class-single-multiple

IRAM Memo 2009-6
Read-write optimization in CLASS
S. Bardeau, J. Pety, S. Guilloteau
1. IRAM (Grenoble)
2. Observatoire de Paris
3. LAB, Observatoire de Bordeaux
March, 13 2009
Version 1.0

### Abstract:

CLASS is a GILDAS1 software for reduction and analysis of (sub)–millimeter spectroscopic data. It is daily used to reduce spectra acquired with the IRAM 30m telescope. CLASS is currently used in many other facilities (e.g. CSO, HHT, Effelsberg) and it is considered for use by Herschel/HIFI. CLASS history started in 1983. As a consequence, it was written in FORTRAN 77 and tailored to reduce pointed observations.

When CLASS was re-written in Fortran 90, it was decided to split On-The-Fly spectra into one observation each2. This eases spectra handling from the user side, but, of course, multiplies the number of observations in a single file (typically by a factor ). The increasing number of observations (especially with the OTF acquisition schemes) and number of channels of the back-ends produces larger and larger files. CLASS has thus been revised with new file types and optimized with a faster algorithm in order to ensure a maximal data rate from the software side. We will expose here this new algorithm, and show that the major limitation for writing CLASS large files is currently on the hardware side.

Keywords: On-The-Fly, CLASS file format, data rate, user and system times.

Related documents: IRAM memo 2005-1: Improved OTF support

- Contents
- Improved data format and algorithm
  - Historical status
  - Current version
  - Cross-use of the different types
    - New types
    - Backward compatibility
    - Transition
- Benchmark
  - Method
  - File size
  - Times
    - USER time
    - SYSTEM time
    - USER time vs SYSTEM time
  - Data rate
- Acknowledgments
- About this document ...