programmed. An IBM punch card used 8 columns for a sequence number, leaving 72 to encode characters. This practical limitation was enshrined in the ...


1

Almost all these old machine did have SOME ventilation. The BBC seems to have less than normal, but there are some ventilation slots underneath, and on the back on some of them. That said, it does seem to have less than similar systems of the era. The fact is - those old 70s/80s home computers just didn't run as hot as modern Intel/AMD systems! Your typical ...


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