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Comment by pavlov | Hacker News Reader

I believe CP/M always used the forward slash as the CLI modifier argument prefix (where Unix would use a dash). MS-DOS inherited this.

When directories were eventually added, the forward slash couldn’t be used as a separator because it was already used for modifiers.

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MS-DOS did have a function to change the option character (INT 21h, AH=37h) [1], and the "kernel" always accepted both '\' and '/' as a path separator (and that is still the case today; the shell however, is another story). The same call can also change MS-DOS to require "/DEV/" before device names. [2]

[1] Documented for MS-DOS 2.0; documentation removed for MS-DOS 3.0; still available (according to my source) through at least MS-DOS 3.30

[2] God, why do I still remember this information thirty years later? Sigh.

CP/M does not use forward slash as the CLI modifier.

Examples - from the standard CP/M utilities (CP/M 2.2)

ASM FILE.ABC

.ABC encodes options. Source file for ASM is always .ASM

STAT uses $ - STAT FILE $R/O sets file to read-only PIP A:=B:[G0] - PIP (copy, "peripheral interchange program"), uses [ for options, as do later Digital Research programs (like the linker). Basically /no/ Digital Research use of / as option separator.

Microsoft used / - for example the command line L80 FILE,FILE/N/E - which means link FILE.REL (relocatable), naming the output FILE.COM, and link and exit.

CP/M 2.2 introduced "user areas" - a disk could be divided into 16 user areas (USER 0 to USER 15). There was no "searching" until CP/M 3. CP/NET (Digital Research networking) used [ as a separator. Examples (from CP/NET documentation)

A>RMAC SNIOS A>LINK SNIOS[OS]

would log in to server 01, with password secret

NETWORK B:=D:[F]

assigned B: to server 0F, drive D:

The lack of directories was not such a loss, as the maximum disk size for CP/M 2.2 was 8MB. Remote drives with CP/NET could be much larger (I have used up to 1TB).

Forward slash as a modifier prefix was IBM's desire because it was what they used in Mainframe OSes at the time. A lot of MS-DOS things were for "compatibility" with IBM Mainframes at the time. Supposedly, Microsoft was lightly against the forward slash as command argument because they preferred Unix machines at that point as development mainframes and liked the POSIX defaults for forward slash as directory separator. (Which is why MS-DOS even from the early days of the file system often supported both for directory slash in first party commands, even if individual app argument parsers from third parties did not.)

> Forward slash as a modifier prefix was IBM's desire because it was what they used in Mainframe OSes at the time. A lot of MS-DOS things were for "compatibility" with IBM Mainframes at the time

Not true. On IBM mainframes, options are generally specified in a NAME=VALUE or NAME(VALUE) format. For example, here is a TSO command to allocate a dataset: ALLOCATE DATASET(ALLOC.FILE1) NEW DIR(4) TRACKS SPACE(2,3) DSORG(PO) RECFM(F) LRECL(80) BLKSIZE(800) CATALOG

VM/CMS uses an open parenthesis to introduce options instead, for example: LISTFILE (LABEL

The forward slash option style does not come from IBM mainframes.

Nor (despite what many people think) does it come from CP/M – CP/M's own option style was to put options in square brackets: PIP B:=A:*.COM [G9 V]

Not sure exactly where CP/M gets that from, but may be very vaguely inspired by IBM mainframe conventions (especially VM/CMS), with square brackets replacing parentheses for whatever reason, and using single characters to save memory and typing.

What I actually believe happened: forward slash comes from DEC via Microsoft. Microsoft's development tools for CP/M used that option style, which Microsoft got from DEC, because they didn't like CP/M's native option style. QDOS/PC-DOS/MS-DOS 1.0 copied that Microsoft option style.

Yes, IBM did tell Microsoft not to change it from / to - between PC-DOS 1.0 and PC-DOS 2.0. But that was simply because IBM cared more about backward compatibility between DOS 1.0 and DOS 2.0 than Microsoft themselves did. It was nothing to do with mainframes.

The only thing about DOS which shows any strong direct IBM influence, in terms of actual syntax/terminology/concepts/etc, is code pages.

This is not true.

Most mainframe OSes have flat filesystems which do not have the concept of subdirectories.

They also do not use command switches.

The behaviour was almost certainly inherited from DEC TOPS-10:

http://www.os2museum.com/wp/why-does-windows-really-use-back...

This is not a mainframe OS, or an IBM one either. It ran on a 36-bit DEC minicomputer, the PDP-10.

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