The VAX is running

Daniel Seagraves dseagrav at
Sat Apr 4 13:36:39 CDT 2009

A block is a sequence of tape frames. Those can be 7 or 8 bits wide 
depending on your hardware. Blocks have length, and can vary in length 
from block to block. You can have a small descriptor block between long 
data blocks on the tape, where the small block describes what the next 
large block contains, and so on. You can tell if a block is a 
descriptor by its length, or looking for a magic number at the start of 
the block, or whatever.

Tapes also have file-marks.

On Apr 4, 2009, at 1:29 PM, Richard wrote:

> In article <2877e57dba24bc750739ccec428ded28 at>,
>     Daniel Seagraves <dseagrav at>  writes:
>>> In article
>>> <f4eb766f0904031640g7c90507eo92411f16365021e1 at>,
>>>     Ethan Dicks <ethan.dicks at>  writes:
>>>> Back in the day, we used to move copies around on magtape, bypassing
>>>> all sorts of stream-of-bytes issues.  Today, of course, most things
>>>> expect streams of bytes, so that's how most things are presented.
>> On Apr 4, 2009, at 12:53 PM, Richard wrote:
>>> How does magtape avoid the stream-of-bytes issue?
>> Magtape has blocks.
> What exactly is a block?
> Is it defined as a sequence of bits or as a sequence of bytes?
> If its just a sequence of bytes that define a block, I'm not sure I
> understand how blocks avoid the stream-of-bytes issue.
> -- 
> "The Direct3D Graphics Pipeline" -- DirectX 9 draft available for 
> download
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