I have a question to those who own/once owned/have played the disk versions of Infocom games … Would you get multiple disks which you’d have to replace as you played along? Like, “please insert disk 2”? Because I know the late z6 graphical Infocom games did, but I’m not sure if the original games were small enough that that wasn’t a problem. If so, then how would memory be stored across disks?
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I never had to do it on c64 (as I remember), but I think Atari had a smaller disk capacity so you sometimes needed two sides/disks. @8bit_era may know (alot) more…
EDIT: Found this - Z-machine standards / Atari 8-bit targets
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No, you never needed two disks, I played almost all of the Infocom games, even their later ones, and I never had to switch disks on a TRS-80 or C-64.
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I can confirm what @heasm66 said. I bought all the Atari 8-bit games. The first few games (Zork I, II, III and Starcross) came on a single-sided disk, so there was no disk swapping. From Deadline onwards, they came on a double-sided disk. It would load the interpreter and the memory-resident part of the story file, then prompt you to insert side 2. Once that had been inserted, there was no more disk swapping, except when you saved or restored a game. I can’t remember if you had to flip the disk when you restarted the game.
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Confirm what Henrik posted: Only 8-bit Atari versions was on two disks/sides (dunno if there was already “flippy disks” around when the atari 8b versions was released…)
Best regards from Italy,
dott. Piergiorgio.
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I had the Amiga version of Arthur (lost the box over the years), but I believe it was on one diskette.
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Some of the later C64 releases came on a double sided 5.25" disk, so you’d have to take the disk out and put it in up side down when prompted. Here’s my C64 Sherlock disk, note “Other side is SIDE 2” written on the label. I don’t recall ever seeing multiple disks in an Infocom release.
I believe that all the C64 Z-code version 5 releases were like this, with the interpreter on side 1 and the game data on side 2. The Z-code version 3 releases all fitted on one side of the disk.
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What David said.
A disk side on the C64 can fit about 170 KB of data. A z3 game needs about 10 KB for loader and interpreter, and up to 128 KB for the game.
You’d never need to change or flip disks while playing the game - the way a Z-code story file is organized, the interpreter has to have access to the entire story file at all times, while the game is running. A story file consists of dynamic memory and static memory. z4 and z5 games can be split up so the loader, interpreter and dynamic memory is stored on side 1, while static memory is stored on side 2 (or side 1 and side 2 can instead be two separate single-sided disks). Dynamic memory contents are then loaded into RAM at game start, and remain in RAM for the entire game. Once you flip the disk, the interpreter can read any part of static memory at any time.
The z4 and z5 games released for C64 were Nord & Bert (z4), Sherlock (z5) and Border Zone (z5). All of them were too big to fit on one disk side. Sherlock was even too big (185 KB) to fit the entire story file on one disk side, but the static memory part fit and that’s enough.
z4 and z5 games can be up to 256 KB in size. It’s no coincidence that some of them were small enough that the static memory would fit on a C64 disk side - Infocom planned exactly which platforms they would release a game for, and the author(s) had to keep the game file within the size constraints for that platform.
From 1987 and on, Infocom could also have released larger games for the C64, using the 1581 disk drive (holding 800 KB in one disk), but so few people owned 1581 drives that such releases would have been pointless from a commercial perspective.
Today you can build C64 disk images for a Z-code game using this scheme at https://ozmoo.online (Select build mode S2)
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Apple 2 disks were a little smaller (140k), but the arrangement was similar to the C64. I don’t remember which disks were double-sided though.
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The Amstrad CPC/PCW were all single-sided iirc, but there weren’t any releases of the later larger games.
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@zarf Definitely BorderZone, Sherlock and Hitchhiker (Solid Gold). I tested these interpreters last year for the Puny BuildTools. I can confirm it’s a similar logic as the Atari 8-bit, though not the same. I was able to get my own games running in Infocom’s late Atari 8-bit 2-disk interpreter but never managed to get anything running in the Apple II 2-disk terps. I also suspect some of the Z4 games on the Apple II to prompt for a disk swap, e.g. Trinity, though I haven’t tested this.
@Warrigal The statement that Infocom’s late Atari 8-bit interpreter has the resident memory on one side of the disk is not entirely true but somehow made its way into the Z-Machine Standards document. Instead Atari 8-bit story files for the late interpreter set the resident memory marker to 8FFF, regardless of its initial value, and the story file is always split at the 8FFF offset, which is roughly 36k. I wrote an article about it some time ago when I managed to get things running in Infocom’s late terp. Z-machine standards / Atari 8-bit targets
@heasm66 I talk about the Atari 8-bit disk sizes in the article I linked above 
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I’ve played some Apple II Infocom games that came on flippy disks (flip over). I don’t remember which games.
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Looking at the largest version of each game from the Obsessively Complete Infocom Catalog, we see (measured in kilobytes):
84 starcross
88 zork3
92 infidel, zork2
104 witness, suspended
112 cutthroats, enchanter, sorcerer, deadline
116 seastalker, suspect, hollywoodhijinx
128 lurkinghorror, stationfall, ballyhoo, plunderedhearts, spellbreaker, zork1, moonmist
136 planetfall
156 hitchhiker
160 leathergoddesses
164 wishbringer
168 nordandbert
176 borderzone
196 sherlock
240 bureaucracy
256 beyondzork, trinity, amfv
268 arthur
276 journey
296 zork0
340 shogun
These are just the Z-files; the corresponding disk images would have been bigger (especially: sound and graphics assets aren’t represented above).
The oldest IBM PCs had single-sided drives with 160K per side, but before long the drives were double-headed and seamlessly gave you 320K per disk without need for flipping.
Even the largest text-only games (Trinity and AMFV) were single-disk for the PC, and even at least some of the smallest graphic games. But the Apple II’s 5 ¼" drive was 140K per side, so the larger text games would have had to have been double-sided (and that meant flipping).
Judging by the pics, some of the graphic games had as many as 4 5 ¼" floppies in them.
The Internet Archive has a bunch of actual Infocom disk images, but looking at pictures on Ebay was more useful.
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This is true for z3 games, but for z5 Infocom took advantage of the fact that the Apple II’s disk drive is software-controlled to format the second disk as a 157kb 18-track disk instead of a normal 140kb 16-track disk.
I assume the idea was to reduce memory requirements by putting more of the game on the second disk, but this also functions as a rudimentary form of copy protection (as many players have inadvertently discovered to this day).
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Thanks, Prevtenet !
I’ll look in that section of the Internet Archive the reports of that guy with a pre-dawn nick 
on late apple ][ infocom disks…
… and surprise ! the largest apple disk he dealt was HHGG r56 in october '17, whose was noted as single-sided with custom OS:
Name: The Hitchhiker's Guide to the
Galaxy
Version: release 56 / 841221
Genre: adventure
Year: 1984
Publisher: Infocom
Platform: Apple ][+ or later
Media: single-sided 5.25-inch floppy
OS: custom
[...]
READING FROM S6,D1
T00,S00 FOUND DOS 3.3 BOOTLOADER
USING DISK'S OWN RWTS
WRITING TO S5,D2
T00,S02,$FC: BC -> AD
T00,S02,$5D: BC -> AD
COMPLETE.
resulting in a normal 143360 bytes image.
(the relevant .z3 is 113444 bytes long, at least the one in Zarf’s catalog)
Best regards from Italy,
dott. Piergiorgio.
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