From: John Cowan <cowan@ccil.org>
To: Dan Cross <crossd@gmail.com>
Cc: Paul Ruizendaal <pnr@planet.nl>, "tuhs@tuhs.org" <tuhs@tuhs.org>
Subject: [TUHS] Re: x/y/zmodem on Unix
Date: Mon, 18 Sep 2023 23:58:42 -0400 [thread overview]
Message-ID: <CAD2gp_R5LedwgqQqXd+2J_MjMBeenLL_VRudzMc206ojJ5s7Vw@mail.gmail.com> (raw)
In-Reply-To: <CAEoi9W69XgxkQbWBK3OQ3-JemxRdkeUMau6YOtfFJALemdLBSw@mail.gmail.com>
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On Mon, Sep 18, 2023 at 7:08 PM Dan Cross <crossd@gmail.com> wrote:
but there was no total byte
> count, so it was assumed that the final block would be padded with a
> throwaway character.
>
CP/M, like RT-11 and OS/8 before it, did not track the sizes of files in
bytes or words, only in blocks. Text files ended in ^Z and were then
padded with either NULs or more ^Zs if necessary; binary files were usually
padded with NULs.
ZMODEM was, as I understood it, designed for transfers across telenet,
> which was pretty reliable; instead of the highly synchronous
> send/wait-for-ack cycle of xmodem and ymodem, zmodem relies on error
> detection and correction and is basically a streaming protocol: a
> packet in a sliding window could be NAK'ed, thus rewinding the
> transfer, but otherwise it basically just sends data until done.
>
It's an analogue of TCP/IP, in fact.
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next prev parent reply other threads:[~2023-09-19 3:59 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-18 22:31 [TUHS] " Paul Ruizendaal
2023-09-18 23:07 ` [TUHS] " Dan Cross
2023-09-19 2:04 ` Theodore Ts'o
2023-09-19 9:47 ` Michael Stiller via TUHS
2023-09-19 3:58 ` John Cowan [this message]
2023-09-19 2:46 ` Jonathan Gray
2023-09-19 3:42 ` Serge Burjak
2023-09-19 6:10 ` Serge Burjak
2023-09-19 6:37 ` Dave Horsfall
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