# DOS drive-alias component

`RIALIAS.COM` is a session-scoped DOS pathname compatibility component. It has
no executable, filename or game-name rules and no built-in drive topology.
Mappings are injected as command-line profile data, for example:

```text
RIALIAS.COM /A=C /B=D
```

Each mapped pathname is copied to a 260-byte resident scratch buffer before the
configured source drive is replaced. The caller-owned pathname buffer is never
edited by the component. Mapping is single-hop: `/A=B /B=C` maps an explicit
`A:` path to `B:`, not transitively to `C:`.

Supported classic `INT 21h` pathname APIs:

- `AH=39h`, `3Ah`, `3Bh`: create/remove/change directory (`DS:DX`)
- `AH=3Ch`, `3Dh`, `41h`, `43h`: create/open/delete/attributes (`DS:DX`)
- `AH=4Bh`, `4Eh`: execute and find-first (`DS:DX`)
- `AH=56h`: rename, including source `DS:DX` and target `ES:DI`
- `AH=5Bh`: create-new (`DS:DX`)
- `AH=60h`, `6Ch`: truename and extended-open input (`DS:SI`)

Explicitly outside this component's scope:

- FCB APIs and FCB drive bytes
- `AH=0Eh` drive selection followed by unqualified relative paths
- APIs whose drive is passed as a numeric field rather than a pathname
- `AH=5Ah` create-temporary-file because its pathname buffer is an output
- paths longer than the 259-byte payload plus terminator
- BIOS `INT 13h`, controller ports and other direct disk I/O

Unsupported calls are chained unchanged. The component only affects explicit
`X:` pathname prefixes covered by injected mappings.