In ESXi 4.1, memory management operates at the hypervisor level without requiring explicit allocation to the host itself. The hypervisor uses a sophisticated memory management system that includes:

Physical RAM: 48GB (hardware)
Service Console: ~300MB (dedicated)
VMkernel: Dynamic allocation
VMs: 4GB each (configurable)

ESXi employs several advanced techniques to enable safe memory overcommitment:

• Transparent Page Sharing (TPS) - eliminates duplicate memory pages
• Balloon Driver - reclaims idle VM memory via vmware-tools
• Memory Compression - compresses least-used pages
• Host Swap - last resort using .vswp files

For your 48GB host running 13x4GB VMs (52GB total):

# esxcli system memory get
Maximum: 49152 MB
Reserved: 3072 MB
Free: 12288 MB

# Check active memory usage
esxtop -b | grep -i "mem"

Critical metrics to monitor in your scenario:

MEMCTL: Balloon driver activity
PSHARE: Page sharing efficiency
SWAP: Host swap usage
ZIP: Memory compression ratio

1. Enable memory reservation for critical VMs: vim-cmd vmsvc/get.config [vmid] | grep memReservation
2. Monitor active memory (not just allocated): esxcli system vm process list
3. Adjust VM memory limits based on actual usage: vim-cmd vmsvc/reconfigure [vmid] mem=[newsize]

Essential commands for memory analysis:

# Check current memory stats
esxcfg-info -m

# Verify balloon driver operation
vmware-toolbox-cmd stat balloon

# View memory compression stats
vsish -e get /memory/comptel

In VMware ESXi 4.1, memory management operates fundamentally differently from traditional operating systems. The hypervisor itself consumes approximately 300-500MB RAM for its core operations, automatically reserved during boot without explicit configuration.

// Sample ESXi memory statistics via CLI
~ # esxcli hardware memory get
Physical Memory:    49152 MB
Non-NUMA Memory:    49152 MB
Reserved:            512 MB
Available:         48640 MB

When you assign 4GB to each VM (13×4GB=52GB on 48GB hardware), you're using ESXi's memory overcommitment capability. Key techniques enable this:

• Transparent Page Sharing (TPS): Eliminates duplicate memory pages across VMs
• Balloon Driver (vmmemctl): vmware-tools component reclaims unused guest memory
• Memory Compression: Compresses less-active pages (introduced in later versions)
• Swap to SSD: Uses VMFS swap files when physical RAM is exhausted

Use these CLI commands to verify real consumption:

~ # esxtop -b -n 1 | grep -E "MEM|%MEM"
MEM|  4103MB| 11.1%|  22.9%| 100%| 0.00| 0.00| 0.00| 0.00
~ # vim-cmd vmsvc/getallvms | awk '{print $1}' | xargs -I {} vim-cmd vmsvc/get.config {} | grep -i mem
memorySize = "4096"
...

For your 48GB host running 13×4GB VMs:

1. Enable memory reservations for critical VMs: vmware-cmd /vmfs/volumes/datastore1/VM/VM.vmx setres.mem 2048
2. Configure shares appropriately: vim-cmd vmsvc/get.config | grep -A 3 memoryAllocation
3. Monitor swap usage: esxcli storage vmfs swap list

Sample memory metrics interpretation:

MEMORY
--------
PSHARE/MB: 1204    (savings from page sharing)
SWAP/MB:   512     (indicates memory pressure)
ZIP/MB:    256     (compressed memory)
VMKMEM/MB: 38      (hypervisor overhead)

When swap usage exceeds 10% of allocated memory, consider redistributing VM workloads or adding physical RAM.