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From: John Cowan <>
To: Dan Cross <>
Cc: Paul Ruizendaal <>, "" <>
Subject: [TUHS] Re: x/y/zmodem on Unix
Date: Mon, 18 Sep 2023 23:58:42 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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On Mon, Sep 18, 2023 at 7:08 PM Dan Cross <> 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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  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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