1. SINCLAIR ZX SPECTRUM.
TAPE, 16k/48k: LOAD "" / LOAD ""CODE
You can use any home stereo tape deck with RCA output, and if you get any R Tape Loading Errors, or can't even get the basic loader to find the title, adjust the volume. The normal loading command is LOAD "". LOAD command is implemented in the letter J, so when you push the J key in "K" cursor mode (which is the default), the LOAD command will come on the screen instantly. Quotation signs can be typed in "L" cursor mode by pressing symbol shift and P. Some games require additional CODE command after the quotation signs, which can be found from the "E" cursor mode, which can be found be pressing the caps shift and symbol shift keys simultaneously. The CODE command is under the I key. Mostly, the games that require this loading command are originally released for the 16k Spectrum in the early days.
TAPE, 128k: menu
The later Spectrum models had a starter menu with an easy access 128k tape loader for all those gamers who couldn't bother to learn to write the loading commands. You would only have to choose the "tape loader" from the menu and press play on the cassette deck. Sometimes, though, the old 48k games wouldn't work with the 128k mode on, so you would have an option to choose the 48k mode, but then you'd have to type in the commands. After Amstrad had bought the worldwide rights to sell and manufacture all existing and future Sinclair computers and computer products, their first job was to make the +2 variant of the 128k Spectrum, which included a built-in tape drive, which meant that you couldn't connect any external cassette decks into the computer. Also, there was no volume adjuster, so if any load errors occured, you would have to adjust the tape head alignment screw
with a screwdriver down the little hole just below the tape slot.
DISK, 128k +3: menu
To make things even more modern, the +3 Spectrum only had a disk drive, but since the disks were of the same unusual 3" type which many Amstrad machines used, they were harder to come by in the real world populated by 3.5" and 5.25" floppies. Anyway, the best and least difficult way to load disks is to use the Loader option in the starter menu. If you experience problems with this, consult the +3 manual.
2. COMMODORE VIC-20/64/128/16/+4.
Most of the Commodore computers seems to have bundled with a tape drive, but there's a good reason for that: the tape input port is unique for all the Commodore machines, and the disk drive was almost as expensive as the computer so that not too many middle-class users could afford to buy a disk drive with the computer.
TAPE: LOAD (and RUN)
Starting with cassette loading, we've got the LOAD command, which, by default, will load the first item on the tape - you don't even need quotation marks here. Sometimes, if you only type LOAD and then load the first part of the loader from the tape, the program will stop loading after the basic sequence, and you have to type RUN to make it proceed with the machine code bits. To skip this bit, and make the loading much easier, just tap on SHIFT (or C=) and RUN/STOP to have the computer automatically add the RUN command after the first bit is done.
Mostly, if you're trying to load from an original disk, which will very likely have only one game, load the game by typing LOAD"*",8,1 which will load the first file from the disk. Sometimes, you need to load games by their filenames, so that would make it LOAD"FILE",8,1. You can view the directory of the disk by LOAD"$",8 and after having done so, LIST. If the C64 does nothing after loading a file, try launching it with RUN. Consult your disk drive manual if any errors are suspected.
On a C128, you only have to type DLOAD"FILE" or F2+"FILE" or RUN"FILE", and you can access the directory by simply pushing F3 or typing DIRECTORY. Most likely, you will still have to go to the C64 mode to get to play anything, so that is what GO64 command is for.
3. AMSTRAD CPC 464/4128.
The Amstrad machines come with either a tape drive or a disk drive in-built, but both interfaces can be bought separately. Whichever the case, if your only drive isn't the in-built cassette drive, you will need to type in |TAPE before you can load anything from cassette. Running a game from tape is easy enough, although it differs from the two previous computers rather a lot. Simply type RUN", or even more simply, press CTRL + ENTER, and do as you're told.
If you have both interfaces, a disk drive and tape, the disk drive will be the dominant one, and will automatically be in use. As for the commands, |DIR or CAT will show you what's on the disk; RUN"FILE for loading and running any binary, basic program or other executable; or just RUN" for the first file on the disk. Sometimes, if you get a read error with |DIR or CAT, restart the computer and type |CPM. The program may not work even then, but this is the final option.
4. ATARI 400/800 XL/XE.
This is getting a bit difficult. If you're in Atari Basic prompt, you can only load Basic programs with one of the following four commands, depending on how they were saved on the tape in the first place: CLOAD (saved with CSAVE), LOAD "C:" (saved with SAVE "C:"), ENTER "C:" (saved with LIST "C:") and RUN "C:" (similar to LOAD "C:" but also runs the program). Having loaded the program with any other command than RUN "C:" will need the RUN command to launch it.
If you're loading a machine code program, turn on the computer while pressing the START key, unless your Atari has a built-in Basic, in which case, you need to press START and OPTION simultaneously while turning on the computer. When the Atari gives you the beep signal, press play on tape and let go of the START (and OPTION) button(s). Finally, you need to press the RETURN key so the program will load.
Insert disk into drive before turning on the computer, and the program should automatically load once the computer is turned on. If you have an XL model Atari, press down the OPTION button while turning on the computer.
I've never seen a tape deck for MSX in use, but apparently there are several of them around, all customized for loading MSX programs. CLOAD["FILE"] will load the first Basic program on tape that the loader will recognize, or the one specified. BLOAD is a bit trickier, as it will load binary code, and needs to be specified from which device you are loading the file, and if it has a name, and if you want to execute it automatically. Thus, the complete syntax would be BLOAD"CAS:FILE",R
DISK: LOAD"*",R or RUN"*"
Depending on whether you're using MSX-DOS or MSX-BASIC, you'll have a bunch of different commands at hand for advanced use, but for the most time, LOAD"FILE",R or RUN"FILE" should be enough, and should be able to load both basic and binary files, if I've understood correctly.
6. BBC MICRO.
The Acorn computers are by far the most mysterious to me, and probably a whole lot of other retro gamers not born and raised in the United Kingdom. Both tape and disk interfaces are specific for the computer, so good luck on finding a good full set if you're interested.
According to Stairway to Hell website, the vast majority of tapes contain a Basic loader file, so they have to be loaded with this string of commands:
...which wouldn't be much of a problem, if the keyboard setup was even nearly similar to what the regular qwerty is like. However, if the first file on a tape is machine code, you'll start the loading with this string instead:
Most disks apparently contain a !BOOT file, which means that if you press SHIFT+BREAK, the program on the disk should load automatically. If you're emulating, it's most likely SHIFT+F12.
That's all for now, but if I ever have to use some even more obscure computers, I'll add them to this list if necessary.