Re: ancient OS history, ARM is sort of channeling the IBM 360

On 6/25/2024 8:41 AM, Scott Lurndal wrote:

"Stephen Fuld" <SFuld@alumni.cmu.edu.invalid> writes:

Scott Lurndal wrote:
>

 

And even on the mainframes, the records were blocked and read
in larger chunks and the application deblocked them.

>
Sure.  But lets use a typical example of reading 80 column card images
blocked 10, so an 800 byte disk record (remember, this is IBM, CKD type
disks, so really 800 byte records on the disk).  So for ten out of
every eleven reads, the read verb just meant a single load of the base
address of the next record in the block.

 Same thing on Unix.  Read 800 bytes at a time and treat it as 10
80-byte records.

But if you are using the "standard" Unix file system, doesn't it read the block(S) into its cache, then when the user program does the read, transfer the data from its cache into the user's variables?  That is the extra overhead to which I was referring.

Modern unix/linux systems will anticipate sequential accesses
and do anticipatory loads such that data is already in memory
when the next "record" is needed.

Sure.  But isn't it in the file system cache, so you still have to transfer the data to the user program's variables?
--
  - Stephen Fuld
(e-mail address disguised to prevent spam)