[Info-vax] Backup TK50 tapes

[David Froble]

Johnny Billquist wrote:
> On 2013-02-25 21:27, glen herrmannsfeldt wrote:
>> Paul Sture <nospam at sture.ch> wrote:
>>> In article <kgfcuq$9f1$1 at Iltempo.Update.UU.SE>,
>>> Johnny Billquist <bqt at softjar.se> wrote:
>>
>>>> Actually, I think for most hardware, the limit is actually 64k
>>>> for one read.
>>
>> I have read/written 100K on unix 9track drives.
> 
> What system?
> 
>>> I believe that is correct.  However I purposely restricted VMS backup
>>> tapes to a maximum of 32K because that meant I could copy savesets to
>>> disk.
>>
>> Is that a VMS limit or DEC hardware limit?
> 
> If the 32K really is a limit, I believe it would be in VMS, in treating 
> a 16-bit number as signed here.
> The controllers that I know by DEC have 16 bit fields for record lengths 
> in hardware, but it is unsigned.
> 
>     Johnny
> 

I'm going to take a guess here and state that the 32K limit was in VMS. 
  Specifically, there is a VMS limit of 32K for string lengths.  The 
string descriptors use 16 bits to specify the string size.  I'm going to 
guess that string descriptors might have been used to specify buffers. 
16 bit length, 32 bit address ...