[Info-vax] Example of random access by record number on an RMS fixed record size, relative organization file?

[gah4]

On Wednesday, September 20, 2023 at 7:37:33 PM UTC-7, Hein RMS van den Heuvel wrote:

(snip)

> For Relative files RMS divides the file up into buckets (default = big enough to hold 1 at least record. 
> It first calculates records/bucket (RPB) integer divide of bucketsize*512 and (one (flag byte) plus Maximum Record Size). 
> Next calculate VBN as 1 (File Prologue) plus integer divide of record number by RPB times RPB. 
> Read BKS * 512 bytes, and locate the record. 

For comparison OS/360, not all that long before VMS, writes disk tracks with
physical blocks equal to the record lengths.  (Sequential files are normally written
with blocked records, but again they are written to the physical block length.)

Disks are accessed by cylinder, track, and block within the track.  OS knows how
many blocks are on a track, and calculates the track and record within the track.
That made more sense in 1963 than it did later.

More recent OS work the same way, but the disk drives emulate the count-key-data
system using fixed-block disk drives.