what can't rhel do?

Specification	Version 3	Version 4	Version 5	Version 6	Version 7
Maximum logical CPUs 2
x86	16	32	32	32	N/A6
Itanium 2	8	256 [512]	256 [1024]	N/A6	N/A6
x86_64	8	64 [64]	160 [255]	240 [4096]	160 [5120]
POWER	8	64 [128]	128	128	128
System z	64 (z900)	64 (z10 EC)	101 (zEC12)	101 (zEC12)	101 (zEC12)
Maximum memory5
x86	64GB3	64GB3	16GB4	16GB4	N/A6
Itanium 2	128GB	2TB	2TB	N/A6	N/A6
x86_64	128GB	256GB [1TB]	1TB	6TB [64TB]	3TB [64TB]
POWER	64GB	128GB [1TB]	512GB [1TB]	2TB	2TB
System z	256GB (z900)	1.5TB (z10 EC)	3TB (z196)	3TB (z196)	3TB (z196)
Maximum number of device paths ("sd" devices)
	256	256 13	1,024 13,14	8,192 13,14	10,000 13,14
Required minimums
x86	256MB	256MB	512MB minimum/1 GB/logical CPU recommended	512MB minimum/1 GB/logical CPU recommended	N/A6
x86_64	256MB	256MB	512MB minimum/1 GB/logical CPU recommended	1GB minimum/1 GB/logical CPU recommended	1GB minimum/1 GB/logical CPU recommended
Itanium 2	512MB	512MB	512MB/1 GB/logical CPU recommended	N/A6	N/A6
POWER	512MB	512MB	1GB minimum/2GB recommended	2GB minimum/2GB required per install	2GB minimum/2GB required per install
Minimum diskspace	800MB	800MB	1GB minimum/5GB recommended	1GB minimum/5GB recommended	10GB minimum/20GB recommended
File systems and storage limits
Maximum filesize (Ext3)	2TB	2TB	2TB	2TB	2TB
Maximum file system size (Ext3)	2TB	8TB	16TB	16TB	16TB
Maximum file size (Ext4)	--	--	16TB	16TB	16TB
Maximum file system size (Ext4)	--	--	16TB [1EB]	16TB [1EB]	50TB [1EB]
Maximum file size (GFS)	2TB	16TB [8EB]	16TB [8EB]7	N/A	N/A
Maximum file system size (GFS)	2TB	16TB [8EB]	16TB [8EB]7	N/A	N/A
Maximum file size (GFS2)	--	--	100TB [8EB]	100TB [8EB]	100TB [8EB]
Maximum file system size (GFS2)	--	--	100TB [8EB]	100TB [8EB]	100TB [8EB]
Maximum file size (XFS)	--	--	100TB [8EB]	100TB [8EB]	500TB [8EB]
Maximum file system size (XFS)	--	--	100TB [16EB]	100TB [16EB]	500TB [16EB]
Maximum Boot LUN size (BIOS)	--	--	2TB	2TB10	2TB10
Maximum Boot LUN size (UEFI)	--	--	N/A	32bit (i686) - 2TB,  64bit - 16TB (tested limit)	50TB
Maximum x86 per-process virtual address space	Approx. 4GB	Approx. 4GB	Approx. 3GB4	Approx. 3GB4	N/A6
Maximum x86_64 per-process virtual address space		512GB	2TB	128TB	128TB
Kernel and OS features
Kernel foundation	Linux 2.4.21	Linux 2.6.9	Linux 2.6.18	2.6.32 - 2.6.34	3.10
Compiler/toolchain	GCC 3.2	GCC 3.4	GCC 4.1	GCC 4.4	GCC 4.8.2
Languages supported	10	15	19	22	22
NIAP/CC certified11	Yes (3+)	Yes (4+)	Yes (4+)	Yes (4+)	Under Evaluation (4+)
Common Criteria certified KVM11	--	--	Evaluated	Evaluated	Under Evaluation
IPv6	--	--	Ready Logo Phase 2	Ready Logo Phase 2	Under Evaluation
FIPS certified11	--	--	Yes (7 modules)	Yes (8 modules)	Under Evaluation (9 modules)
Common Operating Environment (COE) compliant	Yes	Yes	N/A	N/A	N/A
LSB-compliant	Yes - 1.3	Yes - 3	Yes - 3.1	Yes - 4.0	Under Evaluation (4.1)
GB18030	No	Yes	Yes	Yes	Yes
Client environment
Desktop GUI	Gnome 2.2	Gnome 2.8	Gnome 2.16	Gnome 2.28	Gnome 3.8
Graphics	XFree86	X.org	X.org 7.1.1	X.org 7.4	X.org 7.7
OpenOffice	V1.1	V1.1.2	V2.0.4 12	V3.2 12	LibreOffice V4.1.4 12
Gnome Evolution	V1.4	V2.0	V2.8.0	V2.28	V3.8.5
Default browser	Mozilla	Firefox	Firefox 1.5 12	Firefox 3.6 12	Firefox 24.5 12