Line printer art: (was Re: tape baking)

Dave Wade dave.g4ugm at gmail.com
Fri Jul 7 10:25:42 CDT 2017


> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Chuck
> Guzis via cctalk
> Sent: 07 July 2017 08:11
> To: CCtalk <cctalk at classiccmp.org>
> Subject: Re: Line printer art: (was Re: tape baking)
> 
> On 07/06/2017 10:42 PM, Dave Wade wrote:
> 
> > Sadly I don't think that’s much use on Hercules as it needs an AWS or HET
> file. Is there a format converter any where?
> 
> Dunno, but it should be pretty simple.  TAP is discussed with the SIMH
> documentation and the AWS format is discussed here:
> 
> http://www.cbttape.org/awstape.htm
> 
> Mostly a matter of reworking headers.   The surprising thing is that I
> know that some IBM tapes can have 128KB records--I don't know how AWS
> accommodates this with only 2 bytes for a record length.
> 
> And "long block" tapes can theoretically have a single block that's the length
> of the physical tape, although one would be an idiot to do such a thing.  (cf.
> CDC CYBER NOS/BE 1LT driver)


The header is six bytes long. Two are the length of the current block. Two of the bytes are the length of the previous block, so you can do read backwards, two of the bytes contain flag bits. 
One of the flags says this chunk  is the first part of a real block, another the last part, so typically both are set for blocks less than 64K. For blocks, bigger than 64K they the  first chunk flag is set for the first 64K, the last chunk has the last chunk bit set, and any intermediate chunks have no bits set. Again this facilitates read backwards....

> 
> --Chuck

Dave



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