How do I make sure that a custom ROM will fit my HTC Desire? After rooting your phone and setting S-OFF you will probably want to flash a custom ROM. One thing to consider when flashing a new ROM is the size of the partitions. This is especially important for phones like HTC Desire which has limited internal memory. I will use HTC Desire as an example here but the same principle should apply to other HTC models as well.
The HTC Desire by default allocates 250 MB of its internal memory for the /system partition, 40 MB for /cache partition and 147 MB for /data partition.

The ROMs are usually packed in ZIP files and are usually about 155 MB in size. However, they do get bigger when unpacked. Here's how to verify that you will be able to flash a custom ROM on your phone.


Download the ROM you want to flash. I will use SuperNova ROM here as
example.
Unpack the ZIP file. In my case, this is
Supernova_2.4.0.1_signed.zip.
Right click on the system folder and click Properties. Note the
size of it. In my case this is 203 MB.
Right click on the data folder and click Properties. Note the size
of it. In my case this is 17.9 MB.
Compare the found sizes to the reference sizes above.


If your system folder is less than 250 MB and your data folder is less than 147 MB then it's all good. You will be able to flash the ROM using the stock HBOOT image. This is true in my case for example.

However, if you find that your data folder is bigger than 147 MB (which is unlikely), OR if you want more free space for things like apps and user data, then you will need to flash a different HBOOT image first which will layout the partitions differently so that you get more memory allocated to the /data partition. One such HBOOT image is called "Bravo Oxygen r2". For more information and to download a differen HBOOT image, go to the AlphaRev website.

What is contained in the system and data folders is what will get copied to the corresponding partition once you flash the ROM.