Missing column and data in dataset

I had a request with 493 samples with 24 variables. After receiving approval, I downloaded the file named ipumsi_00001 with .dat extension. There is only one file in it and there are only 3 columns in the file. Is there anything I should pay attention to about the file? Where am I making a mistake? Which way do you recommend to open the .dat file?

By default, our data are compressed (*.dat.gz). You will need to decompress or unzip them before using them. I recommend 7zip as a free decompression software for Windows and The Unarchiver for Macs. Additionally, the standard format for data requests is a fixed-width text file; we provide an accompanying syntax file to read the data into a statistical analysis package, such as Stata or SPSS. This blog post provides guidance on how to change your data request to a different format (e.g., a CSV file or a file that can be opened directly in Stata).

We also caution users against requesting extracts with a large number of samples and to instead focus on the particular samples that are required for the research statement provided in the data application. A compressed file with 100 samples can typically be a gigabyte in size and the unzipped version will be many times larger. With each sample potentially having tens of millions of observations (see sample details), a typical system running a statistical package such as Stata or R will not be able to process this much data. With .csv files the cap is even lower since Excel will display a maximum of 1,048,576 total rows.