Hello,
Do you think 1 GB RAM is sufficient for LXDE or XFCE leap installation ? 
Thanks !
I do not truly know. However I have run XFCE successfully on a 2 Gb very old (circa 2000 CE) machine. On a 1 Gb old machine I have run a base Debian installation.
Quoting from the Startup Guide:
1 GB physical RAM (at least 1.5 GB when using online repos, 4 GB or more strongly recommended)
so you should be able to install from the DVD, but I doubt that you will be able to do any serious work on that system, while it should be enough for a printer server or the like.
I too have a test install on a 2GB RAM system and I think that it is the minimum practical amount of RAM for graphical desktop use.
You might have better chances with the i586 32-bit version of Tumbleweed while it is available.
It might be. It depends on what you expect from it, and whether you can be satisfied doing few things or only one thing at a time. If you have a 32 bit PC, you can’t install Leap. If you have a 64 bit PC, it almost certainly supports more than 1GB of RAM, so should be increased to at least 2GB if not more for the best possible productivity and satisfaction whatever your DE selection.
The following is a real life view of 1GB RAM with no apps open except Konsole, shortly after booting, on a PC with Intel graphics, which shares system RAM (somewhere around 16kb):
# free
total used free shared buff/cache available
Mem: 998512 115720 423172 89340 459620 635968
Swap: 1052220 0 1052220
# inxi -SMCz
System: Kernel: 5.12.13-1-default i686 bits: 32 Desktop: KDE 3.5.10 Distro: openSUSE Tumbleweed 20210724
Machine: Type: Desktop System: Dell product: OptiPlex GX270 v: N/A serial: <filter>
Mobo: Dell model: 0DG284 serial: <filter> BIOS: Dell v: A07 date: 06/26/2006
CPU: Info: Single Core model: Intel Pentium 4 bits: 32 type: MCP cache: L2: 512 KiB
Speed: 2394 MHz min/max: N/A Core speed (MHz): 1: 2394
#
Here’s basically the same thing running Plasma, except with separate GPU with its own RAM, and 64 bits:
# free
total used free shared buff/cache available
Mem: 987012 418444 89988 13172 478580 407512
Swap: 1534172 0 1534172
# inxi -SMCz
System: Kernel: 5.12.13-1-default x86_64 bits: 64 Desktop: KDE Plasma 5.22.4 Distro: openSUSE Tumbleweed 20210729
Machine: Type: Desktop System: HP-Pavilion product: KJ385AA-ABA a6433w v: N/A serial: <filter>
Mobo: PEGATRON model: Benicia v: 1.01 serial: <filter> BIOS: American Megatrends v: 5.43 date: 09/10/2009
CPU: Info: Dual Core model: Intel Core2 Duo E7500 bits: 64 type: MCP cache: L2: 3 MiB
Speed: 1600 MHz min/max: 1600/2933 MHz Core speeds (MHz): 1: 1600 2: 1600
#
Both the above PCs are running both Samba and NFS servers in the background, among other tasks a default installation typically runs that can be disabled to free some RAM.
If you’re thinking XFCE is the lightweight its reputation suggests, or Plasma the heavyweight its reputation suggests, you ought to check these out:
https://www.linuxfordevices.com/tutorials/linux/kde-vs-xfce
https://www.forbes.com/sites/jasonevangelho/2019/10/23/bold-prediction-kde-will-steal-the-lightweight-linux-desktop-crown-in-2020/?sh=763cb23826d2
I have LXQt running on a 2007 notebook with 2GB RAM without any problems. As LXQt is slightly more demanding than LXDE (but less that XFCE) I suspect that, for most purposes, 1GB RAM plus 2GB swap would work fine as Linux is very good at managing memory needs. The main problem would be modern browsers like Chromium and Firefox which would struggle with 1GB RAM. But if it has a 64-bit chip and you can increase the memory to 2GB, you should have no problems with LXDE.
I don’t know XFCE and can’t tell if it will run. If yes, it seems you will have to rely on swap quite heavily. You may wish to have swap (or all /) on an ssd in that case.